Is it better to wait for the engine to warm up before turning on the heat?

Dear Car Talk

Dear Car Talk | Jan 01, 2002

Dear Tom and Ray:

It gets a bit cold in the winter in Fairbanks, Alaska, and I have had an ongoing dispute with several wives and girlfriends about an important issue. When a car has sat outside all night and one starts it in the morning, I contend that one should keep the heater turned totally off until the temperature gauge moves, and then turn it on. My female compatriots, on the other hand, always wanted to turn the heater up high, with the fan blasting, even when the air pouring out was frigid. My theory is that by turning off the heater, you reduce the size of the circuit through which the coolant has to flow. Thus, it should warm up faster. Am I right? -- John

TOM: John, pay attention. I'm going to ask you a question that might save you from having even more ex-wives: Would you rather be right, or would you rather be happy?

RAY: My brother figured that out sometime in his fourth decade. And then again in his fifth, and again in his sixth.

TOM: As to your mechanical question, you are technically correct. The heat exchanger under your dashboard is a little radiator. So when you have the heat on, you are removing heat from the engine and are transferring it to the passenger compartment. So if your goal is to get the engine to warm up as quickly as possible, you want to keep that "passenger compartment radiator" off until the engine is warm.

RAY: Does it matter to the engine? Hardly. But technically, you are correct.

TOM: The womenfolk, on the other hand, couldn't give two bits about the engine. They're interested in comfort. And if you want to be happy, John, you should get interested in comfort, too. And for maximum comfort, here's the procedure we recommend.

RAY: First, don't turn on the fan right away. That's just dumb, and your exes are all wrong about that. It results in an arctic mass of Canadian air blowing up your pant leg -- and no one finds that comfortable. Using the fan while the engine is cold does nothing to warm up the engine faster. In fact, it slows down the process.

TOM: So make sure the fan is off. Then, after you start the car, turn the heat lever all the way to hot (or from blue to red). That way, as soon as an inkling of heat is available, it will begin to seep into the passenger compartment. But with the fan off, you won't get that awful northern gale while you wait.

RAY: How long it takes to get heat varies from engine to engine and from day to day. But as a general rule, once the temperature needle moves at all -- as soon as it moves from the bottom of the "C" to the top of the "C" -- then you're cleared to turn on the fan. That generally happens in three to five minutes. And if, for some reason, you don't have decent heat by then, turn the fan back off and try again in a minute or two.

TOM: And before you say "But! But! But! ..." go back and read the first paragraph again, John.

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