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Thermostats

By Neal Kwort, MACS Technical Correspondent

 

As you know, engines have to be warm to run efficiently for drivability, emissions and fuel economy. But why is this necessary? It’s got to do with the volatility (the capability of fuel to evaporate) of gasoline. Liquid gasoline won’t burn. It has to be in vapor form. If not in vapor form, the gasoline simply exits the engine the same way it came in: as potential energy. Without combustion, potential energy doesn’t get converted to heat energy. That means it doesn’t contribute to power. This compromises drivability, raises emissions and lowers fuel economy. So, when atomized gasoline is running through cold engine components, fuel drops out and is wasted. Modern engines are less susceptible to these issues, because fuel is injected at the intake ports or directly into the combustion chambers, but they still exist to a lesser degree.

The thermostat is the component that allows the engine to warm-up. You may have heard that the thermostat regulates engine temperature. That’s actually not true. What the thermostat does is keep the engine at a minimum temperature. What regulates the temperature is a combination of the thermostat on the low side and the cooling fan on the high side. The cooling fan is the device that keeps the engine from getting too hot. The thermostat begins to open and allow coolant to flow at a minimum temperature, typically 195°F. If working properly, once the coolant reaches that temperature, it won’t drop below it. Yet the thermostat does nothing to keep the coolant from going above 195°F. In fact, nothing in the cooling system does. But if the coolant temperature reaches its high threshold, the cooling fan comes on, typically at 225°F. (Read more)

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