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Scion MPG-Real World Numbers



  • toriktorik Posts: 1
    Since buying my manual xB new in 05, I have consistently averaged 35 mpg. On two occasions of almost total highway driving, my xB got just over 40 mpg and I think on any long trip it would do it again. I must add, however, that I drive in a moderate manner, tending to stay 5 mph under any posted speed limit. Also, shifting smoothly and into the highest appropriate gear as soon as possible helps. My xB now has 24K miles and I am mostly happy with it. The most annoying thing about the car are the three raised child safety seat latch covers on the back of the rear fold down back rests. When loading anything into the car from the back, with the seat backs laid down, it will catch on them and have to be helped over them.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,482
    Sometimes I wish I could drive in a reasonable manner, but living as I do in California, if I drove 60 mph on the freeways I'd be killed. And once over 70 mph, the xA fuel mileage drops 10% at least.
  • 29.4 MPG over my first 2,100 miles, which has been a nice surprise, given much of it is stop-and-go commute.
  • I work in the Washington, DC area and live in West Virginia. I do a 112 mile round trip commute. I also would like to be able to drive in a reasonable manner. If I did I'd be flattened like a squirrel. If traffic allows 70-80 is the norm regardless of the posted limits on all interstates and secondary roads.

    I just changed my oil, filter, and air filter on the 05 XB before this last tankful, and set tire pressure at 35 psi all around. Penzoil Synthetic 5W30, Purolator Pure One oil filter, and Purolator air filter. I gassed up today and got 355.3 miles out of the tank. I filled 10.8 gals. for 32.89 mpg. I consider this a coup and the XB seems to be running better that ever at 72K miles.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,482
    That's pretty good. What annoys me about Scions is the small gas tank. I'd like to have a 15 gallon tank in there.
  • hbgti1hbgti1 Posts: 16
    I've had mine for less than a month. Over the first 700 miles my running average has been 33mpg. I've been taking it easy trying to keep revs below 3k RPM. I would say that I drive a good mix of hwy/city as the computer calculated an average speed of 24mph. When I finally decided to buy the xB, the gas mileage was my only concern, but now that I know that it's capable of getting the same mileage as the car it replaced ('99 Escort), I am more than pleased with it.
  • jim314jim314 Posts: 491
    The 195 60 15 tires are not only wider (by 5.4%) than 185 60 15, but they are also larger in diameter by 2.0%. The diameters are 24.21" and 23.74", respectively. Did you correct for this in doing your mpg calculations?

    To correct a distance travelled and the raw mpg values using the 195 tires, you multiply by 24.21/23.74 = 1.020. If you got 34.0 mpg on a tank, the corrected value would be 34.7 mpg.
  • How annoying is the 3500 rpm at 70 mph? I'm considering a 2005 with 80,000 miles, but that RPM was pretty alarming. Lot of reviewers commented about the high RPM and a couple said the AC was pretty weak.

    2700 rmp auto vs 3500 rpm manual makes it hard to believe they get comparable gas mileage.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,482
    3500 isn't bad at all if you keep the stock muffler It's a bit annoying with a sport muffler but again, certainly not obnoxious.

    80,000 miles is a lot of miles. I hope you're getting a really great price on it. That's a huge knock-off in value.

    Gas mileage will average out about 32-34.

    The AC takes a while to cool the car. On the highway, it will cool fine in 10-15 minutes. In heavy traffic on a very hot day, you'll have to keep the blower on high--which really makes a racket.
  • You know, I hadn't thought of that. I'm glad you brought that up and now I feel even better with the increased MPG. Sorry for the late post but I was in the process of ending my old job and starting a new one and have not logged in for a while. My driving commute is now cut in half as I can now take public trans and get reimbursed by the company.
  • They wanted $7300 which I thought was very reasonable. It was very clean and in very good shape.

    I ended up buying a new 08 Yaris sedan 5 speed with cruise & power package. I can't live without cruise control. The RPMs are still kind of high (3000) at 70 mph, but it didn't sound quite so buzzy as the 05 scion.
  • jim314jim314 Posts: 491
    The relatively high rpms at 70 mph for these small engines (3000 compared to say 2250 rpm for larger cars) just means that the engine is operating higher in its power band than the more overpowered engines in other cars. One way to look at this is that the Scion engine is properly sized for it application.

    Gasoline engines have their highest efficiency (lowest brake specific fuel consumption, BSFC) when operated at 50% to 80% of their maximum power output. A Scion cruising at 70 mph is still below this range because it is probably only developing 25 to 30 hp, but this is a higher fraction than more powerful vehicles.
  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,482
    I found the Scion's fuel economy quite good up to 70 mph, after which it tended to fall off 10% or so.

