NOT my vehicle. My friend told me his 2006 Sienna LE has now gone 819 miles and used 28.636 miles = 28.6 MPG. Some city, more highway. On a round trip highway test drive at 55 - 60 MPH the Sienna had a phenomenal 36.0 MPG (using calculator).
DaimlerChrysler stupid, cheap policy of removing nice features is one reason I have been looking more seriously at the Odyssey and Sienna.
From postings here and RW experience of friends, the 5 speed Quest seems to get better mileage than the Honda and possibly the Sienna. Only folks I know with the Sienna drive around town mostly, or have the AWD version. Our 05 Quest has exceeded all expectations and with 19,000 miles Nissan seems to have remedied the quality problems that hampered the 04's.
I put the gear in neutral a lot due to the hilly terrain in our area. I found that this helps with the fuel economy a lot. Does anyone know if it's harmful to the transmission? Thanks.
UNWISE. :mad: Better just to turn cruise off if you want to save fuel. However, is saving fuel worth increasing the risk of having an accident because your speed increases so much you create an unsafe situation? Most newer Automatic Transmissions automatically downshift to keep your speed at the set speed.
I don't use cruise due to the hilly terrain here. I know some think leaving the car in neutral is unsafe, which seems to make some sense. But one can always excersize more caution when doing so. I'm not concerned with the safety aspect, but rather the health of the transmission when the gear is shifted frequently between D and N.
Dominick, What is the amount of miles you have registered on your odometer between fills? I can do no more than like 400, and with a 18 gal fillup I see it more like 24mpg.What dealer in what state do you deal with most. :confuse:
Hi folks... old timer here. Have enjoyed having a T&C since Aug.'94. If memory serves it has the 3.7L V6. It now has 186k miles... water pump went out at 102k, transmission at 103k, exhaust system still the original! Have had the engine gone over with a fine tooth comb every 75k... new belt, plugs, etc. Oh... the coolant tubes to the back A/C unit have been replaced twice... seems they are prone to corrosion, assumed road salt through pin-hole breaks in the cladding from road grit damage.
Oh.. guess the subject was mpgs... When it was new, we got 21-22 mpg on road trips, and about 15-17 around town (depending on whether the wife, or I was driving it). Now that it's showing it's age, highway mileage seldom is better than 18-19, and around town we routinely average 14-15.5.
It's going to see mostly short to/from work use now that we have a "new-to-us" 300C for those longer traveling trips.
Coasting in neutral actually decreases MPG in most cases.
The reasoning goes something like this: Assume you are travelling at a speed of 25 mph or higher. If you take your foot off the gas pedal while your transmission is in gear, the computer is programmed to completely shut down the fuel flow to the cylinders since no gas is needed to keep the engine turning. But, if you put your transmission in neutral and coast, the engine needs gas to continue turning so the electronic brain instructs the fuel delivery system to send gas to the cylinders.
But that only applies to autos with electronic fuel injection systems.
(If your auto has a carburetor, air pressure continually forces some quantity of fuel mixture into the intake manifold of a spinning motor regardless of gas pedal position or transmission gear selection.)
So, in nearly all modern autos since 1978 or so, coasting in neutral is not a good idea. It can be hazardous to your health and decrease your car's fuel mileage.
Dominick, If your driving 400 miles then you are looking at 22 to 25MPG, because the Ody has a 17 or 18 Gal tank. Now if you only had a 14 gallon tank and went 400 miles than yes 28 mpg is right. I'm in Florida and the temp is finally dipping in the 70's, so the economy may do better, but I'm only getting 23 - 25 with a good tail wind; with the same car. I was hoping my dealer could comunicate with your dealer and exchange computer settings and make my 05 ody do 30MPG :sick: .
Thanks for the thoughts. I find that a little hard to believe. An engine constantly needs gas to stay running. When our van is in gear and coasting downhill with foot off gas pedal, the engine tends to stay around 2K RPM (designed engine braking). This tells me considerable amount of gas is being supplied to the engine. When doing the same in neutral though, RPM drops to 700 RPM, which means MUCH less gas being burned. Also from the trip computer, I know for sure that our van gets MUCH better mileage in neutral when coasting (as high as +60 mpg, for that moment of course).
I find that by coasting for just 2-3 miles downhill in neutral at about 45-50 mph, I can increase the mileage by close to 2 mpg.
