even if the thermostat was working properly, it's conceivable that given very low ambient temperatures, enough heat was lost through the heater core to keep the thermostat mostly closed and thus the radiator from doing substantial cooling, since the heater core pulls coolant before it gets to the thermostat and returns it to the water pump inlet.

 

I would agree....especially after only 12 miles.

 

minor thread hijack, but on this note...

cool day, highway driving, fairly level; Where does the needle of the temp gauge typically rest? Mine was very close to the bottom bar. I didn't know if this was typical or if the tstat was sticking open a bit.

(I'm new to these critters, so I'm gonna be asking some odd questions)