    Yeah, the Yaris sounds like a better deal for you all around.
  • otis12otis12 Posts: 171
    I dont get why the tC has a 4-speed auto when 2.4L is hooked up to a 5-speed auto in other Toyota models. Anyone know if Scion plans to upgrade from the 4-speed to 5-speed auto tranny????
  • I rolled 76,000 miles on my 2005 auto XB, and to celebrate I changed my oil and filter with Mobil 1 and a Purolator Pure-One filter. The oil was on sale for $19 and the filter for $5. I also put my snow tires on (185 60 15 Blizzacks-3rd season). Calculated MPG with this set up was 33.68 mpg for with 80% highway driving at speeds up to 80 mph. I'm extremely pleased with this car and my 16 yr. old daughter has taken aim at it for her 1st car. Maybe when I roll it to 100k I'll give it to her.
  • You have put some miles on yours! I have almost hit 20,000. The new Yokohamas I just put on in the 195 60 15 size has done wonders for the car. I wish Scion would on some REAL tires the first time.

    Still averaging 34 in my x box.

    I wish the Element got 34, but I did manage 25 in it, once.
  • Yes,
    I've driven the XB a lot. My commute is now half of what it was but I still do about 60 miles daily. The MPG has stayed right around 32-33 except when I use Flying J truck stop gas.

    Flying J gas is cheaper by up to 30 cents/gal. but only gives me 27-29 MPG, and has provided less mileage in every vehicle that I have owned. It must be watered down. All other gas brand name gas consistently gives me 32-33 in the box.

    Too bad about the MPG on the Honda. I like the Element immensely and am considering it as a future replacement for my XB but am not impressed by the mpg. The Element with the Honda diesel motor would be in my garage already if it were available.
  • Now that I've run all of the Flying J semi-gas out of the 05 XB the MPG improved significantly with the BP regular that I used to refill. I just filled up 10.3 gal and logged 359.7 miles for an MPG of 34.92. Driving mix was 80% highway and 20% city. Highway speeds from 55-80 mph. The low tank light had just turned on so I filled up and was happy with both the mpg and performance.
  • dwynnedwynne Posts: 4,018
    Didn't you say you are no longer the "crazed commuter" in that you took a job a lot closer to home? I am sure your xB will be relieved :D .

    I have been getting around 25 mpg on my 06 xB, but it has the auto slushbox and it is nearly all around town. I have also been making use of the remote starter on cold morning and leaving the office. When you pull out of our lot you are in a 45 mph zone that changes to 55 in less than 1/4 mile and the tranny will not upshift into 4th until the water temp his 140 or so, so if I know I am heading that way I will remote start it on my way out the door.

    I also have a lead foot :-)

    I also only have 7k or so on the clock since this is my "snow day" car - or was until I got rid of my RX-8. I would expect with more miles the mileage should pick up.

    My wife has a highway trip coming up in a couple of weeks and I may let her take the box. Partly because it has snow tires on it, partly to keep the miles off of her car, and also to see what kind of MPGs it will return. Her I4 Accord normally gets 23-24 around town and 29-31 on a trip.

  • Yes, although I have cut my commute in half to 60 miles/day, I now take a commuter bus an additional 27 miles farther than I used to. So I guess in reality I'm still a crazed commuter. I know, it's a suicidal day. I wake up at 3 30 am and get home at 6 30 pm. I drive 30 miles to a nice commuter bus and let them do the driving so I can sleep and/or read. I get reimbursed to ride and it saves me gas and traffic nightmares.

    I also live less than a mile from a major interstate and have the same issues with the tranny lock out while cold. During some of the extremely cold days I drove through some side streets just to warm up the tranny for the interstate drive.

    My wife took the box on a trip to Pittsburgh once and complained about the lack of cruise control. She never took it again on an extended drive although she likes the visibility and comfort of the car. 20 years ago we bought an S-10 Blazer and she's been a biased SUV driver since.
  • dwynnedwynne Posts: 4,018
    I had my oil and filter changed yesterday and made sure it was done to the full mark on the stick.

    My owner's manual calls for 3.9 US quarts with a filter change, other sources say 3.7 qts. My 06.5xB need just 3.5 quarts to get it exactly to the full mark after a filter change and maybe 4-5 minutes of draining/dripping.

    I will report back if there seems to be any change in MPGs after filling it properly this time. I will have to be sure to keep an even closer eye on the fill level since I no longer have that overfill "protection" against any oil used in between changes :D .

  • Hard to believe. :confuse: I am running Nitrogen in the tires and Mobil One in the motor, best I get is 32/36 HWY @75 mpg on the Suncoast Parkway here in Florida, going to Tampa international using cruise. Got 36 mpg once using Mobil Premium. Straight regular gets me 32 Hwy. If you get 40 mpg it's on a trailer :P
  • kipkkipk Posts: 1,576
    A car has about 33% more wind resistance at 75 than at 65.