The engine rpm at 2000 when coasting tells you nothing about the amount of gas being supplied to it. Why? Because when coasting in gear, the tires are forcing the axles to turn. Not the other way around. And, take it a bit further... the tires are powering the gears of the trans-axle or differential and transmission, and (if an automatic) the torque converter too. And the torque converter is driving the engine, even if no gas is being sent to it at all. But in neutral, the engine has to have gas to keep turning because not the tires, nor anything else, is making it turn. But even before you brought up the idea of engine braking, I decided to alter my previous statement that coasting will usually decrease gas mileage (if you are thinking of the gas mileage for an entire trip and not just the coasting portion of the trip). The point being, that while in gear, drag from motor friction and other internal mechanical and fluid couplings between the crankshaft and the tires create some resistance to the vehicle's continued motion. If you later have to use gas to regain whatever momentum was lost due to that engine braking and drivetrain drag, then you might actually use more gas for your entire trip than if you had coasted in neutral and then put it back in gear again when you needed to feed the motor gas to accelerate or maintain some desired speed. Yes, gravity will give you more free acceleration when your car is in neutral than when it is in gear because there is not drivetrain braking in neutral. But if you don't need that free force to maintain your desired speed, then you are wasting gas by putting your auto in neutral as you coast. So, to restate my original position more accurately, during that distance that you are coasting, downhill or otherwise, you will get better gas mileage in gear with your foot off the gas pedal than if you coasted that same distance in neutral. (again, only if you have electronic fuel injection) Does anyone out there get it yet?
...from your trip computer, you know for sure ...?
Maybe not. You need to check with an expert on this, but I'm pretty sure the instantaneous gas mileage function of your trip computer works by measuring engine vacuum, and not by measuring fuel flow. It is in effect a vacuum gauge comparing vacuum to miles per hour (mph), not a fuel meter. As such, it does not accurately reflect miles per gallon (mpg) while coasting in neutral.
i'm with you from the standpoint that the vehicle when in gear and foot off the accelerator, or in neutral is still burning fuel...
i would not be placing my vehicle in neutral during coast down a hill. you would not be in a position to apply the throttle if necessary. the 2MPG instantaneous increase wouldn't be worth it to me.
also re-engaging D from N while at considerable speed....are you sure you aren't stressing the transmission components more by doing so?
These new cars are smarter than we are. With fuel injectors, unlike a carburetor, fuel flow is actually turned on and off by the computer. (In a carburetor, air flow is regulated which indirectly controls gasoline flow.) When the electric switch in the fuel injection system stops fuel flow to an injector, no gas enters the combustion chamber even if the intake valve is open. But in an air pressure operated carburetor some amount of fuel will be pushed into the combustion chamber anytime the intake valve is opened.
Did anyone in here take courses in automotive technology?
i understand the basic concept of fuel injection and the use of solenoids modulated with a certain duty cycle (time on vs. time off per given unit of time) to regulate flow.
what i contend is if you are coasting, you are still consuming fuel.
fuel flow is one thing keeping the injector from over-heating and failing.
I get 21.5 mpg this is with 67K, Yes I drive tons and I love this car. This is a 85-15 mix of highway and city driving everyday (85=highway, 15=city). I normally travel 100 miles each day with 15 of those miles inside the city limits. All those calculations of higher mpg than this I suspect. While it may seem that the mpg is nice come back to me in two years.
"But, if you don't need that free force to maintain your desired speed..."
As when one is going down a steep hill? Perhaps shifting into and out of neutral going downhill to regulate speed would be more fuel efficient. Not that I would ever do that. My name may be the Jipster...but come on people...thats something the late great cheapster Jack Benny wouldn't have done. Well, actually HE probably would have. :sick:
What I meant was if you are in neutral and coasting down anything more than a very slight hill, your car will accelerate to an undesirable excessive speed due to gravity unless you ride the brakes. In that case, you don't need that acceleration from gravity. Instead, if you keep it in gear and coast, you not only save the gas that would have been used to keep your engine at idle speed, you also save your brakes and may be able to maintain a perfectly stable desired speed by allowing drivetrain drag to partially overcome that gravity. Shifting in and out of gear will wear out various transmission parts prematurely unless you are very good at matching engine speed to transmission speed at the moment before you put it back into gear. That goes for automatic or manual transmissions. It is a good idea to use an appropriate transmission gear which will provide the correct amount of drag so you can coast and keep the car at the desired speed on a long mountain downgrade without having to use your brakes a lot (so long as you do not over-rev your motor in doing so). It may prevent your brakes from overheating and fading and prevent the fluid from boiling due to overuse. Both are dangerous conditions.
In order to maximize fuel economy and minimize emissions, modern cars are programmed to eliminate fuel flow to the cylinders when coasting unless that fuel is needed to keep the engine turning near idle speed. Spark and combustion is also curtailed which means no additional heat is being produced. Fuel flow through the injectors is not necessary to keep them cool while coasting. Do an internet search and try to find a qualified person's opinion; I already did. Most of what you read on here is just some yahoo's guess.
