Hi, I have a '95 chev silverado 4x4 - I've replaced the radiator (it ran hot, overheated, and leaked) I replaced the thermostat and the heater core twice (it keeps blowing out). I've never had good heat from the heater in the truck and I can sometimes hear the water gurgle back into the overflow jug when I shut the truck off. As I said, the heater core blew out again. Could a bad water pump cause a heater core to blow out? That would explain the no heat issue. Any advice? Thanks.
madness
Sounds more like you have a head gasket leak. I would run a pressure test on it or run a combustion gas test on it.
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There is and adjustment for the heat flap just behind the dash, and about 1 foot left of the glove box. Make sure the cable is adjusted as far apart as you can. This will make sure that the flap that controls airflow over the heater core is fully closed. You also need to have the proper radiator cap. Yours sounds like its keeping too much pressure in the system. After you get the right cap, you will need to check the level each day for about a week. It will take more water over that time as it works out the air pockets. With the right cap, you should be fine. In case you cant find the heater core flap adjustment where I said it should be, just follow the cable from the ac/heater control box (The massive black thing your core is in) to a place where you can make an adjustment. It might be behind the controls also.
Hope that helps.
HDS
I would second that answer. Not a truck, but a 1990 Pontiac started losing antifreeze, radiator leaks in several places. My mechanic pressure tested the system and said the system should show maybe 15 psi max when the engine was completely up to operation temperature. What happened was after only 3-4 minutes from a cold start it would show 20 psi. It turned out to be pinhole leak in the head gasket allowing compression to leak into the cooling system.
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