According to the local Kenworth salesman, the truck I'm looking for (t800SH) only ever came with the ISM/c12 or the EGR ISM/C13 in emissions years. I do not want an EGR/ACERT engine so I'm looking for the former two.

Which is better and why? The salesman suggested the ISM, in 425 HP trim. He said it is a very good engine.

Why the prejudice against the C12 or C13 Cat?

We've got a whole bunch of those in the fleet of dump trucks where I work and they kick *****, no major mechanical problems.

Now, if you're gonna use the KW for OTR, you may want the C15.

We've got C15's in our heavy haul tractors and those have also performed well.

When I said "former" I meant C12/pre egr ISM.

c15's aren't available in the t800SH. I wouldn't consider them either.

Well, excuse me!

Don't worry buddy you're excused!

So you think the C12's are good motors? I know someone with one and he's very happy.

I would have no problem getting an EGR version Cummins. Just disable the EGR like I did on my ISX and gain about 1 mpg better fuel mileage, less wear and tear on the engine (oil samples look better), and engine runs w...a...y cooler, even on a warm day with the AC on and under a good pull, it never gets above 190-195F and the fan hardly cycles anymore... only if sitting in traffic or idleing. Recently pulled about 43,000 lb payload over the WV turnpike and then on hwy 460 into VA and the fan never had to cycle once pulling those hills with the AC on.

The C12-13 cats are a VERY good motor can and will out pull a Cummins and will also out last them when it comes to time before an inframe. There is a decent sized company over 200 trucks and all he has is C-13's in his fleet some are approaching 1million miles in Bulk Service and still have not been inframed yet. Only issues he has were a couple did puke some injectors but that can happen to ANYONE. MPG's are in the mid 5 range loaded with tanks with the T-800's 6+ coming back empty.

The C-12 and C-13 are both very good engines, BUT they are considered small blocks, for OTR and maximum gross type of loads you are better off with the big blocks, C-15 or ISX Cummins.

Remember you can always drive a big engine slowly and conservatively, rather than have to run a small engine at its limits.

Personally I'd rather have the power and never use it than not have it when its needed, lots of real world testing has proven smaller is NOT always more economical.

I've been driving a C12 for a year now, pulling flat, curtain van & tanker. IMHO;

1. It's been dead reliable. I'm at almost 450K & as far as I know it had no probs under the previous drivers either. I add 1-2 gallons of oil on a 15K cycle.

2. It feels & sounds like a CAT motor, which I like, it has the fly by wire throttle feel which I don't like.

3. I have gotten 7 mpg once, with a light load in a curtain van. At 80k, with some hills I will get down into the low 6's, maybe even high 5's. With a flat (I'm usually d/h one way) I probably average 7. If you want I will check for more precise #'s. One thing I find interesting is that I am now on a dedicated tanker haul, running the exact route & loads as one of our other trucks. It has a pre-acert C15, 475 HP, 1750 torque. I pulled flat with it for a couple of days once & it just might be the best performing motor I've ever driven. On our route he uses the same fuel as I do. It kind of shoots a big-azz hole in the idea that you get better fuel mileage from less power. Of course getting our mechanic to look at anything like a potentially leaking air cooler is impossible. If the truck moves I will drive it.

4. We've got 2 C13's, they out-pull me easily. So does almost everybody else. I think if you want a C12 you need a 13 speed and a rear end ratio that keeps you at 14-1500 RPM at your desired cruise speed. Under 1500 & you will down shift to pull a big overpass with a curtain van. Mine does not feel happy under 1300, I just can't keep my foot in it down to 1200 like with a big block. Of course a 1500 cruise will likely lower your mileage #'s too.

I hope this helps- any questions, feel free to ask.

I picked up a load of 44,700 lbs in Texas the other day and took it to Montreal, Quebec thru Louisianna, TN, OH and then NY. Did 60 MPH all the way and my Dyno-tuned CAT C15Acert (550 HP at 1,425 RPM, 2000 lb-ft torque) did 6.4 mpg. These are U.S. gallons measured at the pump (the computer showed 7.1).

By the way, I threw out the ACERT muffler last summer and put a free flow one. Did emissions this year and was a bit worried. The funny thing is without ACERT my emissions were actually LOWER than last year when I had their muffler! Go figure.