I have been following this conservation about coasting vs in gear decelerating, and fail to see how you can come up with your theory. All systems wether carburetor or FI, have either an idle stop, or a throttle position sensor. It makes more sense to me if your foot is off the acellerator, and your car is idling (in neutral) downhill, and your RPM is at 750, then you are using less fuel than if your trans is in drive, and the RPM downhill is 2000! The FI system will still provide fuel to keep the engine running at 2000. The speedometer and RPM guage are linked together in Accellerating and decelerating in gear, but not so when decelerating in Neutral. Granted putting your trans into Neutral frequently is not good, and as someone said dangerous, but it will conserve fuel over leaving it in gear. (not sure it is worth the trouble) I'm not sure about the possibility of the rear wheels working in reverse to decelerate your car either. I remember some years ago that you couldn't push some model cars to start them (automatics), because they didn't have a rear trans fluid pump, and therefore you couldn't turn the engine over by the wheels. With all the inovations today with the automatic transmission, maybe that is not true now. I know my '04 EX has a 5 speed overdrive trans, and it seems to pick up speed downhill when in cruise control. Not sure if it is the overdrive (free-wheeling) or what. My old '88 Gran Caravan holds the speed even --up, down, or flat ground. Just MHO
This is not religion or voo-doo. No faith is needed. It is mechanics and physics - black and white. Read a book if you need to.
I have a few questions too:
"The speedometer and RPM gauge are linked together"...?
Now where did you get that idea? Why would you think they are in any way linked? The speedometer displays the speed of the car relative to the road underneath the wheels by measuring the rotational speed of either the driveshaft or a part in the transmission. It is simple math. But don't change the diameter of your tires; it will cause your speedometer to be inaccurate. The engine tachometer (or RPM gauge) displays the rotational speed of the crankshaft in the motor, that's all. No magical speedometer connection needed. In fact, if you removed the entire motor from the car at 60 mph, your speedometer would still read 60 mph. Or, if you removed your speedometer from the dash while coasting at 2200 RPM your tach would still read 2200 RPM.
"...downhill is 2000! The FI system will still provide fuel to keep the engine running at 2000"...?
That is precisely opposite from the truth. If what you say is true, then the engine RPM would never be reduced while coasting (presumably regardless of road grade?) because, "The FI system will still provide fuel to keep the engine running at 2000." (Your words, not mine.) Hahaha. You crack me up! That is nearly the same as cruise control, except instead of the car's speed being held constant, your system would keep engine RPM constant. Actually, the engine needs no fuel to rev at 2000 when coasting in gear. You can prove this to yourself if you are foolish enough to turn your ignition key off at 60 mph. No fuel will be flowing and no combustion taking place, but your engine will still be humming along at that same 2000 rpm. (But depending on the grade of the road and wind conditions your car and engine RPM may decelerate, accelerate or maintain speed.) BUT DON'T DO IT ! You'll have no power steering or brakes and your steering wheel my lock too. (Although it is true that somewhere between 700 and 1500 rpm or so the engine management system will start injecting fuel again.)
"... I'm not sure about the possibility of the rear (do you mean drive?) wheels working in reverse to decelerate your car either"....?
Now it also sounds like you are doubting the existence of engine braking in an automatic transmission cars too. Is that what you are saying? Anyone can test this by coasting in gear and comparing your rate of deceleration to that which occurs if you coast in neutral.
"It makes more sense to me"...?
Don't try to make sense out of this stuff ! Re-read my posts and do an internet search. Read what qualified people have to say. Don't try to re-engineer the modern auto in your head. It will just make your head ache and it probably embarrasses the car.
(You need many more answers than these. Maybe someone else can pitch in to set you straight on all the rest.)
Maybe Dominick refills his tank before it is bone dry. Then his figure could be 28 and still accurate. (most of us do not run out of gas and then fill up)
You say, "...I know my '04 EX has a 5 speed overdrive trans, and it seems to pick up speed downhill when in cruise control. Not sure if it is the overdrive (free-wheeling) or what. My old '88 Gran Caravan holds the speed even --up, down, or flat ground."
Your EX is coasting downhill if it is accelerating away from the speed where you set the cruise control. If the downhill was only slight then cruise speed would remain constant. Your Grand Caravan, with cruise control on, would also speed up downhill if the downgrade was steep enough. It would also be coasting during that time. If both cruise controls were set to the same speed and the road and weather conditions were the same for both cars, then the difference in the resulting downhill speeds is due to the difference in the rolling resistance (including engine braking, drivetrain friction and aerodynamic drag) of each car.
