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Diesel vs. Gasoline
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Appreciate the feedback. will try the fuel line to see if its sucking air and check the fuel filter. I'll get back to you and let you know if this helps. Thanks again guys!!!!!
Thought I would spark some conversation.
Way back in engineering school or when I was co-op student at GM, I learned that at wide open throttle, the most horsepower per unit of fuel was found at the following conditions.
For spark ignition engines: Best brake specific fuel consumption was produced was at their torque peak.
For compression ignition engines: Best brake specific fuel consumption was at their horsepower peak.
So, relatively speaking, spin a diesel fast for best fuel economy and a gasoline motor slow for best fuel economy when running them wide open.
What a diesel CAN do is run all day at its max rpm. Diesels are very happy to hit their redline and stay there. A spark ignituin engine can only hit that redline as a peak, otherwise you can literally hear the wear in the engine. Unlike a gasoline engine, I can hit redline in overdrive with an automatic in my truck and keep it there (95 mph). I have never seen a gasoline engine that can sustain redline in overdrive, regardless of transmission.
the diesel can hold redline overdrive because of the superior torque. a gas engine with enough torque @ high rpms, should hold redline. i wonder if the new GM motors can do that since their torque at 5000 rpms is only a few percent off peak.
i going to disagree with you about the diesels running at redline all day. thats not totally true. SOME diesels are designed to run at redline, but most are not. most industrial diesel makers make the same engines in classes. Caterpillar i know does, i'm sure cummins does too. Take some random example, say a large v-8 caterpillar that has 1500 ftlbs of torque. you can get a class A (300 hp), class B(350 hp), class C(400 hp), etc. you'd think the class C would be the most powerful engine, right? the things is, the Class C is only rated at 400 hp momentarily. the engine is not designed to sustain the high rpms it takes to get 400 hp. The class A engine is the one designed to sit at 300 hp all day long. but even then, that is NOT REDLINE. Redline means danger. that means valves are not keeping up with the pistons, endangering piston slap. redline means rod bolts being stressed to a max are being stretched.
i've seen hard headed oil field managers not heed advice and try to put some high horsepower class C motor on a generator application, set the governor to run at constant high horsepower. then they wonder why their $50,000 engine blew up the next day. it was designed to run like that. diesels designed to run at the higher rpms have sturdier valve trains, a little different timing (sometimes), bigger rods and mains, and bolts.
as for today's pickups, i can almost gaurantee that they are not over designed to sustain high RPMs.
One question: was your mileage there recorded at WOT? If not, it doesn't apply to the previous point. Then again, mileage numbers at WOT aren't useful all that often in vehicles...
horsepower (at a specific rpm) = torque (ft-lbs at the same rpm) times rpm (revs/min) times 2pi divided by 550 (ft-lbs/s) divided by 60 (sec/min).
short form: torque * rpm / 5252 = horsepower
So, torqu(ie) motors are motors that produce LOTS of horsepower at low rpms.
So you can't really say 'torque gets you up the hill and hp is for....'
If, at a specific rpm, your engine makes more hp at wide open throttle than is needed for climbing the hill you will either: accelerate, or be able to lift slightly.
Great stimulating converstation guys!!!
An over-the-road truck diesel is governed so low, that it almost has to run at that max end on the highway. Cummins, Cat, and Detroit usually have engines that stop at either 1800 or 2100 rpm. With a standard size tire (usually a 12x22.5 or metric equiv) and a 3.70 axle, 2100 rpm would only give you 70 mph in direct drive, and we all know semis will cruise at more than that all day on the interstate. Overdrive would only yield a few more mph.
Generators are kinda apples-to-oranges, in that there's often not much requirement to change engine speed. Take as an example the 2 cylinder diesels that run trailer refrigerators. You turn 'em on, and they just run. A vehicle engine is frequently risng and falling through its operating range through throttle, shifting, etc.
