Hey everyone, I'm knew to diesels and been considering getting own for work. I travel a bit since i'm a welder by trade. My question is how are the 1995-2000 6.5L trucks as far as MPG and reliability? I've seen a couple 3/4 ton 4x4's for sale but don't know much about diesels. I seen in here where someone said to stay away from the 97 and up 6.5L because of the lower end. Any help is appreciated. Thanks, Jason
Well, the oil spray blocks (so-called because they have piston oil squirters in the main bulkheads) do have a higher chance of main bulkhead failures vs the earlier blocks. Those would be late 96-2000 vintage blocks. These blocks also had higher odds of suffering the #8 cylinder cracking problem. Late 2001 and up 6.5's are made by AM General using blocks cast by International. These blocks have the cracking issues fixed; so do the heads. Many of the problem engines have been replaced with AMG under warranty, but there are still many more out there. The only way to tell is to look for the tell-tale International diamond casting symbol in the block valley. It will probably be very difficult to see with the IP in place. Here is a pic of an AMG engine:
The numbers 1-7, as indicated in the above photo help to describe how to identify these blocks.
1- The Navistar symbol is cast into the engine valley.
2- The "506" casting number can be found in a few places on the block. The two #2's as identifed on the photo include the 506 number.
3- The casting date is also an indicator of when the block was actually cast by International. It should show a date of November 2001 or newer.
4- These blocks include two Oil Pressure Switch ports. The valley location was used by the 1996 or newer civilian model engines.
5- The OPS bellhousing flange location was used by the 1992-95 civilian model engines.
6- This pipe is used as a valley drain. Any liquid accumulating in the valley can drain through this line to a location above the oil filter.
7- This is the engine speed sensor used by the 4L80-E automatic. It is afixed atop the oil pump drive assembly.
Now, if it isn't an AMG engine that doesn't mean it's bad. However, it is possible the block could have cracks in the main webs; the only way to tell is to drop the pan and closely inspect the main bulkheads. Basically, the 97-2000 GM blocks are the 6.5 version of the dreaded "53" Cummins blocks. They might last awhile, or they might crack and fail. If the block is crack-free you can greatly reduce the odds of a crack starting by installing main studs and a girdle. The oil sprayers are another stress point that the earlier blocks don't have, but IIRC most cracks start in the same place on these blocks as on the earlier blocks - the sprayers just speed the failure along.
I should point out that block cracking was a potential issue in ALL 6.2's and 6.5's. I have studied the issue, and I am convinced that the cause is due to GM using a counterbore too deep and bolts too short in the outer main holes. The bolts only engage about 3/8" of thread in the blocks I have seen, and FEA has shown that the stress concentration there is HUGE. That is why cracks start there, rather than at the much more highly loaded inner bolt holes. I believe that by simply replacing the bolts with studs long enough to engage the entire length of thread in these holes that these failures won't occur. A girdle is an extra measure of protection. I have not heard of anyone having a known crack-free block fail when this is done. Personally, if I were to buy a 6.2/6.5 powered vehicle I would drop the pan and install a girdle after checking the main webs. If the mains are cracked I would plan on getting a new motor soon.
Also, watch out for a failing harmonic damper. If it fails, then the crank is likely to break. If you buy a 6.2 or 6.5 replace the damper whether it looks like it needs it or not, because it probably hasn't ever been replaced.
The other big 6.5 issue is on 94-up engines. These engines use the Stanadyne DS-4 electronically-controlled IP. To many these are well known for having IP failures, but in reality the DS-4 is a long-lived, trouble-free pump. The problem is the PMD/FSD (Pump Mounted Driver or Fuel Solenoid Driver - two different names for the same thing). It is mounted on the side of the pump and generates a lot of heat - and the pump, which is attached to a hot engine, is the heat sink. Eventually this module fails, and the ignorant service techs end up replacing the whole pump (big $$$
). Many vendors sell kits to remotely mount the PMD on a n external heat sink, and this generally ends the failure issues. 92-93 6.5's, and of course all 6.2's use the mechainical Stanadyne DB-2 which are very reliable, trouble-free pumps (the early ones had a plastic ring in them that would fail, but these have pretty much all been replaced by now).
As far as mileage goes, the 6.5TD's are pretty good - they are definitely much better than a gasser. The earlier 6.2's tend to be better, but they don't have near the power.
Hopefully I haven't scared you away from this engine family. They do have their potential issues, but they are all fixable. The trick is knowing whether your potential purchase is crack-free before you buy. Short of dropping the pan there is really no way to know. As a rule, 96 and earlier have a better chance of being crack free, but there are no guarantees. In any case, get a stud girdle kit and put it on. If these problems are prevented these motors are actually pretty trouble free and tend to last a long time.
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