is the temp guage staying low or going up to the hot mark? if the temp needle is staying low, the car is taking forever to warm up and u r not getting much heat then id say its the thermostat. it can be sticking mostly open. it the temp needle is in the hot range then its stuck shut and u will over heat. if the needle is bouncying around and not much heat then its stuck open. i wouldnt bother with the stove thing. thermostats r cheap and easy to replace it would be a waste of time to check it.