Your points are well-taken, but having put plenty of miles on both diesels and gasoline engines, I'll give the diesel the edge in high-rpm running.
markbuck,
Your formulas and theories are correct, but to say the more-torque motor produces lots of hp at low rpm is accurate, but not relative to real-world use. I'll compare my current truck to my last one:
Ford F150/302 V8 185hp/270 lb-ft, 4800 lbs
Dodge Ram/Cummins 180hp/420 lb-ft, 7000 lbs
Because diesel trucks tend to weigh so much more, you won't notice the hp advantage at low rpm - they are using their torque advantage to get rolling.
but diesels don't turn lots of horspower at low rpms. just think about what you said. hp is torque times rpms, so how could hp be especially high if the rpms are low? The torque is high, but you don't get any kind of higher hp numbers until you rev it close to 3000 rpms, where torque AND rpms are high, (thus the product, rpms*torque= high number).
i've done dyno tests on many a diesel, and they're all the same.
to me, hp doesn't really mean anything most of the time. a torque curve is a true measure of an engine. hp power numbers are just a mathematical optimization of 2 numbers multiplied together.
Kcram
If you're thinking like I think your thinking (??), i agree. given a gas motor that must run at 2500 rpms on a 70 mph trip as opposed to a diesel running at 2800 rpms on a 70 mph trip, i'd trust the diesel for longevity.
but if we're talking who's going to last longest at 4000 rpms, well, BOTH trucks better have bike in the bed....
That's why I went with the short stroke 4.8L motor in my new Silverado ;o)
yep, we're on the same page
markbuck,
for longevity, I'll take my long-stroke Cummins 5.9L straight six over the Chevy short-stroke 4.8L gas V8. With an average of 300,000 miles to overhaul in medium-duty trucks, regular maintenance should keep my oil burner going well after the truck is a rust pile around it.
I really think that an average of a couple of hundred thousand miles is about as much as anyone can expect from a vehicle driven short trips, back and forth to work, started ten times a day. Driven in over the road conditions would substantially improve the life of any type of engine.
Kinda like light bulbs........
On my 7.3 L '92 F-250, the glow plugs were easier to replace than most spark plug engines I've worked on.
On hard starting problems:
The easiest way to determine the cause is to plug in your engine block heater over night. If the engine starts easily, the problem is probably either several bad glow plugs or the glow plug controller. (Ford admits that the controllers are problematic. Replacement is $200-$300 at a dealer.)
Glow plugs fail in one of two ways; shorted or open. A single shorted glow plug will make any vehicle hard to start. To test glow plugs use an Ohmmeter. Disconnect the connector from the glow plug and measure to ground (engine block). Less than one Ohm, replace the plug. Over 5 or 6 (I can't remember exactly.) Ohms, replace.
Finally the glow plug controller should provide between 8 & 9 volts to the glow plugs. (If I remember correctly it's the brown wire.) The controller works by sensing the current to the glow plugs and infers temperature. It's a kludge, but it works.
Don't be shocked at the price of glow plugs. The last time I bought three it was in the $70 range for all three.
Rich
FYI, you can get OEM motorcraft glow plugs at autozone for around $7. Went through a glow plug controller on my truck along with fixing a wiring harness. Ford says don't get water on the controller. Tried not driving in the rain and moving to AZ but...... ;o)
Looking forward to my new chevy 4.8 minimal maintenance V8 that I can even drive in the rain and park at the ski resorts in Colorado without worry of no starts.
I drive 120 miles round-trip to work everyday. All highway I might add. Here in Ohio we get some lake-effect snows and I would like to purchase a 4x4 truck. I also live on a farm. The problem that I have with the gas engines is the fuel economy. I am entertaining buying a diesel due to the fact that I believe that my long commute would give the engine a proper workout, and much better fuel economy. Am I correct in believing this? If so, could some of you Dodge and Ford owners give me a clue as to the actual fuel economy I might experience?
I am trying to see if it would be in my best interest to buy a diesel full-size truck, or just stick with a S-10 with a V6. I know the price difference, but I am willing to pay more for the diesel full-size if the operating costs would be cheaper for me considering only the full-size with a V8 gas. The extra room would be nice too, as I am 6'4" tall. The truck would mostly be driven unloaded, except for the occasional load of wood or an ATV.
Any input would be appreciated. Thanks.
The new SuperDuty Pickups from Ford sure are nice though.... My buddy just got his Crew Cab F350 and the back seat is almost as comfortable a ride as my '88 Crown Victoria was when it was new.
i don't see how a diesel can help you out cost wise. You can buy a full-sized half ton pickup with a V-6, and you will get 18-20mpg in town, and 23-24 highway (chevy numbers, ford should be close to those). that truck will cost you about $22K decked out.
or you can get a diesel, that will get between 17-20 mpg all the time, and pay close to $30K.
