I agree...no matter how much cooling power your radiator and water pump have, no cool water should flow if the therm is working properly. That's why I was so baffled. Like I said, I only changed the rad because this was running very warm on a 180 therm in 40 degree weather, at 55mph. And with Georgia summers, I wasn't going to wait to see what would happen in July! What killed me was that one day it worked just fine, and the next it wouldn't warm up at all! Oye! Going to go to another shop tomorrow and try a different brand just to see. But this is just one of those really wierd gremlins that we get occasionally...and it drives us nuts! Thanks again for all the advice so far...I'll let you know what shows up and what I find out.