Expert: Robert Summers - 12/10/2007

Question
i have a 1990 chevy k1500 v8 5.7 liter and has a coolant problem it will rise to the red area and jump way down and rise again and some time have to shut truck off and let it cool down for a couple mins.. replaced the thermostat and still does it.. and the coolant will over flow when cap is off and then go back down. might it be a head gasket?

Answer
Hi Travis... That would be my first guess... put on a pressure gauge and watch to see how fast pressure rises... if you come to pressure right away you have a compression leak into the cooling system. if not then check the system for obstructions and or poor flow from the pump...hope this helps...merry christmas