HEAD GASKET FAIL
If you recall I have talked to you about R&ring my 1993 6.5L engine for a rebuild or simply replacing it with the ’96/’97 engine that I bought from a guy in Portland. I removed the heads from my original ’93 engine to send to the machine shop to be tested for cracks. We could not see any obvious head gasket failure, but that might not be definitive. The quoted price for a complete rebuild of my cylinder heads is so high that I want to go ahead and install the newer engine in my truck. In looking at the ’96/’97 engine, it does not appear to use the dual thermostat and high-output water pump modification that I have on the ’93 engine, so I want to switch those parts over to the ’96/’97 engine. I also want to install a new timing set and roll in a set of rod and main bearings. What I have been able to determine is that there are differences between the ’96 and ’97 year engines. Is there a way to tell for sure which version that I have? The only casting numbers that I see on the back of the block are 10237141 and J215. I would hate to order the wrong parts. Any suggestion would be very helpful. Cheers, B.J. King Hi B.J., The four-digit J215 date code decodes to July 21, 1995, so it's an engine likely installed in an early 1996 model year vehicle. The seven-digit block casting number of 10237141 also indicates a mid 1990s GM casting—not the best, but also not the worst of the GM castings. If it is crack-free, I'd consider it fit for any duty for which these engines were designed. The GM 6.5L diesel main/rod bearings almost never wear out if the engine was reasonably maintained. I would not mess with the bearings unless there's a good reason to do so. These engines utilized “select-fit” main and rod bearings, meaning there could be slight variations in sizes of bearings to produce the factory-specified clearances. This requires a careful measurement of the rod and main journals and casting bores to know for certain what size bearings to use. I would, however, look for main web cracks in the block. These cracks, if they are present, will emanate from a main cap bolt hole (center 3 mains) and extend upward toward a cylinder—the worst cracks can sometimes reach a water jacket or cause a main web failure.
Look for head cracks in the space between the valves that sometimes appear in the end cylinders of each head. If you can't find any cracks, I'd just clean the cylinder heads, prep the deck surfaces using 80grit wet/dry paper on a flat sanding block, and then reinstall them.
Incidentally, your original 1993 engine's seven-digit casting number should end with the numbers “599.” If yours does, know that that could be the best cylinder block GM produced, because it has the lowest incidence of cracking.