1998 STS Overheating and blows cold air. HELP!
 

I have a 98 STS 65,000 miles on it. It is overheating and only blows cool air. Well I should say sometimes it blows hot air. If your going up hill the temp will change will to whatever its not doing. If its cold, you go up hill...its now hot. You dig? I have changed the thermostat....3 times. I have changed the water pump. I have changed the radiator cap. I'm at my wits end. I was told it may be the head gasket...anyone have any other ideas? My father thinks maybe the heater core. Oh I should add that there is no coolant in the oil however it is burning through coolant and you can smell coolant coming from the engine compartment when the engine it hot. Please help...

If cooling system is low you will get intermittent or little heat. Since you smell coolant - pressure test cooling system check for external leak. If no leak is found have CO test done to check for blown head gasket. How high does engine temp get to?

It will flash the engine overheat shutting down turn off A/C message...it gets HOT

Hi, Love your boat picture. My 1998 Cadillac has past all the tests, head gasket, compression test. Came out fine. If the car had a head gasket problem wouldn't the car be running rough? The car runs smooth as ever!! Reading other problems could it be someplace where I can't see like; like the coolant bypass pipes near fire wall?

wont necessarily run rough or smoke in beginning. Overheating at highway speeds is most consistent condition. Heater pipes can rust thru causing low coolant level leading to head gasket failure. What has been done or tested so far?

Change your expansion tank, check all fittings of coolant hoses and quick connecters you disassembled for possible leaks. Leaks at times only show up under pressure. Also have a look at the rear heater hose tube that runs at bottom of oil pan closer to the catalytic converter. Those pipes tend to rust and leak. Also add the sealant pellets from AC Delco, it needs them and should not be forgotten.