Keith_J
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Thermostats are proportionally opening devices, they throttle flow of coolant to maintain a certain temperature point. They work on the fact certain types of wax expand when melting, like most solid-liquid pairs act (other than water, ammonia etc). Melting wax forces the valve open via a simple hydraulic system. Over time, some of this hydraulic fluid escapes to the coolant, making the thermostat sluggish. but other times coolant is drawn into the hydraulic portion of the thermostat which causes the valve to open too soon or stay open. Still other times the valve is cocked in the carrier or otherwise impeded in closing.
Just because it passes a single point check doesn't mean it is serviceable. It must close, start to open at the stamped temperature and then fully open at a usually undesignated temperature, at least on the box.
Just because it passes a single point check doesn't mean it is serviceable. It must close, start to open at the stamped temperature and then fully open at a usually undesignated temperature, at least on the box.