Ditch the Thermostat?

by what your saying you may have a clogged radiator then or the thermostat is sticking, never use the NAPA thermostats, I have had 7 of them and none of them the least bit good! the radiator can be unclogged at a rad shop they use a special type of acid under low pressure to unclog them usually works pretty well. If you take the rad out of the car and take it to them (prevents acid accidents with paint) they may not charge very much, last one I got done was 45 at a local shop