When Should You Plug in Your Car’s Block Heater?

toy car with electrical plug

We all know Canadian winters can be rough. They can be particularly harsh on your car. With our -20° Celsius temperatures, there are many reasons you’ll want a warm car when it’s not in use, including personal comfort!

You can, however, actually improve your car’s fuel efficiency, keep gas emissions lower and reduce engine wear and tear. What’s the best way to do that? Using a block heater warm your car before turning the key in the ignition.

What’s a Car Block Heater, Anyway?

When you start your car’s engine, oil passes through the engine block, lubricating moving parts. When the temperature dips well below freezing, the oil thickens and gets gooey. It becomes harder to pass through your engine. If not enough oil is running through the engine, the engine has to work harder. This can wear out your engine parts.

A car block heater is a little electric heater inside your engine. It keeps the engine block toasty, and its coolants and oil warm. Plugging in your car using the block heater makes it run more smoothly when it’s extremely cold. Some block heaters run directly off of the car’s fuel or diesel supply. Most block heaters, however, use electrical plugs.

This YouTube video from the Alberta Motor Association is a good, short overview of what a block heater is:

The block heater’s cord sometimes hangs out of the car’s grill, but also can be found just inside the hood. This cord plugs into an external extension cord, which you plug into an electrical outlet in turn. The block heater cord, however, might be tough to see and find. That’s because newer cars have a cap for the electrical prongs to make the cord safer.

There may be another reason you can’t find the plug, though. Block heaters aren’t usually factory installed anymore on some newer models and imports. You might have to go out and buy one. If you don’t know how to install one, it’s best to call the experts such as Bemac to do it for you.

What Are the Benefits of a Block Heater?

Natural Resources Canada (NRC) says a block heater can lower your car’s emissions and gas bill. Your fuel economy may improve by as much as 10 percent. The Canadian Automobile Association (CAA) says you’ll save 15 percent in fuel consumption over the first 20 kilometers you drive. If 100,000 drivers only plugged their car in once during winter, 50,000 litres of fuel would be saved. That’s a full tanker truck’s worth of gas.

Your car will also take about half the time to be comfortably warm when it has been plugged in. Your car will be warm in about five minutes after starting it if you use the block heater. Otherwise, expect it to take 10 minutes to warm up.

Do I Even Need a Block Heater?

You may not need a block heater if:

  • Your car uses synthetic oil. Synthetic oil is made from artificial compounds and is used in extreme weather conditions. 
  • You park your car in a heated garage or in an area with really good, warm shelter.

You may need a block heater, however, if:

  • Your car uses non-synthetic oil.
  • You park outside in temperatures colder than - 10° Celsius.

Before you buy a block heater, though, you may want to consider other issues with your car first. If you only drive a day or two per week in winter, your battery will lose its charge. This is a bigger issue than keeping your engine warm, especially if you have an older battery. You can get a battery minder put into your car to alleviate this.

Can’t I Just Idle the Car to Warm It Up?

Not on newer model cars built since the 1980s. This post explains why idling a newer car isn’t such an *ahem* hot idea.

How Cold Should It Be Before I Plug In My Car?

Most experts say that you should plug in your car when the temperature gets to about -15° or -20° degrees Celsius. Your car, if it’s a newer model that is fuel-injected, will start when it’s -30° C. It may just throw a bit of a hissy fit, which makes plugging in your car in colder weather a good idea. It’ll save friction on the engine -- another benefit.


Driving.ca goes a step further and suggests plugging in your car when the temperature hits freezing. This may be truer of older cars that aren’t fuel injected. However, block heaters seem to work best for most people in really cold weather. Otherwise, using the block heater when it’s fairly mild may waste energy.


If you have a diesel engine, though, you may have to plug in the block heater at a warmer winter temperature. Diesel engines can be harder to start in even slightly cold weather. Consult an auto repair shop, such as Bemac, for more information.

How Long Should I Use the Car Block Heater?

The jury is sort of out on this one. The NRC suggests plugging in a car for colder weather two hours before you drive. The CAA in Manitoba, where things can get mighty cold, says that two hours isn’t long enough. This is especially true when the temperature is -30° C. They recommend plugging in your car for four hours when the temperature is that frigid.


Should you plug your car in longer than four hours? You can, but it won’t have any benefits. A University of Saskatchewan study in 1972 found that heat in your car is lost to the outside cold air after four hours. Plugging in your car overnight, therefore, will give you no extra boost and will only eat into your power bill.


If running out to your car four hours before commuting is just not tenable, buy a block heater timer. It might be a really good investment, if you don’t want to wake up extra early just to plug in your car.

Can a Block Heater Hurt My Car?

Block heaters are generally safe. It’s the cords you have to worry about. If your cords are damaged or don’t have a good connection, an engine fire can result. Not to scare you, but it doesn’t take long for a car to entirely go up in flames.


Experts say you should use a three-wire, three-pronged extension cord for your block heater. Make sure it has a good rating for outdoor winter use.


Check your block heater and extension cords regularly. Make sure the cords are not frayed, cracked or there’s no corrosion from salt on the block heater plug. Don’t drive over your extension cord. And, for goodness sake, don’t drive away when the car is still plugged in. Unplug the block heater before you start your car.

Want to Learn More About Caring for Your Car in Winter?


We’ve got several articles on winter car care that we hope you find useful:

Drop here!

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