Re: Buying a diesel truck

Posted by jdemaris on May 23, 2007 at 18:28:44 from (69.67.230.151):

In Reply to: Buying a diesel truck posted by Lincoln on May 23, 2007 at 16:49:16:

There is no doubt that a "ladder-frame" straight block, such as the Cummins in-line 6 design, is a inherently stronger design that a typical V-8. You cannot count Detroit or Cat V-8s because they are NOT lightweight automotive diesels - they are heavily reinforced.
That all being said, all that counts is that the engines will last as long as the trucks.
Ford 6.9s/7.3s light-duty diesels, and the Cummins 5.9 a medium duty. Engine life is projected in HD engineering with a "B" rating.
Cummins 5.9 has a B10 rating of 250,000 miles. That means only 10% do NOT make it that far. 5.9 also has a B50 rating of 350,000 miles - i.e. 50 % make it, 50 % do not - without major repairs.
Ford IH 7.3 has exactly the same B50 rating, but is not considered "medium-duty" because it does not have replaceble sleeves. It's bigger brother, the DT466 does have sleeves and has a B50 rating of 375,000 miles. The new Ford IH 6.4 also has a B50 rating of 375,000 miles.
The GM 6.2s and 6.5s never got B ratings, I assume because they were never intended for heavy use. But . . . the Isuzu straight-six-cylinder GM uses in bigger trucks has a B10 rating of 410,000 miles and puts out 810 lb. ft. of torque - that's pretty impressive.
The GM Isuzu Duramax V-8 has a B10 rating of 220,000 miles.
In regard to cubic inches versus weight, a GM 6.2 or 6.5 weighs 650 lbs. A Ford IH 7.3 weighs 860 lbs. A 6.6 Duramax weighs 836 lbs. 5.9 Cummins weights 1,036 lbs. Obviously, the 5.9 has the most weight per cubic inch, whereas the GM 6.2/6.5 is the lightest.
In regard to fuel mileage, I can tell you my own experiences. From what I've driven, and of other trucks I know of, the Dodge Cummins has been the best with fuel mileage - often 19-21 MPG with a 4WD truck on the highway. I've got three neigbors with Duramaxs - Allison trans - and the best report has been 18 MPG. My one neighbor has a rusty 1993 Dodge Cummins that consistently gets 19 MPG highway. His 2005 Durmax with Allison has never done better that 14 MPG. He loves the Durmax for pulling power, but curses it for fuel mileage.
I've got a 85 Ford F250 4WD ex-cab, 4.10 gears, C-6 trans and 6.9 diesel and it has never done better than 14 MPG on a highway cruise. Also have a 94 F250 ex-cab 4WD with 4.10 gears and overdrive-auto with 7.3 turbo, and it can get a best highway mileage of 15.5 MPG. Also have MANY 6.2 diesel trucks - the best has gotten 25 MPG but is useless for heavy towing.
Farmer next to me has a Dodge Cummins 4WD high-output 5.9 diesel - one year old. He gets 18 MPG highway.
I'm sure you'll get other reports - just take everything with a "grain of salt." When I bought my first diesel Suburban - used - the owner told me it got 30 MPG. Found out it got a best of 19 MPG. When I bought my first Ford F250 with 6.9 diesel - the owner told me it got "around" 30 MPG - found out it gets a best of 14 MPG - and I'm not a hard driver.

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