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How cold should it be before I plug my car into a block heater?

We have a new car parked outdoors for the winter and I am not sure how often I need to plug in the block heater. We live in Winnipeg where temperatures dip below -30C and I only use the car once or twice a week. What is best for the car to ensure it starts every time? — Kara, Winnipeg

Cold weather grates on most of us, your car included. A modern car should start when it's -30C if it hasn't been plugged in, but it won't like it.

"People call and say 'my car starts at -20 or -30 or -40,' but it's in your car's best interest to plug it in before you use it when it's around -15C," says Liz Kulyk, communications manager for CAA Manitoba. "It's for the longevity of the car — to make sure the engine components are getting enough oil and reduce wear."

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Block Heaters 101

When the engine starts, it pumps oil through the engine block to lubricate moving parts. When the temperature drops, the oil is thick and doesn't flow like it should.

Less oil flow means more friction — and that means engine parts wear faster than they should. A block heater warms the engine coolant, which warms the engine block and the oil.

Plugging in your car before you start it can also lower your car's emissions — and your gasoline bill, says Natural Resources Canada. At -20C, a block heater can improve your fuel economy by as much as 10 per cent, the NRC says.

Canadian idle?

In the winter, a cold engine burns more gas and produces more tailpipe emissions. That's why idling for 10 or 15 minutes to warm up your car isn't such a hot idea — you're polluting and burning more gas than you would be if you were driving. It's better to just get in and drive until the car reaches it's proper operating temperature, NRC says.

A block heater can give you a head start by warming up the engine.

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The heater doesn't heat your car's interior. But, the warmer your engine is, the better it will heat the air that will blow into the vehicle and keep you from freezing to death, Kulyk says.

"When it's been plugged in, the vehicle will warm up in 5 to 6 minutes instead of 10," Kulyk says.

When to plug it in

NRC says to plug in a car two hours before you drive. But CAA Manitoba says your car needs to be plugged in for 3-4 hours, especially when it's colder.

"Two hours isn't long enough when it's -30C," says Kulyk.

A 1972 University of Saskatchewan study found that a block heater will get an engine about as warm as it will ever get after about four hours. After that, the extra heat is lost to the cold air outside.

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"You don't need to plug it in when you get home from work at 5 if you're not leaving until 7 a.m. the next morning," Kulyk says. "Electricity is really cheap in Manitoba but you're just wasting power to keep it plugged in for 14 hours."

For $15 or $20, you can buy a block heater timer so you're not having to run out to plug the car four hours before you use it.

"You can get them at places like Canadian Tire and Home Depot," Kulyk says. "I'm seeing one advertised right now for $10."

If you're only driving one or two days a week in the winter, Kulyk says you should be more worried about your battery losing its charge, especially if it's a few years old.

"If you don't drive very frequently, you can get a battery minder installed," Kulyk says.

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