1992 Chevy Truck over pressure in cooling system

MARTYNEW

MEMBER
1992 CHEVROLET TRUCK
6 CYL
2WD
MANUAL
296,000 MILES

Recently my truck started getting hot. I've gone through the whole cooling system and replaced everything but the engine i.E. ( Water pump, radiator, termostat, flushed the system ect. )
Yet when I start the truck and let it come up to tempature I've noticed that the raidiator overflow tank starts filling and then starts blowing water out untiil so much water leaves the system that it overheats. Also during this process the raidaitor hose has so much pressure on it it feels like a inflated tire i.E. ( Cannot pinch the hose because there is so much water pressure ). Note I have also checked to make sure there is no water vapor coming from the engine exhaust, there is no oil in the water or water in the oil system. Help Is it possible that the head is cracked somewhere allowing piston compression into the water system? Or a head gasket leak? My next test is going to be a compression test on all cylinders to see if any are lossing compression

3 Replies

PEAR69

MECHANIC
1,482 POSTS

It sounds like your thermostat is sticking closed or is installed backwards. If there is no water in the exhaust then it is unlikely it is a blown head gasket. It is a good idea to do a compression test just to be sure. Which radiator hose has the pressure upper - lower or both? Replace the radiator cap.

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Saturday, November 22nd, 2008 AT 11:30 AM

MARTYNEW

MEMBER
2 POSTS

I have changed the termostat and even gone as far as to remove it completely from the system. The upper raidiator line is the only one I've checked but I will check the lower one as well Thanks for the advice. There will be more information forthcoming as this saga continues Thanks again for the help Marty

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Saturday, November 22nd, 2008 AT 3:26 PM

PEAR69

MECHANIC
1,482 POSTS

It sounds like the water pump is not moving water. Eventhough the pump is new it can still be bad. There should be a plug somewhere in the housing of the water pump. Sometimes the cooling system becomes air bound and you need to remove this plug to vent the system or prime the pump. With the coolant cold, loosen or remove this plug and crank the engine for a very short time and see if coolant squirts out. Then put the plug back in or tighten it and see what happens.
If the water pump is not moving coolant, then the engine will began to boil the coolant and pressure will back up into the radiator and eventually cause your problem. A blocked radiator coil will do the same thing. Keep me posted.

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Saturday, November 22nd, 2008 AT 11:18 PM