2008 big Three Diesel performance

[neighborman]

My December 2007 issue of Popular Mechanics had an interesting article that compared the Powerstroke, Duramax and Cummins. All three trucks were 1 ton crewcabs. While P.M. asked for duallys, GM didn't have one just then, and provided a SRW.

They ran each truck in a 300 mile loop to check fuel economy, acceleration, braking, etc. First they made the run solo, and then with a 9120 lb trailer attached. The Ford's mpg was 11.24 and 7.60. The Dodge was 13.00 and 8.7. The GMC was 18.26 and 10.50. Being pretty much of a Ford man, I was disappointed at the data.

While the axle ratio on the GMC was 3.73:1 and the Ford and Dodge were 4.30:1 and 4.10:1 respectively, the mpg's still seems like a big difference in favor of the Duramax. The Ford was significantly heavier than the GMC or Dodge, and it might be rated for heavier loads. (don't know about that though)

All things considered, I think I might have to give the GMC/Chevy a test drive whenever I am in the marked for another truck. Anybody have any personal experience about this?

[Broome101]

MPG with different rear ratios make huge differences in MPG

[Delaine and Lindy]

When Ford Super Duties went to the 4.88 rear gear it killed the fuel mileage for the 6.4 it has to turn so much highter RPM's. And then add the DPF emissions system which just makes it burn much more fuel. Its just a bad combo. However the F-450 has awesome torq with the rear gear being a 4.88. You just have to give something up, if I were buying a F-450 I would go no higher than a 4.30 gear, and if I could get a 3.73 I would go with that. Higher RPM means more wear on the Engine and it will burn more fuel. We are running 3.73 gear and turn abour 1600 hundred RPMs at road speed. The F-450 than I road tested turned about 2500 RPMs at road speed. Our Chevy 4500 turned 2500 RPMs at road speed. But I also got 10 mpg towing the Cambridge at 68 mph (No DPF). I really believe the EPA nuts have killed the fuel mileage on the Diesel engines for what I don't know. Life is good, what a country... GBY...

[BB_TX]

Had the GMC been a DRW with higher ratio rear end, it probably would have been more in line with the Dodge. But yes, the general reports of the Ford 6.4 seems to be something less than desirable fuel mileage.

[richfaa]

Even with a defective DPF we got better MPG than 11.24 solo and 7.60 towing the 3400 down here Via 1-71 and I-75 to Florida. That is with a 4:10 diff.They would have to throw about 800 lbs of bricks in the back of the Dodge/Gm in order to get a fair MPG comparison. I put no stock at all in these so called comparisons no matter what the brand ranking is. The new diesels ARE less mpg efficient because of the new emission standards. It is my opinion that the Cummings diesel is more MPG efficient than the other two. Considering what my F-350 weighs loaded for towing, full fuel and two folks aboard,,,9212lbs.. we are not doing bad at all in all categories. I don't get it..the Ford weighs more yet folks are surprised that it gets less MPG..Duhhhh... Since the DPF replacement and re-tunning we are doing in the 15's driving around here and did 18.6 on the Florida tkp to Pompano Beach last week.

[skypilot]

I remember reading that the change from 3.73 to 4.10 gears would result in about a 10 percent decrease in mileage; from 4.10 to 4.30 about the same so if it is linear, that would be 20% decrease on account of the gearing.

[neighborman]

Rich, I know that the Ford weighs more, and is geared lower, so I'm not at all surprised that it got lower mpg's than the Duramax. What does surprise me is the degree of difference. (If your "duhhhh" comment was aimed at me, I'll attempt to take it in a good natured manner.)

My real purpose for bringing this all up is to get anecdotal evidence from folks to see if the reported story is the real deal. Sounds like you're having better results since you got your 08' fixed. Question: Given your experience thus far, would you still get the 4.10 rear end, or another, like maybe the 3.73? I know from earlier posts that your old truck had a lower ratio, which I assume was due to the torque difference between the diesel that was available and your V10.

How about some 2008 Chevy/GMC and Dodge folks- how are your rigs doing?

[Pete Hanson]

It seems to me that the two trucks that were dually's were at a disadvantage since the more tire contact with the road you have the more resistance there is. Not to mention any added weight. My Dodge is a 3/4 ton non-dually but I get significantly higher mpg than this report shows both in solo or towing mode.

