I have one in a 1999 C3500HD. I like the motor personally, its relativley cheap to work on. The one I have wasn't abused at all prior to my purchasing it, and also since I've had it, it's been well taken care of. However, a few problems I've had and they seem to be common:
1. Stalling issues, the PMD which is the pump mount driver, is known to overheat and cause hard starting/stalling issues. There is a simple fix for this that involves using an extension cable and a new PMD and moving it outside the engine bay.
2. Lift pumps, I've replaced two of mine in my truck. However, the original ones had 200,000 miles on them.
3. The truck developed a "thumping" out of the blue one day, coming straight out of the intake, and also low power. Not a huge drop but enough to notice. The thumping didn't get worse, however the turbo also started puking oil at the same time. Come to find out, these trucks are known to collapse lifters, and mine did, on the exhaust valve, and the "thumping" was actually air being pushed back out the intake because it could not escape out the exhaust valve. This job was not a simple day job, since the heads must be removed to replace all the lifters. The turbo also was junk because all the air being pushed out the turbo also pushed the oil out with it, causing the turbine bearings to wear. However, the entire job cost me about a grand which isn't to bad considering I replaced the glow plugs, head gaskets, intake gaskets, 16 lifters, and other misc. things such as anti freeze and oil.
4. Injectors are known to spray streams of fuel burning holes into the top of the pistons.
All in all though, my truck has 210,000 on it now, and it has been a great truck with decent power. It needs to be taken care of and doesn't like to be abused, and also doesn't like huge power upgrades. I'm real familier with these diesels so any questions you have please feel free to ask!
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