i have a 99 blazer with 4.3l and 4wd. two days ago it started overheating on me. about 1 ago (8,000 miles) i replaced both the water pump and the thermostat. there were no puddles on the ground so i don't think there are any leaks. i took it to a shop and they flushed the radiator. they said the cooling system was super dirty so they put a cleaner in it and then flushed it twice. they pressure checked it and found no leaks. it still overheated after that. i replaced the thermostat again and it still overheats. it doesn't look like the thermostat is opening according to the guage in the dash. also the heater does not seem to get hot. any ideas on what else could be wrong??? please help!! thanks.

 

Are you loosing any coolant? Check your coolant level everyday first thing in the morning before doing any driving. If you are loosing some coolant, you may have a bad intake manifold gasket, YES even though the shop tested it and found no leaks.

My '96 was overheating, loosing coolant, first very slowly, then quite quickly, and my heater wasn't blowing any warm air. The ultimate problem was a blown intake manifold gasket. You can't always tell if coolant is leaking into the oil, especially if it's happening slowly, but all your symptoms point to the gaskets, IMHO.

 

just double checking. is the spring supposed to be up or down on the thermostat? i just want to make sure i didn't put it in backwards!

 

Down.