I hang out here on the diesel conversion forum, but now I find my self needing help on a commercial truck and I'm hoping there's someone hanging out here that can help.

There is a 2003 6500 with only 5,400 miles on it at a used equipment yard in town. We have been looking to upgrade our truck for some time and although it is a much nicer truck that we were considering, it appears to be a great deal. It has a CAT engine - but I'm not sure which one, Allison automatic (not sure which one), it is a 26,000 GVW truck, standard cab with a 16' foot dumping flat bed (direct drive hydraulic pump) and 4' stake sides.

It looks brand new. We drove it today and it drives brand new.

My problem is I know nothing about these trucks or about the CAT engine that's in it. I do know a little about the Allison transmission. They are asking $35,000 which from my looking around seems to be a good deal.

Any input would be appreciated.

Peter

 

That year truck will have a 3126B engine, probably 190-210hp. If you PM me the vin I can run it through warranty at work and see if there was any big problems. That combo is tough and will provide you a long service life. TS performance makes a chip for that engine also.

 

Thanks for the reply - Vin is 1GBJ6J1C43F502761.

I did some searching on that engine - it was around a few years and there is some bad press about the late 90's version. Do you know if this is a tier III motor? What its last major revisions was?

Thanks again

Peter

 

The engines from the 90's were 3116 MUI engines. (mechanical unitized injection) The fuel rack bushings liked to wear out and the rivet for the linkage backed out sometimes causing a lot of hassle. It takes specialized equipment to set up the fuel racks and if not done perfectly you will have 1 cylinder overfueling and carrying more load causing a failure. You could usually tell when there was 1 cyl. off, it made a lot of rattle when that hole fired.

The 3126 is a HEUI engine. (hydraulic electronic unitized injection) They use engine oil and pressurize it to work the injectors. They have full electronics and are very reliable. The only somewhat frequent issue I have seen is the injector seals fail putting oil into the fuel. Its pretty easy to find the failed injector. They have a hole on the side of them that they return oil on top of the head and you just see which injector is returning less or none, that is the culprit. I believe you can get a reman injector from CAT for 300$

There is also a allen plug on top of the head that backs out sometimes and the HPOP cannot build enough pressure to fire the injectors. Just pull the valve cover and look on the RH side, about 6" back from the front. It doesnt get gobbled up because the engine shuts off as soon as it comes out.

Occasionally you will also see IAP (injector actuation pressure) sensors fail causing low power. They are less that 100$ and take 5 min to change. To me, these are no big deal and minor compared to other engines. There are really no mechanical issues with them. I have never seen one puke a rod out the side of the block. I have seen melted pistons from people putting gas in them.

 

Thanks for all the great info. So even in 2003 this was an oil pressure actuated injection????

Peter

 

Yes. AS soon as I get to work on Monday I will run the VIN. Like I said, it will provide many years of reliable service. They are not a big powerhouse by any means but they get the job done. You may want to switch the Allison over to transend? You can get it in 5gal buckets at an Allison shop.

If the front seems like it wobbles at 45 or so there is a little trick to that. The kingpin spacer needs tightened up a little. We take 2-3 thousandths off them and retorque. It seems to do the job really well.

A lot of people like to drive around with the park brake set with those trucks. Check the drum mounted on the tail of the tranny and see if its blue. You may be able to use that as negotiating leverage.

If you get it and have any issues, just PM me and I will give you my cell. They are pretty good trucks and only have minor issues, if your truck even has them.

 

I'll agree with that, but the HEUI system is pretty troublesome IMO. We have a bunch of 3126's and C7's in Sterlings and KW's at work. The only problems we have with them are HEUI related. Mine's had the HPOP line blow 4 times, the HPOP pump has died once, the IAP sensor has gone twice, and of course the injector seals have leaked. The truck is an '01 with 168k on it, engine is a 300/860 calibration. The rest of the trucks in the fleet have similar histories. Our clue on when they need injector seals is lots of oil consumption with no puddles. We have one going in for a second round of injector seals this week.

 

OK, So how does this engine compare to the Duramax that replaced it? Should I be looking for one of those instead? Seems like Chevy changed over the next year.

Peter

 

It does seem like when you have the higher HP cals they require more frequent repairs. Most GM's are weak compared to Sterlings and other heavy trucks. Most GM's are like 210/560 or something similar. We were able to put a fire truck cal in a RV one time. IIRC it was 350hp.

IMO the 6.6 Dmax in the 55/6500 is overworked. If you could find one with the 7.8 they are monsters. PPL has them in their line trucks and fully loaded they are very snappy. For a GVWR of 26k the 6.6 is not durable enough for the amount of work it needs to do.

 

Yes, the 7.8 would be the right Durmax. Is that fully eletronic like the 2005 5.9l I have in my 68 Ford? How close are the engines, are the fuel systems similar in design? If I can work in my 5.9l (simple things like injectors) will I be able to work on the 7.8?

Peter

 

almost all of them are factory filled with transynd

 

since when can you get a 6.6 dmax in a 6500?

 

Are you sure? I was almost positive they went exclusively to the cat C7 with the transition to the GMT-560 platform.

ben

 

The 7.8 dmax is fully electronic. High pressure common rail just like the 03+ CTD's. Interestingly its overhead cam as well.

 

From what I could figure out the C7 is an updated version of the 3126. This truck was made just about the time of the change - should be able to figure out which it is from the VIN.

Peter