Thermostat operation

[inhim]

After the engine heats up and the thermostat is fully open, how big a part dose it have in maintaining engine temp? Does it just stay full open and the temp is maintained by the coolant flow rate and having the right size radiator, or does the opening of the thermostat fluctuate regulating the flow of anti-freeze to maintain the desired engine temp?

[kcg795]

It fluctuates as your driving. Like if you're going up a hill, your engine will create more heat, which will cause the thermostat to open wider. After you've crested over the summit and start going downhill, then your engine won't create as much heat. Then the thermostat can start closing a little bit so that it can maintain normal operating temperature. If you remove your thermostat, chances are that it's going to run very cold or it might run hotter depending on your engine. Engines need that restriction of the thermostat. A fan at the radiator will normally engage if the temperature gets to a certain point above the thermostat opening temperature.

[UncleBob]

actually, most systems, the t-stat fluctuates a lot all the time. For example, the car warms up, and the tstat starts to open, but the coolant its displacing with really cold coolant that was in the radiator, causes the tstat to snap shut.

With an efficient radiator at above crawling speeds, the radiator will be reducing heat too much, and the t-stat will have to constantly move to keep the engine at its preset tstat temp.

This is why you should never see a car get more than 15 degree's over the t-stat temp rating. When you are over the t-stat temp, the fan's come on. If the fans can't overcome the temp, then temp will continue to rise...and then you have overheating. Its a "all or nothing" type situation.