    The frontal area of the car is fixed, so lets call that "Y"

    The formula for wind resistance is "Y" times Mph squared.

    At 65 mph the result would look like "Y" times 4225.
    At 75 mph the result would look like "Y" times 5625
    That is about 33% difference in wind resistance.

    Our 03- 4wd- 4 spd AT- CR-V gets 30-31mpg at 65. It gets 23-24 at 75mpg.

    Thats about 33% difference in mpg with a speed difference of 10 mph

    So, if you get 32mpg at 75, slowing down to 65 just might get you up there with

    You do the math!

    If you choose to not drive that slow, then you choose to get poorer mileage.

  • dwynnedwynne Posts: 4,018
    If you choose to not drive that slow, then you choose to get poorer mileage

    How about if I choose not to get run over driving so slow :D ?

  • kipkkipk Posts: 1,576
    Then you won't get the same mileage as the slower driver that got run over.

    No guts, no glory! :shades:

  • Mr_ShiftrightMr_Shiftright Sonoma, CaliforniaPosts: 64,482
    Dinky little engines are very susceptible to aerodynamics and speed changes, in terms of the fuel economy they can deliver. My xA's mileage would drop disastrously after 75 mph.
  • jim314jim314 Posts: 491
    Of course the aerodynamic resistance is only part of the power consumption at any speed so even if the aerodynamic component of the fuel consumed/unit distance travelled (gal/mi) increases by 33% in going from 65 to 75 mph, the gal/mi figure will not increase by 33%. The rolling resistance of the tires may increase with speed, but not proportional to the square of the speed and may actually be linearly dependent on speed. Also there are parasitic losses in the engine and drive train, etc. which may be proportional to speed and so this does not increase the gal/mi because you are covering the distance at a higher rate per unit time.

    The internal combustion engine (ICE) is actually more efficient as you increase the power output in steady operation up to about 80% of max power. The engine efficiency is expressed as a quantity called brake specific fuel consumption (BSFC) which is weight of fuel consumed per unit time per unit of engine power being developed. In "English" units BSFC is in lb/(hp*hr). An ICE has the lowest BSFC (and so highest efficiency) when it is developing 50 to 80 % of its maximum rated power.

    Since a Scion XB would require only about 25 to 30 hp to go a steady 70 mph, a 60 hp engine would be the most efficient engine which would still have some passing ability and freeway onramp acceleration. But you can see that a new Scion Xb which has a maybe 140 hp max engine is operating at say 30 hp/140hp = 21 % of rated max which is well below the optimum for best efficiency.

    Just to make clear what I am stating say that the engine in a Scion Xb has a BSFC of 0.48 lb/(hp*hr) when developing a steady 30 hp (required to go 70 mph on level ground). Suppose that the car requires 38 hp from the engine to go 80 mph and that at 38 hp the engine has a slightly lower BSFC of 0.46 lb/(hp*hr).

    So at 70 mph the engine will consume fuel at a rate of 0.48*30 = 14.4 lb/hr and the fuel consumption per mile will be 14.4/70 = 0.206 lb/mi. If we assume that the density of gasoline is 6.2 lb/gal, then the familiar mpg figure is 6.2/0.206 = 30.1 mpg

    And at 80 mph the engine will consume fuel at the rate of 0.46*40 = 18.4 lb/hr and the fuel consumption per mile will be 18.4/80 = 0.230 lb/mi. And the mpg figure is 6.2/0.230 = 27.0 mpg.

    So as speed is increased at around legal highway speed the engine is more efficient, but since it is being asked to deliver more hp, then this causes the mpg to decrease.

    NB My calculated mpg figures are lower than what is observed because I must have assumed too high a figure for the horsepower required to go at these constant speeds and/or I assumed values for BSFC that were too high. The manufacturers do not publish these figures for their vehicles and I made assumptions which however are in the range of what is the case for modern automobile ICEs.

    Note also that if you really did go for maximum efficiency and did power your vehicle with a say 60 hp engine, the engine would wear out sooner than desired unless you designed to operate at extgended periods at 50 % to 80 % of its rated maximum hp.

    Auto engines are not usually designed to do this, whereas aircraft piston engines are (e.g. Lycoming, Continental, and Rotax engines). Aircraft engines are designed to operate at say 70% to 80% of maximum rated power for extended periods of time. But these aircraft engines have a much lower max power rating per unit displacement than auto engines. A 360 cubic inch (5.9 L) displacement Lycoming O-360 is rated at only about 180 or maybe 200 hp whereas an automobile engine of that displacement would normally develop more like 300 to 350 hp. And the Lycoming O-360 as a crate engine costs maybe $25K, requires 100 octane leaded av gas (so called 100 LL, meaning "low lead"), and has no muffler or pollution controls. Compared to an auto engine the aircooled aircraft engines drink fuel, ?BSFC = 0.55 lb/hp*hr? Maybe higher.
  • kipkkipk Posts: 1,576
    >"Of course the aerodynamic resistance is only part of the power consumption at any speed so even if the aerodynamic component of the fuel consumed/unit distance travelled (gal/mi) increases by 33% in going from 65 to 75 mph, the gal/mi figure will not increase by 33%. "

    You gave a wonderful explanation! Although it went way over my head! I don't always understand exactly "WHY" something occurs. I do understand results. Example: I know that if I touch something too hot , my hand will jerk away. I don't totally understand the interaction of the nerve and brain. The result is the jerking away from the heat source.