If you're driving highway miles, you'll be getting better mileage out of a V6 in a smaller truck than you will the diesel in a larger truck.
even if you get a midsized v-8, you'll get about 18 mpg highway, and you'll have more power than it sounds like you'll ever need (since you never pull, right?). that 2 mpg difference isn't going to pay for the $5000-$8000 difference in the cost of the truck.
don't forget, diesels are MUCH more expensive to maintain that gasoline, these days.
gas engines are more efficient now than ever. if i was in your situation, i'd go with v6 in a halfton. plenty of room for the weekends, great economy, and plenty of power if all you do is haul light loads and drive down the highway.
gasoline $.77/gal
diesel $ .99/ gal
jug of windshield washer fluid, tire rotation and other check ups plus a free courtesy car while your car is being serviced.
So I went over to the service desk to inquire about the program and I was told for my diesel it would be $199.00 for one year or $649.00 for the four year package. I couldn’t get my wallet out fast enough as I travel over 100,000 KM a year that’s 20 oil changes a year at $65.00 a pop is $1300.00. I paid for the four year package and I average that I will travel 400,000 KM over four years and that’s 80 oil changes at $65.00 for a total of $5200.00 and I paid $649.00 for the whole deal!
Just imagine if I hadn’t seen the pamphlet on the counter I would have missed out on this deal, I see it as the $4551.00 that I just saved on oil and oil filters paid for the diesel engine right there. I wonder how many dealers actually have this type of service and nobody lets them know about it .
Thats awesome, I wonder if my dealer has the same plan or similar. The only down fall for me is the dealer ship is almost 30 miles away. It is a little inconvenient to travel there unless for something major.
I did the last change. The filter costs about $11. and I'm buying the oil by the case in gallon jugs at Sam's Wholesale for I think $25. So I can do it for about $25 or so per change. But the hard part is disposing of the oil.
Mroffshore
Oil changes every 5000 miles. Filters ran as cheap as $4 and later up to $6. Oil was less than a dollar a quart. (In quantity, Penzoil, several cases of gallons at a time.) A couple of quarts of Slick-50 or T-Plus ever 25K miles or so. The belts every 25-30K until I got smart and bought Goodyear belts. They were going strong at 60K miles.
By contrast, my wife's '91 accord had the 30K miles service and a minor oil leak. The camshaft timing belt was also replaced for a bargain at $800.
DMW,
If you're commuting 120 miles you'll learn to love the diesel. On the road you'll do about 40% better mileage than a like gasoline vehicle. (7.3L PSD vs. the V-10.) Remember your're driving a vehicle that is better than 3 tons in weight. The 3.73 rear end ratio is a MUST.
You'll also find the diesel is much easier to drive. The torque makes the truck feel as if it would pull anything. With my '92 7.3L I did a thrice monthly commute of 330 miles one way. (Stayed for three days and then returned.) After about the third or fourth trip, I realized that I never wanted to do that with a gasoline vehicle. The sheer joy of the torque made me sorry that the commute was over. Once you drive a diesel you'll never go back to gasoline.
Rich
You have all been a big help. I have been to several dealerships that seem to know nothing about what they sell, except the profit. I am slowly finding more about the diesels. I have been on Cummins' and Navistar's web sites, and even been to a couple semi-truck dealers asking questions.
I am planning on buying my truck around May or June, so I have a little while to think about it all. I'll try to update you if I discover any new important info.
Oh, by the way, a friend of mine has a 1996 Ford F-250 with the 7.3 Powerstroke TD. I asked him if he had any injector problems. (One of you guys mentioned problems with the Powerstrokes a few responses back.) He claimed that only the 1997's have been having serious problems with bad injectors. Anyways, hopefully they have the problem fixed by now. I am still not sure of whether to go with Dodge or Ford, but I guess I've got a little while to decide.
Those non turbos were good motors and cheap to maintain. You could rebuild a fuel pump for less than $400, go thru each injector for less than $50 each. everything was mechanical, simple.
now move to 1994. everything is computerized. no longer simple. no longer cheap.
I noticed the same thing. After two oil changes the oil never really blackened. I was very suprised then again I never had anything to compare it to in terms of another diesel.
Mroffshore
My '86 6.9L also blackened the oil very quickly. As cdean suggests, the new computerized engine may have a lot to do with it.
