Over Pressure Cooling System

[m38inmaine]

My 86 M1009 snapped the crank a while back so I purchased a 1993 GMC mini bus with a 6.2 showing 92k mies. I drove it down the road a couple of miles and it ran well. So a year later I transplanted the bus engine and now have a question concerning the cooling system. I had the radiator shop clean and repair a small leak in the radiator, new oem thermostat which I tested and works fine . Tried a new cap and one from my current daily driver with same results. Also appears to be a newer water pump. When the engine starts from cold there are large amounts of bubbles and coolant overflowing from the radiator(cap off)and some what appears to be a vapor. Install the cap and it starts forcing bubbles in the overflow tank and all the hoses are super hard . I can only suspect a head gasket is bad but there is no oil in the coolant or coolant in the oil. Also it can sit for a week and when youn take the cap off there is pressure behind it. I would think if a gasket was blown it would leak down. I can't smell any coolant coming from the exhaust either. Any thoughts appreciated.

 

[Keith_J]

Partial failure of the head gasket. There is only a single passage for pressurized oil through the head gaskets, there are 4 big holes with compression pressure that can leak into the cooling passages.

Time to pull the heads and replace gaskets. Also, with a 1992 engine, you should replace the harmonic damper, this is the cause of most crankshaft failures. Look carefully at the rubber ring for ANY splits, cracks or tears and replace if any are found. Rubber gets hard as it ages, this changes the damping qualities negatively.

The damper quells torsional windup of the crank, this is what causes damage. Every time a cylinder comes up on compression, the crank slows. Every time a cylinder fires, the crank speeds up. On a single cylinder engine, this isn't a problem but on multi-cylinder engines, the crank will torsionally vibrate. This causes fatigue of the crank. Diesels are especially vulnerable due to high compression.

 

[southdave]

I did the same with my 1009 same bus motor ect..what I am wandering if the pumbing was different a van verses the 80 D model truck I never look or verified just assume ...

 

[Warthog]

If the van had a serpentine belt, the water pump needs to be changed as the rotation is opposite of the v-belt system. The impeller is different.

It does sound like a bad head gasket.

 

[southdave]

If the van had a serpentine belt, the water pump needs to be changed as the rotation is opposite of the v-belt system. The impeller is different.

It does sound like a bad head gasket.

No but it had some finky bypass off the pump it self and dual thermostate set up on it that swap back cucv style cause of the hoses.. but it too blew the passager head gasket..

 

[MatthewH]

It's a bad head gasket. Had this same issue with my M1009. Turns out it was the pass head, blew out the gasket between the front of the block and the #2 cylinder.

Good Luck

 

[m38inmaine]

It had a regular v belt, sounds like a bad gasket. Thanks, now the work begins.

 

[biggestc69]

I blew a stock radiator. Ordered a new one aluminum with plastic tanks. New thermostat and cap. Drove it for a week same coolant leak. Pressurized it and it was really intermitent. Some it would go a week and then blow coolant everywhere. So I thought the worst, head gasket building pressure on the way out and causing this. Napa has a kit you can buy that will test for hydrocarbons in your anitfreeze. You suck up some of this yellowish fluid in a turkey baster looking deal and with the engine running you suck up some coolant into it and it mixes with the yellow stuff. If it turns a certain color your getting hydrocarbons, head gasket leak, into your system. Turned out I just had two bad radiators back to back. Kit was like 50$ but it saved me from pulling heads. Just something to think about.