Frank believes that the heater setting has nothing to do with engine warm up. Is he right?

Dear Car Talk

Dear Car Talk | Oct 01, 1992

Dear Tom and Ray:

After long hours studying the service manuals of several brands of cars, I have concluded that you may be wrong about thermostats, car warm up, and coolant flow. A car's thermostat keeps the coolant circulating in the engine until it warms to a certain temperature. At that point, the coolant is allowed to flow into the other portions of the system (like the heater). You said the heater control should be left "off" until the car warms up. I believe the heater setting has nothing to do with engine warm up. Am I wrong?

TOM: Yup.

RAY: First of all Frank, let's be clear about what we said. We said that if you want to be picky, it's theoretically better for the engine if you leave the heat off until the engine warms up. It may not be best for your tootsies when your toes are frozen together, but it IS best for the engine.

TOM: And the heater setting DOES affect engine temperature. The thermostat prevents the flow of coolant to the radiator only. It doesn't stop the coolant from flowing to the heater core when the engine is cold.

RAY: And since the heater core is basically a small radiator, it dissipates heat and takes heat away from the engine.

TOM: So if you want to warm up your engine as quickly as possible, leave the heat off. But if you want to unfreeze your toes as quickly as possible, do what everybody else does and put the fan on "high" at the first sign of lukewarm air.

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