I guess I have to modify my response to the question of MPG coasting in neutral vs coasting in gear. Maybe I should have said with a manual transmission. Then you have a definite disconnect from the drive-line, -no engine braking. I know that there is definitely engine braking with automatic trans, but the initial question is whether you get more mpg going downhill in neutral or leaving the car in gear. About the Tach and speedometer. I know that there is no physical connection between the tach and the speedo, but it is the relationship to each other that I was refering to, and the resulting effect of coasting in gear vs neutral. I have to admit that I'm no expert in the most modern computer-controlled engine management systems, but it still seems to me that if you are rolling downhill, with the engine in gear, and the trans braking the engine, and the RPM decreasing from 2000 or whatever number to the idle RPM you are using more fuel than coasting in neutral with the RPM already at 750 or whatever idle RPM. I know that the older Carb engines would. Maybe you are right about the computer controlled engines of today shutting off the FI when decelerating, but they sure don't show it in the resulting MPG that I experience. One last thing - Once in a taxi ride from Leesburg, VA to Wash. D.C. (25 mi) The driver kept putting the trans in neutral and coasting whenever possible, and I asked why? The answer- saving fuel. He must have noticed a difference in consumption, otherwise, why do it.
We're talking here about modern fuel-injected cars. (I pointed out some differences they have with carbureted ones earlier.)
"...coasting in neutral vs coasting in gear. Maybe I should have said with a manual transmission..."
It makes no difference whatsoever. If you put either transmission in neutral while coasting, the motor is disconnected from the driveshaft. If you leave either in gear while coasting, there will be a connection between them transmitting torque in one direction or the other.
"...no physical connection between the tach and the speedo..."
It makes no difference whether they are connected or not connected. It makes no difference what they are reading relative to each other. So long as the motor is above 1500 or so while coasting in gear (foot off the accelerator pedal), no gas is being sent to the cylinders.
"... but it still seems to me ..."
It makes no difference how it "seems" to you. Nor how it seems to me. What matters is how autos are designed and manufactured. Opinions don't change those facts.
"...in the resulting MPG that I experience..."
How do you calculate your MPG? And what do you do to make certain all other variables other than coasting in gear/neutral are equal in your testing?
"... Once in a taxi ride..."
And in ten other taxis that day, the gas mileage conscious drivers were keeping their cars in gear as they coasted. So what? People do things and say things. But it does not change the physical state of the cars they are in.
Research the question and find answers from credible experts. You don't have to go through the rest of your life guessing about this.
The only problem I have with following all this is the ascertion that the FI system 'detects' when the wheels are driving the engine through the transmission rather than the other way around and automatically shuts off all fuel when this state is detected.
I'm a bit lazy this a.m. - could you point me to a not-to-technical link which would explain how the FI system detects this state?
.. is to monitor the intake manifold pressure. When the drivers lets go of the gas pedal since the vehicle is, say going down a grade, then the intake manifold pressure drops (high vacuum), which signals the ECU that no fuel should be sent to the injectors. When the drivers presses the gas pedal, say when wanting to accelerate, the intake manifold pressure rises (drop in vacuum) which tells the ECU to send an approrpriate amount of fuel.
Please note there are several other more complex ways to do this in an even more precise way.
The computer monitors and makes adjustments for load on the engine, throttle position, speed, weather conditions, fuel quality, engine condition and temperature, etc. You might try the Society of Automotive Engineers or your neighborhood genius. Hahaha. Lazy and honest is more noble than hard working and dishonest, right? I salute you. Use your search engine. See where you end up. Its fun.
"You might try the Society of Automotive Engineers or your neighborhood genius. "
Didn't have the intestinal fortitude to wade through the SAE stuff. A bit short of neighborhood genius's at the moment (in both the real-world neighborhood as well as the TownHall neighborhood). Although apparently the supply of Townhall 'wiseacres' is ample. (use of my prefered terminology usually results in a deleted post, but I think you get my drift).
However, in a discussion of the various components of Bosch FI systems, I ran across this:
OVERRUN CUTOFF VALVE A) This component curtails fuel delivery during coasting/deceleration conditions. The overrun cutoff valve will direct excess air into the intake manifold to stop fuel delivery when conditions of closed throttle, warm engine, and engine speed over a preset rpm are met (either coasting or decelerating). AKA) Decel Valve, Coasting Cutoff Valve.
So, this would support your point that modern EFI systems (at least Bosch and I have no reason to believe other systems are different) do cut the fuel delivery while coasting in gear.
Relax Joe. We're trying to have some fun here and at the same time getting a few technical things figured out. No need to exhibit that kind of attitude.
In the real world, it's probably hard to see the difference in gear or neutral when coasting downhill. 1). Let's say no fuel is supplied when in gear. Still the question is how much fuel is supplied when in neutral? 2). When in gear you get engine braking which limits coasting speed (when no cop around ), which would require fuel later on to regain. It's probably a wash in the end.
Why do you say this: "...cut and curtail imply reduction, not inhibit or stoppage..."
Cambridge Dictionary of American English Definition curtail to reduce or limit (something), or to stop (something) before it is finished He had to curtail his speech when time ran out.
by it's use in the sentence, because i haven't located one explaination of FI which states that there is complete stoppage of fuel flow when the vehicle is in gear and going down hill with your foot off the accelerator, and because i believe there needs to be continuous flow (even if very small) to cool the injectors and also keep the cylinders at temperature.
