6.2 diesel question

[jimmybartz]

I have 83 6.2 chevy diesel in a 1 ton van chassis, since I bought it, it has had a coolant problem, when driving at high speeds 35mph and above it is fine but when you slow down from 35mph to idle it pushes coolant out into the overflow tank, after several times of this happening it will start to overheat from lack of coolant. I have noticed that when slowing down if you downshift the trans. to keep th rpm's high it doesnt do it as bad. when I bought it the guy had just put a new water pump on it, could it be the wrong water pump? I have replaced the thermostat, and radiator cap, it had a 16lb cap and this it what I replaced it with, is this right size cap? The fan clutch looks and feels fine. I have heard of this happening with a cracked head, but if so wouldnt the problem be worse at higher rpm's and higher speeds. And I dont have a compression smell in the radiator. And like I said it doesnt even get hot until the coolant has almost all been pushed out of the radiator, Any ideas you guys might have would be a big help

[84 Convert]

Welcome, Jimmy, you might get more responses if this were posted in the 6.2L forum. I had the same problem with my truck which seems to have bad gaskets, however, I didn't notice a difference based on vehicle speed, probably due to having a manual tranny. I drove it like that for about 20,000 mi. in denial that I had any kind of problem...until the engine hydrolocked itself and wouldn't start. I still haven't gotten the engine opened up, but I doubt that I have a crack into a water passge in the head which is why I suspect the gaskets (both sides).

Good luck and I hope this helps.

Gregg