STR posted:

How cold was it outside? Also, it's possible the PO put in a 185 degree thermostat to help keep it cooler in the summer. On some cars (like mine), GM makes pennies and nickles scream in agony when it comes to the radiator; mine will get up to 220ish in normal city traffic if the ac isn't running. Old one with the same engine did the same thing, and a rental Cobalt I had several years ago (also the same engine) did the same according to the DIC.

GM doesn't like to kick on the fans until is happening either. They don't kick on until nearly 220 on my car (old one was the same way), then kick back off around 190 (185 degree thermostat from the factory), unless the AC is running.

If the compressor ever dies, I'm gonna have to figure out a way to turn on the fans manually - the temp gauge gets a bit over 1/2 when they kick on as it is, and I'm pretty sure the old car was in the process of eating its head gasket (mysterious slow coolant loss). I'm sure the ~30 degree temp swings between fan on/fan off didn't help.

It should throw a code for thermostat performance pretty soon if the thermostat is sticking open. I had one stuck half open, which caused it to take a few minutes longer than usual to warm up (which tripped a code), and also caused it to run warm on warmer days that winter.