These words themselves don't necessarily mean a COMPLETE stoppage. They simply mean to signaficantly reduce. E.g. "The OPEC decided to cut their production...". It doesn't mean they decided to STOP production. Or we're all screwed
Maybe we should just turn this whole question over to 'Mythbusters' and see if they can resolve it.
I would experiment by towing a running vehicle at 60mph with a flow meter installed on the fuel line. Read the flow meter with the vehicle in gear and being towed (to simulate the vehicle on a downgrade and coasting), and compare that to the meter reading with the towed vehicle in neutral.
I'd also like to see an actual link posted by averigejoe backing up his claim. It's easy to make a claim and then propose OTHERS do the research to verify it.......because I admit that the language in the info I posted is not conclusive one way or the other.
Why do you think curtail, "...by it's use in the sentence...", does not mean stop? And anyway, the very next sentence makes it very clear that curtail does mean stop.
You say, "...haven't located one explaination of FI which states that there is complete stoppage of fuel flow when the vehicle is in gear and going down hill with your foot off the accelerator..."
But here is the link and the explanation: http://www.forparts.com/fi.htm The overrun cutoff valve will direct excess air into the intake manifold to stop fuel delivery when conditions of closed throttle, warm engine, and engine speed over a preset rpm are met (either coasting or decelerating). AKA) Decel Valve, Coasting Cutoff Valve. (Can you see how that exactly fits the situation and restates many of the past points in my posts? And stop means stop,right? Haha, reminds me of Bill Clinton.)
Remember, your belief or faith (or mine) will not redesign these cars.
And you say, "... keep the cylinders at temperature..."
"...cutoff valve will direct excess air into the intake manifold to stop fuel delivery..."
I'm curious - how does directing excess air into the intake manifold 'stop' fuel delivery? Wouldn't it be simpler (if the complete stoppage of fuel were desired) to simply install a solenoid valve in the fuel rails?
I agree with you averigejoe, the FI systems are capable of determining closed throttle with RPMs in a given range (decel) and stop fuel to the cylinders.
"...If the engine revolution exceeds a certain limit (between 1,200 and 1,500 usually) and the throttle is closed— this is called deceleration—, the momentum of the car is sufficient to rotate the engine through the wheels. To save fuel, the injectioniscut off. As soon as the engine speed drops below the limit or the throttle is opened, the injection is reintroduced..."
Yeah, now that sounds really familiar, doesn't it.
But that all depends, of course, on what the meaning of "is" is. Hahahahahahah. What a clown! (Bill Clinton and his ilk)
Yes, I think it's pretty credible. IMO, the presentation is very good, and covers a lot of ground, hitting on the various sensors and their contribution to the overall operation of the system. It's the best thing I've come across. If you've got something better, why not post it? However, this thread is better taken to How It Works. I'm sure the Host is going to pop in and steer people back onto Van Mileage. Regards.
Comments
From postings here and RW experience of friends, the 5 speed Quest seems to get better mileage than the Honda and possibly the Sienna. Only folks I know with the Sienna drive around town mostly, or have the AWD version. Our 05 Quest has exceeded all expectations and with 19,000 miles Nissan seems to have remedied the quality problems that hampered the 04's.
ps: Our Quest has an automatic transmission.
Better just to turn cruise off if you want to save fuel. However, is saving fuel worth increasing the risk of having an accident because your speed increases so much you create an unsafe situation?
Most newer Automatic Transmissions automatically downshift to keep your speed at the set speed.
What is the amount of miles you have registered on your odometer between fills? I can do no more than like 400, and with a 18 gal fillup I see it more like 24mpg.What dealer in what state do you deal with most. :confuse:
Oh.. guess the subject was mpgs... When it was new, we got 21-22 mpg on road trips, and about 15-17 around town (depending on whether the wife, or I was driving it). Now that it's showing it's age, highway mileage seldom is better than 18-19, and around town we routinely average 14-15.5.
It's going to see mostly short to/from work use now that we have a "new-to-us" 300C for those longer traveling trips.
The reasoning goes something like this: Assume you are travelling at a speed of 25 mph or higher. If you take your foot off the gas pedal while your transmission is in gear, the computer is programmed to completely shut down the fuel flow to the cylinders since no gas is needed to keep the engine turning. But, if you put your transmission in neutral and coast, the engine needs gas to continue turning so the electronic brain instructs the fuel delivery system to send gas to the cylinders.
But that only applies to autos with electronic fuel injection systems.
(If your auto has a carburetor, air pressure continually forces some quantity of fuel mixture into the intake manifold of a spinning motor regardless of gas pedal position or transmission gear selection.)
