I just moved back to Alberta after 25 years in the United States. Do modern cars still have to be plugged in during the winter? If they do, then at what temperature should I do it? Does it need to be minus 40 degrees Celsius or are there any benefits to plugging in when it’s closer to zero? – Blake, Calgary
If you never want to be stopped cold before you get started, plug in your car once the weather hits 15 below, a driving expert said.
“When the overnight temperature hits minus 15 [Celsius], you should plug in your vehicle,” said Ryan Lemont, manager of driver education for the Alberta Motor Association (AMA). “You can plug it in sooner than that, but you’ll see real benefits of a block heater around minus 15.”
When you plug in your block heater, it warms the engine coolant, which warms the engine block and oil.
“The oil that’s in the engine is the same temperature as outside, so it gets more viscous and it’s harder for the engine to turn over when you start it,” Lemont said. “The block heater just keeps everything a bit warmer – it helps you get to operating temperature quicker.”
Even though minus 15 might not be so cold that your car won’t start at all, starting it when it’s that chilly is hard on the engine, Lemont said.
At that temperature, the oil starts to thicken and doesn’t flow normally. That means more friction – so engine parts start wearing faster than they should. It’s also hard on your car’s battery, he said.
Modern vehicles can often start without being plugged in at minus 30 or even minus 40 – but they won’t like it, Lemont said.
“You have to think of what’s happening to the engine,” he said. “If you plug it in, there’s less drama when you go to start it – you can just have more confidence that you can walk up to your vehicle and it will start.”
Plugging in your car also helps the interior warm up faster, Lemont said. That’s because it heats the coolant, which then warms the interior of your vehicle.
If you plug in your car when it’s warmer than minus 15 outside, it might get toasty inside a little faster – but your engine won’t see any benefits, he said.
In fact, some modern block heaters have a built-in thermostat and won’t start until around minus 15 or colder.
So, do you have to leave it plugged in all night? You can, Lemont said – but if you have a timer and want to use less power, you can set it to turn the heater on three to four hours before you want to leave.
“Three or four hours is what you need for optimal block heater performance,” he said. “But it’s acceptable to let it run all night.”
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