Is a block heater a must-have in extremely cold climates?

Dear Car Talk

Dear Car Talk | Jan 01, 2010

Dear Tom and Ray:

I live in interior Alaska, and it gets cold. How cold, you ask? It's been -40 F (that's negative 40) for the past week or so. My husband and I go back and forth as to whether to keep the car's block heater plugged in all the time, or whether to use a timer and run it only some of the time. I've heard that too much heat is bad for the oil. This morning I used the timer, and my car decided it was too cold for the transmission to engage. I was stuck. At -45 F, I don' t have to go to work. At -40 F, I do (administrative policy). I want to use this as leverage to get my husband to let me keep my car plugged in more of the time. What do you think?

-- Christie

RAY: I'd use the timer, Christie -- a timer that turns the block heater on around Oct. 1 and turns it off around June 30.

TOM: In fact, you may want buy a trailer with a diesel generator bolted onto it, so you can stay plugged in while you drive around, too.

RAY: When it's that cold out, just leave it plugged in all the time if that's what the car needs. The only cost is electricity. You won't do any harm to your oil.

TOM: Right. When people talk about heat being an enemy of motor oil, they're talking about oil that's being overworked under hard driving conditions -- like driving a car at high speeds for long distances in the heat of the summer, or pulling a trailer up the Rockies.

RAY: When you subject your engine to extreme conditions like that, it can run hotter than it's supposed to. That can shorten the life of the oil. That's why manufacturers recommend that people who use their vehicles for such "severe duty" change the oil more frequently.

TOM: But in your block heater's wildest dreams, it never could get the engine oil hot enough to do it any damage. Not even close. In your case, it's just warming it up to the point where it's no longer cement.

RAY: So for weeks like the one you just had, you can run the block heater as much as you need to. And when it gets so cold that the block heater needs its own block heater to get started, it's time to move to San Juan, Puerto Rico, Christie.

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