So, in nearly all modern autos since 1978 or so, coasting in neutral is not a good idea. It can be hazardous to your health and decrease your car's fuel mileage.
If your driving 400 miles then you are looking at 22 to 25MPG, because the Ody has a 17 or 18 Gal tank. Now if you only had a 14 gallon tank and went 400 miles than yes 28 mpg is right.
I'm in Florida and the temp is finally dipping in the 70's, so the economy may do better, but I'm only getting 23 - 25 with a good tail wind; with the same car.
I was hoping my dealer could comunicate with your dealer and exchange computer settings and make my 05 ody do 30MPG :sick: .
I find that by coasting for just 2-3 miles downhill in neutral at about 45-50 mph, I can increase the mileage by close to 2 mpg.
But in neutral, the engine has to have gas to keep turning because not the tires, nor anything else, is making it turn.
But even before you brought up the idea of engine braking, I decided to alter my previous statement that coasting will usually decrease gas mileage (if you are thinking of the gas mileage for an entire trip and not just the coasting portion of the trip). The point being, that while in gear, drag from motor friction and other internal mechanical and fluid couplings between the crankshaft and the tires create some resistance to the vehicle's continued motion. If you later have to use gas to regain whatever momentum was lost due to that engine braking and drivetrain drag, then you might actually use more gas for your entire trip than if you had coasted in neutral and then put it back in gear again when you needed to feed the motor gas to accelerate or maintain some desired speed.
Yes, gravity will give you more free acceleration when your car is in neutral than when it is in gear because there is not drivetrain braking in neutral. But if you don't need that free force to maintain your desired speed, then you are wasting gas by putting your auto in neutral as you coast.
So, to restate my original position more accurately, during that distance that you are coasting, downhill or otherwise, you will get better gas mileage in gear with your foot off the gas pedal than if you coasted that same distance in neutral.
(again, only if you have electronic fuel injection)
Does anyone out there get it yet?
Maybe not.
You need to check with an expert on this, but I'm pretty sure the instantaneous gas mileage function of your trip computer works by measuring engine vacuum, and not by measuring fuel flow. It is in effect a vacuum gauge comparing vacuum to miles per hour (mph), not a fuel meter. As such, it does not accurately reflect miles per gallon (mpg) while coasting in neutral.
i would not be placing my vehicle in neutral during coast down a hill. you would not be in a position to apply the throttle if necessary. the 2MPG instantaneous increase wouldn't be worth it to me.
also re-engaging D from N while at considerable speed....are you sure you aren't stressing the transmission components more by doing so?
With fuel injectors, unlike a carburetor, fuel flow is actually turned on and off by the computer. (In a carburetor, air flow is regulated which indirectly controls gasoline flow.) When the electric switch in the fuel injection system stops fuel flow to an injector, no gas enters the combustion chamber even if the intake valve is open. But in an air pressure operated carburetor some amount of fuel will be pushed into the combustion chamber anytime the intake valve is opened.
Did anyone in here take courses in automotive technology?
what i contend is if you are coasting, you are still consuming fuel.
fuel flow is one thing keeping the injector from over-heating and failing.
I think from now on I'll stop this practise. I wasn't sure in the 1st place which is why I asked. It's not worth taking the risk.
As when one is going down a steep hill? Perhaps shifting into and out of neutral going downhill to regulate speed would be more fuel efficient. Not that I would ever do that. My name may be the Jipster...but come on people...thats something the late great cheapster Jack Benny wouldn't have done. Well, actually HE probably would have. :sick:
Shifting in and out of gear will wear out various transmission parts prematurely unless you are very good at matching engine speed to transmission speed at the moment before you put it back into gear. That goes for automatic or manual transmissions.
It is a good idea to use an appropriate transmission gear which will provide the correct amount of drag so you can coast and keep the car at the desired speed on a long mountain downgrade without having to use your brakes a lot (so long as you do not over-rev your motor in doing so). It may prevent your brakes from overheating and fading and prevent the fluid from boiling due to overuse. Both are dangerous conditions.
Fuel flow through the injectors is not necessary to keep them cool while coasting.
Do an internet search and try to find a qualified person's opinion; I already did. Most of what you read on here is just some yahoo's guess.
Granted putting your trans into Neutral frequently is not good, and as someone said dangerous, but it will conserve fuel over leaving it in gear. (not sure it is worth the trouble)
I'm not sure about the possibility of the rear wheels working in reverse to decelerate your car either. I remember some years ago that you couldn't push some model cars to start them (automatics), because they didn't have a rear trans fluid pump, and therefore you couldn't turn the engine over by the wheels. With all the inovations today with the automatic transmission, maybe that is not true now.
