[samckitt]

The part of the thermostat that reacts to the temperature is on the back side of the "valve" away from the cooler fluid. The engine side is hotter & opens up to allow cool fluid through, it closes if temperature drops, recirculating warmer fluid from the engine back through it. I would say you have a bad thermostat, but you say you are on the 3rd or 4th one. So i'm confused too.