Expert: Robert Summers - 3/6/2008

Question
Robert, last week my blazer was running warm at stoplights, but the gauge would go down if I changed the heater setting. I took it to a local shop on Thursday for a new thermostat. He replaced the thermostat, but said I needed to bring it back on Monday to fix a manifold intake leak, but I could drive it in the mean time. I had intermittent heat before the leak repair, but now I have no heat at all. The repair guy replaced the thermostat, gaskets and coolant and said he pressure tested the water pump. My vehicle is a 1999 blazer LS x V6 with auto trans.

Answer
Hi Richard... check the heater hoses and see if they both feel hot to the touch when truck at operating temp... if you have one hot and the other not then i would suspect a plugged heater core. coolent is not flowing thru it... if both are not hot then i would suspect that the new thermostat is stuck open not allowing coolent to get hot enough. what was the reason they suspected an intake leak. is the cooling system building too much pressure, or is it burning coolant. if you have compression leaking into cooling system that would also cause no heat as coolant cannot circulate...install cooling system pressure gauge on rad start truck and allow to warm up, it should take some time to build pressure...if it builds fast that could be indaction of compression leak into cooling system...hope this helps