Rich
Caterpillar, Cummins Engine, Detroit Diesel, Mack Trucks, Navistar International, Renault and Volvo were involved in a US Federal lawsuit claiming the engine makers intentionally equipped 1.3 million diesel engines with computer chips that allowed them to pass the EPA's 20-minute emissions tests.
I found this information in a Fire Engineering magazine (Dec 98) and also in a USA Today
article from 23 Oct 98. I have downloaded the article from USA Today (attached below for
your reading pleasure, and just to save you a dollar for the USA today download.) I also
searched the US EPA site, but all I could find was legalistic Mech Eng stuff (I'm "only" an
Elec Eng) that did not seem to apply directly. I've looked at the recalls for 98 pickups at
http://www.alldata.tsb.com/TSB/98_mk.html and can't see anything referring to a recall of diesel engine control chips. It could be that the chips were only in the big rigs, but who can tell for sure.
Question: Has anyone heard about a recall to replace the chips on diesels?
******************
USA Today Article:
******************
Emissions chip draws fine
By Earle Eldridge
Fri., Oct. 23, 1998
FINAL EDITION
Section: MONEY
Page 1B
Seven engine manufacturers must pay fines and improve pollution controls as part of a $1 billion settlement of allegations that they cheated to get diesel truck engines to pass
emissions tests.
''These seven companies sold engines . . . designed to defeat federal anti-pollution controls,'' Environmental Protection Agency Administrator Carol Browner said Thursday.
The agreement settles a federal lawsuit claiming the engine makers intentionally equipped
1.3 million diesel engines with computer chips that allowed them to pass the EPA's 20-minute
emissions tests.
When the engines were on the highway, the chips -- which the government called ''defeat devices'' -- made the engines emit three times the limit of nitrogen oxide air pollution.
Attorney General Janet Reno called the settlement, in which manufacturers denied wrongdoing, ''one of the most important environmental enforcement actions in American history.'' She said it would reduce smog-causing emissions from large trucks by one-third over the next five years.
The engines were used in vehicles ranging from large pickups to tractor-trailers. The companies: Caterpillar, Cummins Engine, Detroit Diesel, Mack Trucks, Navistar International, Renault and Volvo.
The companies must pay $83.4 million in fines and $110 million on projects to reduce pollution.
An additional $850 million will go toward improving emissions on new engines and removing
the devices from 1.1 million trucks.
Engine makers said they didn't violate any laws but agreed to the settlement to avoid costly
litigation.
I need some information on the 6.5 chevy turbo diesel--any experts?
I am looking at a 95 Silverado with the 6.5 diesel turbo...I am planning on pulling a 30 foot or so trailer--so I like the concept of the diesel, however, I am dumber than dirt on this engines history. Who makes it--what is its reputation, what kind of milage can I expect, and finally--is there a higher or lower anticipated maintenance cost as compared to the 350 chevy (or 5700 as the current namesake goes).
Id apreciate any info that helps me decide on my truck.
I'm not an expert by any stretch of the imagination, however I am an educator and I feel you should really educate yourself regarding the Chevy diesel.
I have read the block that Chevy used was essentially a gas engine block and the motor was some what unreliable. I can't say for sure but you should investigate further.
If your going to buy a diesel buy the Ford or Dodge. They are very good and you will have good success with either. I have the Ford PS and love it.
Just a suggestion, find out all you can before you buy the Chevy because you may be sorry if you do.
Mroffshore
GM has pulled all of it's new truck stock from the dealerships to redesign the engine. The dealerships wouldn't even carry them in Texas because of the problems. If GM has no cofidence in their own engines, I wouldn't either.
Have 96 powerstroke with 40000k have had problem starting in last couple of weeks. need help.
"[The] newly designated gold-standard in
full-size trucks: the Ford Super-Duty"
But I wouldn't recommend it, the test wasn't very well conducted IMO. Drive both, talk to owners, and come up with your own opinion.
That wasn't the whole question, though -- just thought I'd clear up that quote. Personally, I really like the V10 -- and my last engine was the 7.3 diesel. It has plenty of power, but I've only towed about 7,000# up shallow hills. Then again, I did it in cruise at 70mph and it never even downshifted from OD (4.30 gears). I'd pick it out of the three unless doing constant long-mileage trips (over 500 miles) where I might go with the Powerstroke diesel.
Thanks Again. Jeff