    You say "The internal combustion engine (ICE) is actually more efficient as you increase the power output in steady operation up to about 80% of max power." and I take you word for it. However when an AT shifts into OD and the Torque converter locks, the RPM goes down the engine is less efficient, but MPG increases.

    There are many things effecting mileage at different speeds, as you pointed out.

    I know that if I drive my car in 3rd gear at 60 MPH, which would put the engine in a higher RPM mode and closer to the 80% efficiency zone, the mileage will drop significantly vs the same speed in OD. Results! Apparently the 80% thing has to do with HP vs fuel consumed. At the speeds we drive, a much lower HP is needed and less fuel is consumed .

    I know that when battling a head wind the mileage will drop. I've experienced a 3-4 mpg drop when dealing with a 10-15 mph head wind. That isn't nearly the drop that I would have gotten if I had been driving 75-80 in calm air vs 65 mph.. Seems to me it is because the car was in OD most of the time at a lower RPM than it would have been running at the higher speed.

    My next door neighbor sets his cruise control at 75 mph. His Ridgeline delivers 20+ mpg at that speed. One time on a 300+ mile trip he set the cruise at 65 and got 26+/- mpg. That is a 30+/-% increase by running slower with 33% less wind resistance and the engine at a lower efficiency. Result !

    In an above post I gave the Results of our CR-V at the various speeds. Our Pilot delivered 18+ mpg on a trip at 80 MPH. Next day, on the return trip with the same (4 person) load the mileage was 26+ at 65MPH. That is a near 44% increase by slowing down 15 mph. In this case the wind resistance difference was near 50%.

    While neither of these 2 examples show the mileage increasing exactly the same as the wind resistance decreased, it is still significant. With our CR-V the correlation was very close. My 3 examples are heavier, different shape, and more frontal area than a Scion, which surely will have effect of moving through the air. So, as you say, there are more things at play than just the wind resistance.

    Our friend Mr. dbecker6 only needs to increase his mileage by 25% to achieve a number he feels can't be obtained, unless on a trailer. I have no problem believing that by lowering his speed by 10 MPH and wind resistance by 33%, it can be achieved.

    Any way we spin it, slower speed results in better mileage. Looking at it from a cash standpoint, the person getting 30% less mileage is paying 30% more to travel a given distance. In effect paying $3.90 per gallon of fuel vs the 30% better mileage driver at $3.00 per gallon. ;)

  • jim314jim314 Posts: 491
    The results of mpg determination at various speeds must be replicated before you start drawing conclusions.

    The most efficient gear for travel at any speed is the highest gear that will keep the engine from lugging. Lugging occurs at a given rpm when so much fuel is delivered to the engine that the amount of fuel in each cylinder firing is so great that it stresses the crankshaft and perhaps squeezes out the oil film between the crankshft journals and the connecting rod bearings, mybe also the main bearings.

    Suppose you are going 40 mph on level ground, with no headwind in 5th gear of a manual tranny. So the engine speed might be 1600 rpm. You are keeping the accelerator in a certain position to maintain this speed.

    Now suppose a headwind beings to gradually build up and over a period of time increases to say 30 mph. During this time you must steadily increase the accelerator pressure to maintain 40 mph. At some point so much fuel will be in each cylinder that the car would begin to shake, but as you approach level of accelerator pressure which causes this lugging you would downshift to 4th gear to increase the engine rpms up to a level where the amount of fuel per combustion event is decreased, but the fuel flow rate (wt or vol per unit time) stays constant because there is an increase in the number of combustion strokes per unit time.
    This lessens the strain on the pistons and rings, the connecting rods and the crankshaft, but causes more frictional losses in the engine. Engine power output remains the same when you down shift if you maintain the speed. There are more combustion events per unit time.
  • kipkkipk Posts: 1,576
    Agreed! :)
  • Just bought a new xD manual trans. Getting 34 MPG in SF Bay Area, mix of Hwy and city driving. Nice car.
  • jim314jim314 Posts: 491
    This NASA compilation of formulas ( the power required to overcome various forces which resist the motion of a vehicle.

