1984 GMC 6.2L diesel overheating. HELP!
 

The truck in the subject line has been having overheating problems. It seems to drink coolant. No coolant leak can be found. The thermostat checks out ok. I am changing all of the drive belts today on the off chance that one of them loose and impairing pump function. I have always had a suspicion that the coolant return system was failing. But I really don't know how to diagnose that beyond checking the tube for leaks. There is a possiblity that the EGR is screwy but I had the impression that it failing is a pretty rare thing. I don't have a code checker. Any advice about this beast would be appreciated. :crazy:

with the engine running and the radiator cap off, look at the coolant and if you see a lot of bubbles, it could be exhaust leaking into the coolant=bad head gasket. You can also pressure test the cooling system as well as the radiator cap to see if either of those are leaking. Check at your local auto parts store, some will perform this kind of test for free.

Take it into a dealer and they can run a test to see if your burning it or have any leaks....the test is fairly cheap and is pretty accurate.

Thanks for the tips guys. I was beginning to think either head gasket or some sort of weird EGR malfunction. Nothing else seems wrong that could account for the temperature spikes I'm seeing.

Probably the head gasket. I have an 82 gmc 6.2 and the older versions of that engine seem to be prone to blowing head gaskets. It happened twice on my original engine and then again on one I got fro a wrecked truck.

if the coolant is disappearing but there is not external leak, then the ONLY possibility is an internal leak. 99.9999% of the time it is a head gasket.

by the way, the EGR (exhaust gas recirculation) valve has nothing to do with engine coolant.

check your oil pan to see if its got coolant mixed in.

If it's the head gasket you should see smoke coming out of the tailpipe when it starts. Not the usual black smoke but blue or white smoke.

I agree though, it's got to be either the head gasket or a cracked block.

Either way, better get a second mortgage on the house to pay for it. LOTS of money in these parts.

nah, not really that expensive. I just checked www.partsamerica.com, and they list a head gasket for that truck at about $35. now granted, prices vary from place to place (im in central Ohio) but whereever zampolit is the price shouldnt be more than $50 for a single head gasket. IF (and I should stress IF) that is all that is wrong is just one blown head gasket, then I would think you could get it replaced by a reputable mechanic for $150-$200, parts and labor.

However, you may want to consider getting both heads done, meaning removal of both heads, and a complete valve job done on them while they are off. That is, if a) the truck is still in decent enough shape to warrant putting the extra cash into and b) you plan on keeping it for a while longer (like 2+ years). Of course, this extra work will cost you quite a bit more (probably in the neighborhood of $800-$1000 for everything. but compared to buying a new truck, thats pocket change.