M11 vs c-12

IMHO the C12 will out last & out pull an M11. The M11 might do better on fuel. I've driven a couple of C12's with 800K+ & no overhaul, I think they're good hearted little motors. Stay away from the C13's, total garbage.

 

What is the hp/tq rating on each motor, that would be the deciding figure for me, they are both good engines for light loads, the M-11 will get better fuel mileage and is a much less expensive motor for parts.

 

The M11 is a solid motor with good fuel economy. The C12 loves to use oil and burn a lot of fuel. My advice, get the M11. The C12 has a lot of power, very strong jakes and sounds pretty good, but the longevity is not there. When I worked at Ryder, they tended to grenade themselves.

 

I own the child of the M11...the ISM. I get 6.5mpg and she has 425 horses. Parts are cheap and plentiful. Do a few things before you buy the M11. See a hot oil pressure over 20lbs idle and hot I mean 180 plus........stick your finger in the blow by tube , find no oil and see no vapor at idle and then get a flashlight, look at the back of the block where the head mates up, see no oil at all there. If the head gasket is leaking oil its going south and it won't be long either.

Good hunting

 

I have an M11 in a 1998 T800. 13OD, 4.33 rear, 22.5" lo pro rubber. 1750 RPM at 62 mph. I've driven the truck since 2007 and it has 1.2 million miles on the chassis. I have always pulled 80,000 SB on I-81 through NY and PA. NB I am grossing 30,000 - 50,000.


It blew a head gasket straight away. KW dealer put a new head gasket in there and planed the head. That lasted a couple of months and then it blew another head gasket. Dealer took the blame because they didn't use new head bolts. We had to buy a new head this time. Throw in rods and mains and a new turbo that was bad from the git go and we dropped $13,000 in the first 12 months.

Less than a year later it blows a third head gasket when I was climbing Mt Pocono grossing ~85,000. She hydro locked. This time I avoid the KW dealer and take it to an old timer. He said why don't we fix the problem instead of putting another head gasket like those stupid kids that work at the dealership. So he measured liner protrusion and found that one was sunk. We decided to replace pistons, liners, rods, mains. The rebuild kit cost $3,025 (no head, no injectors). He charged 40 hrs labor. She now has 185,000 miles on that rebuild.

I get 6.5 to 7.5 miles per US gallon which is at least a full mpg better that next best truck in our 4 truck fleet (2001 6Nz Cat, 2005 Acert Cat, 2008 ISX). Based on 100,000 miles/yr, I think that works out to a fuel saving of at least $13,000/yr. 1.5 mpg saving would be $20,000.

She does leak oil. It leaks from the oil pan gasket. It leaks from the back of the head. It leaks from the accessory drive cover. It leaks from the bottom AC compressor mount bolt.

I would buy another. Only problem I see is she maybe needs more rear gear than a big bore engine, which makes it rev higher.

 

If combine the c-12 with 13 sp, you'll have power and good mpg. The c-12 you refer, you probably talking about the one was built along with mbn c-15.

 

The later C-12's were the best 2001-2003, the reason I asked what hp rating you were looking at is because there are a LOT of rental truck chassis out there with M11's rated at 280-350 hp stay away from them, you want to be in the 370-425 range.