    You can see that the power required to overcome aerodynamic resistance is given by

    P,aero = 1/2 x Frontal area x coef. drag x vel^3 x air density

    So the power reqd to overcome aerodynamic drag at a given speed is proportional to the cube of the speed. However, power is the energy consumed per unit time and what we want is the energy consumed per unit distance. The latter would be proportional to the fuel use measured in gal/mile or (in the UK and Europe) in Liters/100 km. We get the energy/unit distance by dividing the power by the speed.

    So Energy/unit distance = (Constant of vehicle) x (vel^2) x (Density of air)

    From this formula we see that the aerodynamic component of fuel consumed per unit distance traveled is proportional to the square of the speed and to the first power of the density of the atmosphere.

    The EPA highway mileage estimate assumes that the vehicle is driven at a faily low speed even on the highway, something like less than 65 mph. Driving faster than the EPA assumes is a major contributor to using more fuel/unit distance, that is getting lower mpg than the EPA estimate.

    This is the basis for the often quoted "folk" statement that "air resistance at 70 mph is double that at 50 mph". (70/50)^2 = 2.0. What this exactly means is that the aerodynamic resistance consumes twice as much fuel to go a given distance at 70 mph than at 50 mph.

    But we know that mpg wouldn't double if we slowed from 70 to 50. The reason is that there are other power consumers besides aerodynamic resistance.

    Note that the constant of the vehicle is less for vehicles with low coefficient of drag and low frontal cross sectional area. A Scion Xb must have a relatively high coefficent of drag and a high frontal cross sectional area. So aerodynamic drag will be a more significant factor for it than for vehicles like the other Scions which have a smaller frontal area and CD. If a vehicle has a very low drag coefficent, like a Porsche sprts model, then the effect of increasing speed will be much less than for SUVs or the Scion Xb.
  • jim314jim314 Posts: 491
    To continue this train of thought, in the 1950s the usual manual tranny in an American car was a 3-spd operated by a long throw handle on the steering column. Some lazy people would shift directly from 1st (bottom toward the steering wheel) to third (bottom away from the wheel) at about 15 mph. I was alway told that this was that this was very harmful to the engine, but I don't know whether that was always true; it probably depended on accelerator pressure. I certainly never did it, because I could see the engine wasn't revving nicely.

    But if you did this and suddenly had to accelerate, then you would have to downshift to 2nd, which you might not have time to do in an emergency, and you would have to remove one hand from the steering wheel reducing steering control.

    Even today the operation of a standard manual tranny (as opposed to a clutchless with paddle shifters) can be problematic if say the driver is approaching an intersection in a relatively high gear (for fuel efficiency) and suddenly needs to accelerate to avoid an accident. There is a trade-off between keeping the rpms up for controllability with the accelerator pedal and with keeping the rpms down for fuel efficiency.

    I like manual trannys, but automatics are in my opinion safer, especially in city driving. I have not tried the new automatic dual clutch trannys with paddle shifters giving virtually instantaneous shifting. I'm sure I'd like it, but they must be expensive.
  • jim314jim314 Posts: 491
    You wrote: "However when an AT shifts into OD and the Torque converter locks, the RPM goes down the engine is less efficient, but MPG increases."

    This is not correct.

    You are thinking that when the rpms decrease when the car shifts into OD, that this means the engine is developing less power. The engine is actually developing the same power. The power being developed by the engine is determined by the vehicle speed, wind, slope of road, and not the engine speed in rpms. When OD kicks in the fuel flow in wt or vol per unit time (say gal/hr) stays the same, but the amount of fuel injected into each cylinder for each power stroke increases in inverse proportion to the rpms. At the lower rpm value the parasitic losses in the engine (friction between piston rings and walls, rod and main bearing friction, etc.) are reduced, which is the source of the increase in efficiency.

    The trade-off is that this increases the stress on the rods and bearings, but if they are designed to take it, then there's a net benefit. You get lower fuel consumption per unit distance travelled without engine damage that would ever come into play. That is, the engine will still last the lifetime of the body, electrical system, etc., or at least as long as the manufacturer designed it to.
  • texasestexases Posts: 9,432
    Very few cars (small ones too) get over 36 mpg at 75 mph real-world, especially ones as aerodynamically-challenged as an xB (I assume yours is a first gen?). Minor point - nitrogen will have no effect on mileage, so don't pay for it with that in mind.
  • kipkkipk Posts: 1,576
    >"...You are thinking that when the rpms decrease when the car shifts into OD, that this means the engine is developing less power. The engine is actually developing the same power. The power being developed by the engine is determined by the vehicle speed, wind, slope of road, and not the engine speed in rpms...."

    Hey Jim,

    Remember when I wrote that I don't care about the why's and wherefores?

    I still don't! The only thing that interest me is results!

    If you wish to believe that an engine running at lower RPM develops the same power as the same engine running at higher RPM, that is fine with me.

    Apparently, in your thinking, the charts that show engines developing very low power at idle and a lot more power at high rpm are wrong.