I know my '04 EX has a 5 speed overdrive trans, and it seems to pick up speed downhill when in cruise control. Not sure if it is the overdrive (free-wheeling) or what. My old '88 Gran Caravan holds the speed even --up, down, or flat ground.
Just MHO
Boxwrench
I have a few questions too:
"The speedometer and RPM gauge are linked together"...?
Now where did you get that idea? Why would you think they are in any way linked? The speedometer displays the speed of the car relative to the road underneath the wheels by measuring the rotational speed of either the driveshaft or a part in the transmission. It is simple math. But don't change the diameter of your tires; it will cause your speedometer to be inaccurate. The engine tachometer (or RPM gauge) displays the rotational speed of the crankshaft in the motor, that's all. No magical speedometer connection needed. In fact, if you removed the entire motor from the car at 60 mph, your speedometer would still read 60 mph. Or, if you removed your speedometer from the dash while coasting at 2200 RPM your tach would still read 2200 RPM.
"...downhill is 2000! The FI system will still provide fuel to keep the engine running at 2000"...?
That is precisely opposite from the truth. If what you say is true, then the engine RPM would never be reduced while coasting (presumably regardless of road grade?) because, "The FI system will still provide fuel to keep the engine running at 2000." (Your words, not mine.)
Hahaha. You crack me up!
That is nearly the same as cruise control, except instead of the car's speed being held constant, your system would keep engine RPM constant.
Actually, the engine needs no fuel to rev at 2000 when coasting in gear. You can prove this to yourself if you are foolish enough to turn your ignition key off at 60 mph. No fuel will be flowing and no combustion taking place, but your engine will still be humming along at that same 2000 rpm. (But depending on the grade of the road and wind conditions your car and engine RPM may decelerate, accelerate or maintain speed.) BUT DON'T DO IT ! You'll have no power steering or brakes and your steering wheel my lock too. (Although it is true that somewhere between 700 and 1500 rpm or so the engine management system will start injecting fuel again.)
"... I'm not sure about the possibility of the rear (do you mean drive?) wheels working in reverse to decelerate your car either"....?
Now it also sounds like you are doubting the existence of engine braking in an automatic transmission cars too. Is that what you are saying? Anyone can test this by coasting in gear and comparing your rate of deceleration to that which occurs if you coast in neutral.
"It makes more sense to me"...?
Don't try to make sense out of this stuff !
Re-read my posts and do an internet search. Read what qualified people have to say.
Don't try to re-engineer the modern auto in your head.
It will just make your head ache and it probably embarrasses the car.
(You need many more answers than these. Maybe someone else can pitch in to set you straight on all the rest.)
You say, "...I know my '04 EX has a 5 speed overdrive trans, and it seems to pick up speed downhill when in cruise control. Not sure if it is the overdrive (free-wheeling) or what. My old '88 Gran Caravan holds the speed even --up, down, or flat ground."
Your EX is coasting downhill if it is accelerating away from the speed where you set the cruise control. If the downhill was only slight then cruise speed would remain constant.
Your Grand Caravan, with cruise control on, would also speed up downhill if the downgrade was steep enough. It would also be coasting during that time.
If both cruise controls were set to the same speed and the road and weather conditions were the same for both cars, then the difference in the resulting downhill speeds is due to the difference in the rolling resistance (including engine braking, drivetrain friction and aerodynamic drag) of each car.
I guess I have to modify my response to the question of MPG coasting in neutral vs coasting in gear. Maybe I should have said with a manual transmission. Then you have a definite disconnect from the drive-line, -no engine braking. I know that there is definitely engine braking with automatic trans, but the initial question is whether you get more mpg going downhill in neutral or leaving the car in gear.
About the Tach and speedometer. I know that there is no physical connection between the tach and the speedo, but it is the relationship to each other that I was refering to, and the resulting effect of coasting in gear vs neutral.
I have to admit that I'm no expert in the most modern computer-controlled engine management systems, but it still seems to me that if you are rolling downhill, with the engine in gear, and the trans braking the engine, and the RPM decreasing from 2000 or whatever number to the idle RPM you are using more fuel than coasting in neutral with the RPM already at 750 or whatever idle RPM. I know that the older Carb engines would. Maybe you are right about the computer controlled engines of today shutting off the FI when decelerating, but they sure don't show it in the resulting MPG that I experience.
One last thing - Once in a taxi ride from Leesburg, VA to Wash. D.C. (25 mi) The driver kept putting the trans in neutral and coasting whenever possible, and I asked why? The answer- saving fuel. He must have noticed a difference in consumption, otherwise, why do it.
The ShadeTree Mechanic
Boxwrench
"...coasting in neutral vs coasting in gear. Maybe I should have said with a manual transmission..."
It makes no difference whatsoever. If you put either transmission in neutral while coasting, the motor is disconnected from the driveshaft. If you leave either in gear while coasting, there will be a connection between them transmitting torque in one direction or the other.
