By Porter Lang
A cord comes out of the grille of a parked car and runs to an outlet. It is not a charging cable. It is a block heater, and the sources disagree, politely, about how long to leave it on.
What it is
Natural Resources Canada, the federal department, describes the device in plain terms. A block heater warms the coolant, which in turn warms the engine block and its lubricants, so the engine starts more easily and reaches its proper operating temperature faster. The department explains why that matters. In a cold engine the oil is thick and resists flow, so the engine works harder against internal friction. Combustion is less efficient, the air-fuel mixture is richer, and the catalytic converter does not work well while it is cold. The result, it says, is more fuel burned and a sharp increase in emissions in the first minutes after a cold start.
A block heater runs on electricity. The page we read is dated 2008 in its page data, so treat its figures as the department’s at that time. It says that at minus 20 degrees Celsius a block heater can improve overall fuel economy by as much as 10 percent, and that for a single short trip at minus 25 the saving could be in the order of 25 percent.
When to plug in
The Alberta Motor Association, a motoring club, gives a threshold. Most vehicles are fine until minus 15, it says, but once it is colder than that you should plug in. Its 2018 news release repeats the number as its recommendation.
BEMAC, a Canadian business whose blog covers car care, gives a wider band. It says most experts suggest plugging in at about minus 15 to minus 20 degrees Celsius, that newer fuel-injected cars can start at minus 30, and that older cars may benefit at freezing. It also says diesel engines may need plugging in at warmer temperatures. We have not checked those last claims against a second source and label them as the blog’s.
A summary page, Garagemap, says that CAA Quebec suggests plugging in below minus 5 and calls it highly recommended at minus 15 or colder. We saw that only secondhand.
How long to leave it on
This is where the sources split.
| Source | Time before driving |
|---|---|
| Natural Resources Canada (2008 page) | A timer set to switch on two hours before you leave, “Usually this is all the time needed” |
| Alberta Motor Association, how-to article | About 4 hours, using an electrical timer |
| Alberta Motor Association, 2018 release | At least four hours when it is colder than minus 15 |
| BEMAC blog, quoting a Manitoba motor club | Four hours around minus 30; longer does not help because heat is lost to the cold air after about four hours |
We do not resolve the two-hour and four-hour figures. Our reading: the colder the morning, the longer the heater needs, but none of these pages tests that, and the department’s page is dated 2008, ten years before the motor club’s release. All of the sources agree on one thing: the engine does not need heating all night. The Alberta how-to article says so directly. NRCan suggests a timer to avoid leaving it plugged in all night, and the blog adds that overnight use only adds to the power bill.
Finding the plug
The Alberta article says different vehicles keep their block heater plug in different places, and advises learning where yours is as soon as you get the car, because the first time you need it will probably be dark and cold. The BEMAC blog says the cord usually hangs from the grille or sits just inside the hood, and may be hidden under a cap. It plugs into an outdoor-rated, three-wire extension cord connected to an outlet.
The motor club’s survey shows how many drivers know this. In an online survey of 2,304 Albertans, fielded between 22 and 29 October 2018, 87 percent said they know where to find their cord.
What the survey found
The Alberta Motor Association says seven in 10 respondents did not follow its recommendation to plug in at minus 15. Of that group, 29 percent waited until minus 20, 11 percent until minus 25, five percent until minus 30, and 27 percent said they never plug in. Only 19 percent said they plug in at minus 15, and eight percent at minus 10. Across all respondents, 30 percent had had a vehicle fail to start because they did not plug it in. The release is a motor club’s own survey, dated 2018.
The club also reports a cold snap in December 2017. It says its roadside team handled more than 2,600 battery problems on 26 December and more than 12,500 between 26 December and 1 January, which it calls the equivalent of a month of winter battery calls.
If you do not have one
The motor club says that if your vehicle does not have a block heater, switching to synthetic oil in winter will help the engine turn over. The BEMAC blog says you may not need one if your car uses synthetic oil or is parked in a heated garage or well-sheltered place.
Safety
The blog says block heaters are generally safe, but damaged cords or poor connections can cause an engine fire. It advises checking cords for fraying, cracks and salt corrosion, not driving over the extension cord, and unplugging the heater before driving away. We give no installation advice. The sources say to ask a mechanic.
Dates in order
- 2008 (Natural Resources Canada page data): the federal article on block heaters.
- December 2017 (motor club release): the cold snap with record battery calls.
- 22 to 29 October 2018 (motor club release): the survey of 2,304 Albertans.
- 2 November 2018 (motor club release): the news release.
What kind of sources these are
A federal department page, a provincial motor club’s article and news release, a business blog and a summary site. The motor club and the blog are not neutral: one is a membership body and the other a business’s own page. The government page is old.
Questions a buyer would ask
Does a rental car have a block heater? The sources we read do not say. Our reading: ask at the counter before a winter road trip.
Is a block heater the same as an engine warmer for an electric car? The sources we read are about engines with coolant. They do not cover electric vehicles.
What we left out
Prices, brands, installation instructions, anything about oil pan heaters beyond a word, battery tests and the club’s membership offers, and any claim that Sephari stocks, sells or ships heaters or cords.
Quick answers
At what temperature should you plug in a block heater? The Alberta Motor Association says most vehicles are fine until minus 15, and it recommends plugging in once it is colder than that.
How long should a block heater be plugged in? Natural Resources Canada suggests a timer set two hours before driving. The Alberta Motor Association suggests about four hours.
What does a block heater do? According to Natural Resources Canada, it warms the coolant, which warms the engine block and oil, so the engine starts more easily and reaches operating temperature faster.
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