    To my way of thinking, If you were right, there would be no reason for a throttle.
    Just let it idle and shift through the gears.
  • jim314jim314 Posts: 491
    Your bring up a very good point about the torque and power curves that are widely shown in motor magazines. They never state what is the throttle position or fuel flow rate. One is evidently supposed to know that these curves are done at wide open throttle (WOT) and perhaps with the fuel flow rate stabilized at the maximum value. This must be the case because they are showing the maximum torque and horsepower that the engine is capable of producing at each value of engine speed (rpm). The torque does not just depend on the rpms, but also on the throttle position.

    Look at it this way. Suppose you are cruising with speed control set on a level highway at 70 mph when you enter a gradually steepening hill. Just before starting the climb the rpms will be a certain value and the throttle position will be a certain value, the fuel flow rate will be a certain value, and the engine power will be a certain value. (I have said I think the engine power might be about 25 hp for a compact car, but the exact value doesn't matter.)

    As you begin climbing the cruise control will gradually open the throttle to maintain speed, but the rpms will not change if the auto tranny doesn't downshift or if the driver doesn't downshift a manual. But the power developed by the engine will increase because the fuel flow (wt or vol per unit time) is increasing as it must to work against gravity in climbing the hill.

    I am not trying to catch any body in a mistake, just trying to explain the matter as I see it. I am not an engineer. I am refining this idea in my own mind as we have this discussion. An engineer might find fault will some of my assertions or might say about what I have written, "Duh! . . . What Jim is saying is so obviously the case that we engineers don't bother to state it."
  • kipkkipk Posts: 1,576

    You seem to be contradicting yourself. You write:
    >"The power being developed by the engine is determined by the vehicle speed, wind, slope of road, and not the engine speed in rpms. "

    Here you are saying the RPM has nothing to do with Power.
    (Now before you go off in another tangent, It makes no difference to me whether someone refers to "Power" as torque or horsepower. To me it is the output of the engine. Period!)

    Then you write:

    >"This must be the case because they are showing the maximum torque and horsepower that the engine is capable of producing at each value of engine speed (rpm). The torque does not just depend on the rpms, but also on the throttle position. "

    Here you are saying the engine speed does make a difference. That is a contradiction to the quote above it.

    You come up with nice symbols and pieces of formulas, and you most likely understand them. As I said earlier, they go way over my head.

    I do understand that an engine at a given RPM does not develop as much power at a closed throttle as it does at wide open throttle. However, I do believe that at most any throttle setting the higher RPM will allow that engine to develop more "Power", than at a lower RPM.

    >"You are thinking that when the rpms decrease when the car shifts into OD, that this means the engine is developing less power."

    In real world applications, YES I DO! Remember?

    The torque does not just depend on the rpms, but also on the throttle position. "

    Here is a test for ya! No books involved or necessary. Just real world. Get on a long fairly steep up hill grade with a car with Manual tranny in 5th gear. When it gets to the point that with near wide open throttle the car is barely able to maintain it's speed, make a "Speed" shift to 4th gear, WITHOUT LIFTING YOUR FOOT OR MOVING THE THROTTLE. You will find your speed will increase.

    On a flat road, With the same MT car, be at 25-30 MPH in 5th gear and floor the throttle. Now do the same at 60 mph. Notice any difference in the engines ability to gain speed? Same car same throttle usage. But even with the increased resistances of air, tires, etc., the higher rpm at 60 vs 25-30 allowed the engine to develop more power quicker, to my way of thinking.

    Drag racers with the exception of rails, fuelers and funny cars, gear their cars to be approaching the RPM red line in top gear when they cross the finish line. NASCAR, gear their cars to have them pretty much topped out on RPM for the track they are running on. Why? More Power is produced at higher RPM.

    NOTE: Some of the dragsters develop so much power that gears are not necessary. Their main concern is harnessing that power to the asphalt. The others use gears to keep the RPM high for Power.

    Now back on Topic of real world mileage. Any way we spin it, wind resistance produced by speed plays a large part in fuel mileage. Manufacturers design their vehicles to be as aerodynamically as they can to minimize that resistance. Whatever vehicle we drive will likely get better mileage at 65 MPH than at 75 MPH.

    How much difference that makes will depend, somewhat, on the frontal area and shape of the car. That includes the front, side, and rear of the car.

    People drive fast for various reasons. Some just want to get the trip over with. Some just can't stand with being passed. Some like the speed. Some are intimidated by other driver. And they are willing to pay the higher price for fuel. :)

  • jim314jim314 Posts: 491

    The fact that the motor mags show curves of both torque and horsepower reflects the fact that the motor guys know that torque and horsepower are different things. Thinking that they are more or less the same thing will lead to false conclusions about how to achieve best mpg and best acceleration.

    Power and torque are different, but are related by a very simple equation:

    Horsepower = torque (in lb*ft) x RPM / 5252.

