my car likes to overheat but mainly when its hot out side. i have a 94 ls.. and sometimes when it gets to hot i hear hissing sounds from under the hood and the coolant resevoir over floods.. how can i diagnose this problem someone help me... i dont think its the thermostat because it would over heat all the time and not only when its hot out...

 

replace your radiator cap first. I just went thru hell with cooling problems. The thermostat is not at all hard to replace so i would do that just to be sure.

 

Could be a couple of things but it sounds like a blown headgasket.

 

I think it is the thermostat, not letting the coolant flow. I'm assuming you are keeping it full...yes? Does the engine temp go down when you turn the heater on full blast?

Headgasket? WTF? He's not burning up coolant, it's boiling out.

 

99% chance you blew a head gasket it is the ONLY reason I know of that would cause cooland to bubble out of the overflow tank as soon as the car was started or shortly there after. If you have a non functional fan the car would overheat at low speeds and be fine at highway speeds

 

Well, the headgasket being blown can cause you to pressurize the system and you would get air flowing through causing coolant to displace to the overflow tank. My car did this. Check to see if when you turn the radiator cap you hear air bubbling in the overflow tank. If it does, it is the gasket.

 

Huh, new one for me. Wouldn't he also be losing coolant? White exhaust smoke? Coolant smell to it?

 

well i did a check on the car today and i have a few questions. when you unscrew the radiator cap am i supposse to hear the radiator getting depressurized? like a hissing sound? i changed my radiator cap and with the old one i didnt hear the radiator getting depressurized but with the new one i do. i also changed the thermoswitch just to be on the safe side and now my car is running normal again and the fans come on when they're suppossed to... thanks for your help guys.. i definitely knew it wasnt my headgasket because of no mixture of oil in the resevoir or smoke coming out of the exhaust... but thanks again guys..

 

It could be that the fan switch sensor is slow in turning on. I had this problem recently after lapping at the track. The fan won't come on until few minutes later when the Defi water temp already hits 120 degrees C (max), but the funny thing was that the factory water temp is slightly pass the halfway mark. For my temporary solution, I had the fan switch shorted out so that it is constantly on. The overheating is gone. The next thing I need to do is to get a Spoon thermoswitch to switch the fan on at a lower temp.