[HamRad]

I have one of the 7.3 PSD 450s with the 4.88 gearing. I really expected a large decrease in my towing mileage. I went from a 7.3 250PSD with a 3.73. But I ended up getting just about the same mileage. Right at 10 mpg. But what a difference in shifting. The 250 was always trying to find the right gear even with the least little change in road grade.

The 450 does not have that problem. It's almost as good as the Tow/Haul feature on the later models. Anyway I've very happy with the 450 and the 4.88.

HamRad

[OntMont]

Those GM figures seem pretty close to my experience with a Chev 3500 DRW. 3.73 is the only rear axle ratio available for the Duramax/Allison, but the rear end is only part of the total drive train. The 6 speed Allison probably has a lot to do with the milage.

[richfaa]

neighborman.. Not directed toward you at all but toward the folks who write those meaningless articles and think we are stupid enough to not recognize the difference. Sorry..never mean to offend.... We were not able to order the truck from the factory. If we had we would have ordered the 3:73's. The 4:10 was the best they could find and we would not accept the 4;30's in the diesel. We did have the 4:30 in the V-10 for as you say, the added torque. A defective DPF has a huge impact on the all over performance on these new diesels. If you have any signs of black soot in your tail pipe you have a bad DPf and your truck is not running right. IMO, which means nothing, The Cummings is the best suited diesel for towing but the truck configuration did not meet our needs. We really liked the 08 Durimax and test drove one many miles. As mentioned we did not have the time to order any truck from the factory..We could not find a GM/ Chevy close to the configuration we needed and Ford offerd a much better deal..We have had 3 Gm tv's and 3 Ford Tv's..thay all did exactly what we expected from them.

[TLightning]

You would think that if they were going to run a true comparision, they would have waited to get a GM dually, and have gotten all three trucks with the same rear end. The rear end would have to be 3.73 because that's all GM offers. And, as noted above, Fords are very much heavier than GM (about 800# for a 3/4 ton)...don't know about Dodge.

[tbhd2]

It depends where they obtained the trucks from used in the comparison. Most of these test are done with vehicles provided by the manufacturers. Some are not really as you would buy one off a lot. They tweak them a little to perform a little better. They're still stock but not as you would buy from a dealer. The information you get from these forums are so much more accurate.

[hazmic]

Two things here.
1 How many miles on the trucks? Were they even broke in?
2 ULSD will not give as good of mileage as the LSD. This could be a good reason why we do not get the mileage we use to get.

[clutch]

As usual with these tests the vehicles were not even close to each other in configuration. Dual wheels and lower gearing versus single rear wheels and higher gears just make it an observation not a real comparison. Why do they even bother with "tests" like this?

[BB_TX]

Interesting article about Ford modifications to improve their fuel ecomomy. Going to 3.55 rear ends.
http://www.pickuptruck.com/html/news...n08change.html

[Steve and Brenda]

Thats the mileage I get in my Silverado with a heavier tow load.

[neighborman]

Lots of good feedback here. Thanks a lot! BB_TX, I followed the link you provided; it looks like Ford may be getting the message about MPG.

I pull a 2002 3670RL, which is pretty heavy, with my 2000 F350 6spd manual, 4.10:1 rear. On three round trips from Lebanon, TN to Casa Grande, AZ, I averaged from 9 - 10 mpg. Last summer, I took a trip from Lebanon thru Va Beach, VA, thru Philly, thru Boston, Bar Harbor Maine, Jamestown, NY, and then over to Rich's neck of the woods, Olmstead Falls, Berea, Middleburg Hts Strongsville areas of Ohio to look up some of my roots, then home. I got 10.7 mpg over 4000 miles, with only about 200 miles of it solo. Most of the fuel I used was ULSD, but I used an additive, so maybe that made a difference, don't know for sure.

One thing I do know, I have to plan my trips a bit more now with fuel up there so high. We're headed for AZ again as soon as my new grandson is born (any day now), and it will cost about three times what it did the first time we made the trip in 2002.

[quarrles]

I really like my choice of a 2008 CHevy 350 with the Duramax and Allison 6 speed tranny DRW 4X4 because it is just what I wanted in a new 350 dually. My experience with the mileage is not germain because we all load and drive differently. I hope that all are happy with their choice of TV and I do not consider your choices to be less or worse than mine , nor do I consider you less intelligent because of your choice of TV. With diesel prices being as they are one could question all of us about choice of TV and expense of our hobby.

Happy camping...John

[PowellsMonty]

My 2200 mile 3.73, 6.4 F350 already gets better milage than my 2002, 7.3, 3.73 did.
Consumer Reports is another one not to belive either.