Quote Originally Posted by mbeige View Post
What temperature does the thermoswitch open? It should be indicated/etched on the side or something. That way you know what to expect when the coolant temp reaches that temp (fans should start).

Agree on replacing thermostat. Get one that's set lower than factory. If it says it opens at a certain temperature, it means it just starts to open at that temperature, but the operating temperature of the car will be higher since the thermostat is only rated to open at that temp. It will be fully open a few degrees higher.
removal and checking the thermostat is fairly easy.
1. remove the upper radiator hose
2. unscrew the two or three bolts of the thermostat housing, noting the gasket and / or mounting position.
3. visually inspect the thermostat for corrosion (rust), cracked or broken coil. perform a test on the thermostat.you'll need to submerge the thermostat fully in a pot. have a thermometer ready to take the temp. reading.
4. bring water to desired temperature (i.e. thermostat working temperature etched on its top) and observe if the thermostat opens. take note at what temperature it opened then compare it to specs. replace, if it opened way too late or too far up the thermometer or if it didn't open at all.
5. re - install the new or re-conditioned thermostat, housing, bolts and hoses.

i recommend against replacing the original thermostat (oem) with a lower rating. the thermostat is designed to open at a certain water/coolant temperature. this condition happens when the engine has achieved its operating temperature. the job of the thermostat is to allow the engine to warm up quickly (for optimum performance) during start up and maintain its operating temperature by opening (if it gets too hot) and closing (if it falls below operating temp.) this has been pre-determined by OEM and pretty much established by the car manufacturer's specs.
the idea of having a low rated thermostat is to let the engine operate at a slightly cooler operating temperature since heat (summer season) definitely affects engine temp. via radiative/convective/conductive heating.
however, to offset this dilemma, you can perform a lot of adjunctive means to avoid overheating other than picking on the thermostat (unless it needs replacement) : the main thing is regular maintenance (engine flushing and radiator flushing recommended), strict compliance with coolant application, regular oil change and tune up, etc..
modifying the engine bay helps. does your hood already have thermal insulation (you know that aluminum or aluminized sheath with polymeric padding- white) underneath it?insulating the cowl and the firewall helps as well.