    What determines the fuel use rate (in wt or vol per unit time) is the horsepower being generated by the engine, and not the torque value. The transmission is a torque changing device just like a lever is a force changing device. But the power coming out of it is equal to power going in minus a small loss in internal friction. The torque at the output shaft of the tranny is in general very different from the torque at the output shaft of the engine.

    See . If you are interested, I can give an analogy to the problem of selecting the best pusher for a four-man bobsled. What I am referring to is, of course, the much discussed question in the fantasy bobsled community: Should you try for Jimmy Brown or Jimmy Tayor as your pusher?

  • texasestexases Posts: 9,432
    Jim's on target, so you might want to carefully review his posts. He's not saying a car develops the same horsepower regardless of rpm. He's saying (correctly) that it takes a certain amount of power to move a vehicle at a set constant speed, regardless of rpm. Will more power be available if you suddenly choose to accelerate if you're in 2nd instead of 5th? Yes. But that's not what we're talking about here.
  • kipkkipk Posts: 1,576

    I have re read his post. As I've stated a couple of times above, a lot of that simply goes over my head. I've also expressed disagreement with some of his statements. My only concern is results.

    My present cars are achieving 30-35% better than the EPA ratings. I know from trial and error what works and what does not work. Results!

    I'm more than happy to share that knowledge with others. I feel confident that most folks on this forum are concerned with the mileage others are getting and how they can possibly improve their's.

    Formulas are not going to help most folks, as much as Real World experience.

    I've seen a formula that says a Bumble Bee can't fly! But real world says different, doesn't it!.

    As far as making "Power", again experience is a great teacher. In both practical and observation I "Know" that higher RPM are more capable of increased power than the same engine at lower RPM. As stated earlier, that is why drag racers gear their cars to near red line when they cross the finish line. The idea is to keep the RPM high and develop as much power as possible, with the engine restrictions that are imposed by rules. Of course there are always exceptions.

    Enough time has been spent on this subject. We need to stick to the topic of the forum. Jim can start a new forum "The Care and Feeding of Engines" !

  • jim314jim314 Posts: 491
    My car is EPA rated at 30 mpg highway. (Old system EPA ests. 22/30 city highway.) I have gotten 35 mpg (gas pump calcs, no trip computer) by driving steadily (avoiding passing) at 65 - 70 mph on interstate hwys.

    On a recent round 4000 mile trip, 90% of which was interstate highway or other divided highway, I averaged 31.0 mpg, but much of the trip was climbing and descending. There were long stretches in Arizona and New Mexico where I drove 80 mph (where legal limit was 75 mph), and where I got 34.1 mpg over a 702 mi stretch.

    In another car old EPA est. 17 mpg city / 22 mpg highway(which has a trip computer) I arrived at the following approximate rule of thumb on level ground, which may or may not be applicable to other vehicles, and in any case needs checking:

    For each 1-mph increase in speed over 60 mph this vehicle uses 2% more fuel to cover any given distance. So on the highway if I drive 75 mph rather than 65 mph, I expect to use 20 % more fuel. If I drive 75 mph instead of 60 mph, I expect to use 30 % more fuel.
  • kipkkipk Posts: 1,576
    >"There were long stretches in Arizona and New Mexico where I drove 80 mph (where legal limit was 75 mph), and where I got 34.1 mpg over a 702 mi stretch."

    34 at 80 is good from any angle! :) What type car and drive line configuration?

  • jim314jim314 Posts: 491
    My recent 4000 mile round-trip from Dallas to San Francisco was in my 2004 Volvo V70 base model with naturally aspirated 2.4L inline 5-cyl engine rated at 168 hp on 91 octane fuel. Roof rails, but no crossbars. Tranny is the 5-spd auto made by Aisin AW in Japan. Outbound trip was with two passengers and luggage (est 570 lb), return, driver only and very little luggage (est 230 lb total) . Tires are OE 195/65-15 Michelin MXV4+ Energy (max infl pressure 51 psi) inflated to 41 psi before trip. The tire sticker recommendation is 38 psi. Oil is Mobile1 10W-30 Extended Performance, changed once a year. The last city tank before the trip gave 20 mpg. After the trip the odo read 33,000 miles.

    The vehicle with which I took the fuel use vs speed data is a 2007 Volvo XC90 base model FWD with naturally aspirated 3.2L I-6 and 6-spd auto made by Aisin AW. I would guess that the V70 would have a significantly smaller fuel penalty for faster highway cruising. I'd guess a 1% increase (or less) in fuel consumption per unit distance for each 1-mph increase in speed above 60 mph.
  • mcmanusmcmanus Posts: 121
    At some point mileage goes down as speed increases, that's a given. But mechanical wear also increases as temperatures and stresses increase. Not only on the engine, but on suspension, tires, water pump, etc. too.

