Should I warm up the car with the heat and fan on or off?

Dear Car Talk

Dear Car Talk | Sep 01, 2000

Dear Tom and Ray:

I live in Portland, Maine (cold winters), and I own a 2000 Nissan Pathfinder. My husband told me that on winter mornings, I should leave the temperature knob all the way to the "cold" position until my engine heats up. He says this will allow my engine to warm up properly and will be better for my engine. I want to leave the temperature knob all the way on "hot" with the fan off. Then once I start feeling some heat seeping in, I'll turn on the fan. He tells me that this will reduce the life of my engine, and that if I keep doing it, I'll start experiencing problems. Is he right? -- Carrie

RAY: This is the kind of thing that men spend hours and hours contemplating, Carrie.

TOM: Hours? Years! I mean, there's probably not a man alive who hasn't wondered about the proper position of the heat knob while the car is warming up.

RAY: And because your husband has given so much thought to this, it would be a severe blow to his ego if you were to prove him wrong, Carrie. He might never recover from it.

TOM: So we're not going to print here that it makes no difference what you do with the temperature knob.

RAY: Right. We'll explain that to you in a private little note we're going to send later.

TOM: Let's just say, in print, for the record, that your husband is technically correct. Because the heat exchanger under the dashboard is just like another radiator, it does take some heat away from the engine. So leaving the temperature knob in the "hot" position will cause the engine to take a little longer to warm up. How much longer? A few seconds? A minute? I don't know.

RAY: But as we'll explain in our private letter to you later, Carrie, it's so insignificant that it won't make any meaningful difference in the life or reliability of the engine. So for practical purposes, you can do whatever you want and not worry about it.

TOM: Moreover, what's more important? The life of the engine or the temperature of your fingers? Let's get serious here, right, Carrie?

RAY: So now you face the classic marital dilemma: Would you rather be right, or would you rather be happy?

TOM: Well, believe it or not, we have a solution that allows you to be both. Invest in a block heater. For people who live in the great frozen tundra like you guys, an electric block heater is a wonderful thing. You plug it into a timer, so it heats up your coolant a couple of hours before you start the car in the morning. And then you have instant heat and instant engine operating temperature.

RAY: That keeps your fingers warm, your engine warm and the home fires burning, if you know what I mean. Sounds like the perfect anniversary gift to me. In fact, isn't the 10th anniversary the block-heater anniversary?

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