"...no physical connection between the tach and the speedo..."
It makes no difference whether they are connected or not connected. It makes no difference what they are reading relative to each other. So long as the motor is above 1500 or so while coasting in gear (foot off the accelerator pedal), no gas is being sent to the cylinders.
"... but it still seems to me ..."
It makes no difference how it "seems" to you. Nor how it seems to me. What matters is how autos are designed and manufactured. Opinions don't change those facts.
"...in the resulting MPG that I experience..."
How do you calculate your MPG? And what do you do to make certain all other variables other than coasting in gear/neutral are equal in your testing?
"... Once in a taxi ride..."
And in ten other taxis that day, the gas mileage conscious drivers were keeping their cars in gear as they coasted. So what? People do things and say things. But it does not change the physical state of the cars they are in.
Research the question and find answers from credible experts.
You don't have to go through the rest of your life guessing about this.
I'm a bit lazy this a.m. - could you point me to a not-to-technical link which would explain how the FI system detects this state?
Please note there are several other more complex ways to do this in an even more precise way.
You might try the Society of Automotive Engineers or your neighborhood genius.
Hahaha. Lazy and honest is more noble than hard working and dishonest, right? I salute you.
Use your search engine. See where you end up. Its fun.
Didn't have the intestinal fortitude to wade through the SAE stuff. A bit short of neighborhood genius's at the moment (in both the real-world neighborhood as well as the TownHall neighborhood). Although apparently the supply of Townhall 'wiseacres' is ample. (use of my prefered terminology usually results in a deleted post, but I think you get my drift).
However, in a discussion of the various components of Bosch FI systems, I ran across this:
OVERRUN CUTOFF VALVE
A) This component curtails fuel delivery during coasting/deceleration conditions.
http://www.forparts.com/fi.htm
So, this would support your point that modern EFI systems (at least Bosch and I have no reason to believe other systems are different) do cut the fuel delivery while coasting in gear.
Keep it in gear and coast.
Save $.
Protect lives and property.
Sleep well tonight!
averigejoe, can you point to a site which explains this. I've done a search and didn't come across anything as useful as what rorr came up with.
thanks.
I'm sorry.
Ask if you want.
I'll decide whether to answer too.
In the real world, it's probably hard to see the difference in gear or neutral when coasting downhill. 1). Let's say no fuel is supplied when in gear. Still the question is how much fuel is supplied when in neutral? 2). When in gear you get engine braking which limits coasting speed (when no cop around
I already mentioned that before.
Cambridge Dictionary of American English
Definition
curtail
to reduce or limit (something), or to stop (something) before it is finished
He had to curtail his speech when time ran out.
I would experiment by towing a running vehicle at 60mph with a flow meter installed on the fuel line. Read the flow meter with the vehicle in gear and being towed (to simulate the vehicle on a downgrade and coasting), and compare that to the meter reading with the towed vehicle in neutral.
I'd also like to see an actual link posted by averigejoe backing up his claim. It's easy to make a claim and then propose OTHERS do the research to verify it.......because I admit that the language in the info I posted is not conclusive one way or the other.
You say, "...haven't located one explaination of FI which states that there is complete stoppage of fuel flow when the vehicle is in gear and going down hill with your foot off the accelerator..."
But here is the link and the explanation:
http://www.forparts.com/fi.htm
The overrun cutoff valve will direct excess air into the intake manifold to stop fuel delivery when conditions of closed throttle, warm engine, and engine speed over a preset rpm are met (either coasting or decelerating). AKA) Decel Valve, Coasting Cutoff Valve.
(Can you see how that exactly fits the situation and restates many of the past points in my posts? And stop means stop,right? Haha, reminds me of Bill Clinton.)
Remember, your belief or faith (or mine) will not redesign these cars.
And you say, "... keep the cylinders at temperature..."
Hahaha. What do you mean by that?
I'm curious - how does directing excess air into the intake manifold 'stop' fuel delivery? Wouldn't it be simpler (if the complete stoppage of fuel were desired) to simply install a solenoid valve in the fuel rails?
http://xantiaclub.net/techguide/
I agree with you averigejoe, the FI systems are capable of determining closed throttle with RPMs in a given range (decel) and stop fuel to the cylinders.
regards.
http://xantiaclub.net/techguide/
"...If the engine revolution exceeds a certain limit (between 1,200 and 1,500 usually) and the throttle is closed— this is called deceleration—, the momentum of the car is sufficient to rotate the engine through the wheels. To save fuel, the injection is cut off. As soon as the engine speed drops below the limit or the throttle is opened, the injection is reintroduced..."
Yeah, now that sounds really familiar, doesn't it.
But that all depends, of course, on what the meaning of "is" is. Hahahahahahah. What a clown! (Bill Clinton and his ilk)