: My 99 STS Overheated

02-17-04, 06:30 PM
I left work, drove about amile on the freeway looked down and saw the temperature start rising, went to red in like 30 seconds, pulled over, said engine hot turn ac off. Turned car off, popped the hood and a ton of smoke came out. It has 74K miles on it, i put 20k on it since i bought it last January. Since I bought it I felt like something was up with it. The temp was always dancing around the middle line. Had it pressure tested by GM and told them what was going on, they said it was all normal. I smelt coolant, they said it probably just the stuff the dealer used to clean the engine with. Said it was running hot, told me that is how they run. Finally I developed a coolant leak, took it to a shop, had the water pump changed. Had no more leak but my coolant was still disappearing and I was still adding coolant once a week. Now this, hopefully its not a head gasket, going to get it checked this week. Any ideas what it might be? Since I'e owned it, all I have done is oil changes every 3k, had the brakes changes, the water pump changed, and added things to the appearance and entertainment system. I know you guys can just guess, but it might make me feel better... thanks

02-17-04, 08:20 PM
first of all is your coolant level still dropping rapidly???
if not it could possibly be your radiator is plugged and the fluid is not circulating.

02-17-04, 09:13 PM
It was dropping rapidly before it happened, added some once a week

02-17-04, 10:33 PM
Well...if the coolant was disappearing it had to go somewhere.... no obvious leaks or coolant anywhere??
Did the system just get so low it overheated and the engine is OK now that it is refilled....???..just the coolant loss is still the problem?

The head gasket is the most obvious conclusion to jump to...but there are several good checks that can be done to ascertain if it is the head gasket causing the coolant loss or something else.

You can pressurize the cooling system with a coolant system pressure pump. Look for obvious leaks and such. Leave the full system pressurized for several hours even if you have to pump it back up occasionally. Pull the spark plugs while you have the system pressurized and waiting. After several hours of having pressure on the full system crank the engine over with the plugs out and see if any coolant blows out any of the spark plug ports. Sure sign of head gasket...or sure sign that it is OK if nothing comes out.

Or...you can pressurize each of the cylinders with shop air thru the spark plug port. Just hook the air up to the spark plug port with the cooling sytem full and take the cap off the pressurized surge tank. Watch the cooling system for bubbling when you pressurize each cylinder. Sure sign of head gasket failure if it bubbles...or sure sign that it is OK if not.

Drain the cooling system and pressurize it empty with the tester pump. Listen at each spark plug port for hissing or the sound of an air leak. Sometimes if the leak is really small the coolant will not leak thru or leak thru so slowly that it is almost undetectable...but air will leak much easier and pinpoint the leak source.

Or, you could try refilling the sytem with fresh 50/50 DexCool/distilled water, dose the system with the cooling system sealer that is suppose to be in the system anyway and see what happens. Maybe there is a small leak in the valley of the engine that is harmless but causes the coolant loss. The sealant will stop that sort of leak and coolant loss. Use the GM coolant supplement pellets(6) or two tubes of the BarsLeaks "golden seal" powder. Install it in the radiator hose NOT in the pressurized surge tank for it to be effective.

02-18-04, 05:24 PM
Thanks, so if it is not headgasket trouble and I pulled over as soon as it started to over heat, just about at the red line when I stopped but there was a lot of smoke, could the engine still be okay or is it pretty likely that i f***ed it up when it overheated??

02-18-04, 06:03 PM
They are well designed. Even the ones that overheated seem to be OK when the cause is fixed.