Overheating issue - I am stumped!

[tucsonjwt]

Step 1 for me would be to get an infrared thermometer and check several places on the engine to see how hot everything really is. I usually shoot it at the thermostat housing to get an idea of the coolant temp. You may just have a bad gauge.

If you have a standard fan clutch it should engage when the engine temp increases to the specified temperature. I have never had any luck with flex fans.

Also, I had the same symptoms on my 2001 Cavalier recently. The temperature would go up to around 230 when idling or on the highway(counter intuitive). I replaced the radiator as suggested by a local mechanic and that seemed to fix the problem.

I would use AC Delco or OEM GM parts whenever possible for the cooling system. Most mechanics around here won't install anything but a ACD of GM fan clutch (they are pricey - maybe $125, but this is not a place for an aftermarket experiment (IMHO.)