Okay, thanks for the explaination. I was watching for a drop in coolant level, but never really noticed one- it may have just been more subtle than I was expecting.

I did notice my temperature drop dramatically after about 15 minutes, then rise back to normal after a few more minutes. Does this mean I need a new thermostat?

Probably not. The drop was probably when the thermostat opened for the first time. If the temperature then stayed at the normal reading the thermostat is probably OK.

BTW, nearly all thermostats when they fail will stay closed, causing a boil over. There are new thermostats on the market that if they fail they will open and stay open preventing overheating. A drop in coolant level indicates that there was air trapped in the system somewhere and when the thermostat opened and circulated the coolant the air escaped through the radiator cap. Simply add a little more coolant and re-check it after a short drive.

2ManyZs:

Great thermostat operation explanation!

As I read the post, it was like lights coming on. I thought, "Of course. That's how it has to work. I know that. So why is it like new informarion?" I'm sure if someone had asked me the question I would have just answered, "It's open or closed" without even thinking about it. Most of us don't naturally think thermodynamically and, until we have a problem, we also probably don't think about how the thermostat functions.

If I may make a suggestion - why don't you put it in the Technical Articles section? It's too good to lose. (Mike - if Keith is too modest, please do it for him.)

JIM DOZIER