[ChevLoRay]

I think he's on the same page with us, now. The fact of the matter is that the pump will run, but the stuck mechanical thermostat (like you said) won't let water/coolant circulate. To some folks the whole thing is hard to understand, from a mechanical concept. The way I used to know for sure that a thermostat was stuck, was when one came into the station, steam rolling out from under the hood and usually making a honking sound as the steam passed between the gasket of the radiator cap and the bottom of the radiator filler neck.

If anyone encounters such an event, do NOT take the cap off of the radiator!! Repeat, DO NOT take the cap off of the radiator!! The hot coolant will blow out of the filler neck and you will get burned by it. Get away from the radiator and just be patient. When it has stopped with the honking sound and the steam has dissipated and is no longer blowing, THEN and ONLY THEN can you begin to SAFELY deal with the hot radiator. Start by pouring cool water on top of the radiator cap, doing so for several minutes. When there is no more steam or coolant blowing out, loosen the cap to the first stop. At that time, there may be more coolant that leaks out, but the cap should stay on the radiator. When all of the pressure has stopped venting from the radiator, go ahead and take the cap off. After the engine has cooled down, you can begin the process of replacing the thermostat.