    As I drive near beautiful Detroit driving gets dangerous due to speed, potholes (our first sign of spring :cry: ), and distracted drivers. Slow up and get run over. Speed up and chance finding some sort of obstacle in front of you. Like Chicago and major east coast cities, most of the commuting is done towards the sun morning and evening, another serious safety consideration.

    The laws of physics all start piling up against you as speed increases. Stopping distances, control under wet/snow/icy conditions, driver reaction times, mechanical wear, mileage, road grip, impact forces, even noise all increase as speed increases. I vaguely recall a reknowned physicist saying that automotive travel over 50 mph isn't practical on a planet this size. Not quite sure what he meant by that, but its nutty when you can track your daily commute on a 12 inch globe. I kept remembering that idea as we suffered through the years of the 55 mph national speed limit.

    In Europe displacement and/or horsepower are taxed, in case $10/gallon fuel isn't enough of a discouragement. When ground travel is too slow, people move to flying, and pay for that privilege too. Either way, North American drivers are quibbling in comparison to the more expensive options or the safety issues involved. Maybe with the two oil men out of the White House, we'll be able to hold off $4 and $5 per gallon gas for a bit longer.

    I'm interested in this discussion as I'm seriously considering purchase of an '08 xB. I do mostly rural driving (two lane and freeway), so I'm hoping for a 30 mpg average. In any event the Edmund's TCO is a very low $0.43/mile for the current xB. I like the chair like seating, low purchace price, and no haggle pricing too. Easy for Dad (at 83) and me :blush: to get in and out. Can't tell you how many hours wasted playing irksome pricing games with dealers, just to walk out in fustration.

    Yes, I'd like the armrest to be wider, but our Sienna's armrest is almost as bad and we've lived with that for 7 years. I'd like a conventional gauge layout, lower window sills, lower engine speeds at highway speeds, and more than just one intermediate wiper speed (my current ride has 10). Honestly I wanted to like xD, but it won't hold a set of golf clubs without folding down a back seat and the xB's 2.4L engine is better known to us and our mechanics. '09 Corolla was another consideration, but the price is higher for a bigger footprint that has less space inside with that same more efficient/less well known engine and price haggling compared to xB.
  • jim314jim314 Posts: 491
    I don't revel in exceeding the speed limit, and only do it under conditions of low traffic and good road conditions. I recognize that higher speed always reduces the safety margin for an unexpected maneuver. On my recent trip I exceeded the speed limit by 5 mph because most of the other vehicles were doing likewise and I had long distances to cover in specific time intervals because I was sleeping in my vehicle at public campgrounds which closed for the night at about dark. There is always a higher fuel use per mile above say 55 mph, but for the 1735 miles from Wasco CA to Dallas TX (with side trips) I used 52.8 gal of 90 to 91 octane fuel so I averaged 32.9 mpg (driver only and very little luggage), even though I was going up to 80 mph when the limit was 75 mph, and when it was in my judgement "safe" to exceed the limit by 5 mph.

    The upright seating position of the Scion Xb is a great plus, and I wanted one of these at one point, but didn't buy it because my old car (1991 Dodge Spirit 2.5L 5-spd) was reliable and fuel efficient. Then I got a 2004 Volvo V70 as a hand-me-down so I'm released from car shopping for the indefinite future. An Xb would be expected to have a significant fuel economy penalty for speeds over 65 mph, and I would be less likely to do it than in a more aerodynamic vehicle.
  • nthenthe Posts: 414
    I just bought a tC last wed, and my first tank got about 27.7 mpg (about 400 miles on the car).

    oh and as a side note, i picked up the car on wed afternoon, then friday night we had a bad storm with hail, and now my brand new car has dents all over it. what a very sad, sad sight right now. :(
  • dwynnedwynne Posts: 4,018
    I had a new Ford SVT about 6 weeks when tornados came to town and the resulting hail did a number on my new car. I took it to one of those "Dent Doctor" type places and they fixed it good as new. There is a limit to what they can do, but they were able to fix mine.

    If they say they can fix it, I would strongly advise waiting until their business has dropped off from the storms. Insurance paid for my SVT to be fixed, but I went back later with another car and had a bunch of parking lot and other dings fixed for a FRACTION of the cost of the insurance paid repair. Waiting for them to have less work and telling them the money was coming out of my pocket netted a better price. In your case, your insurance should cover it like they did mine - but due to all the claims they just wrote me a check for the repair.

  • dwynnedwynne Posts: 4,018
    Have just under 10k on the clock now, automatic transmission. Recently changed the oil and made sure it is properly filled - no overfill. My wife took the box on a 450 mile highway round trip over the weekend and averaged just over 31mpg.

  • nthenthe Posts: 414
    yeah, insurance is taking car of mine, luckily i only have a $100 deductible for comp.
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