How Block Heaters Work: What You Need to Know

In Canada, we know electric cars aren't the only ones that need to plug into an outlet sometimes

Just as athletes stretch their muscles before they perform, vehicle engines are happiest when they’ve been given a bit of a warmup before they’re started on very cold days. That’s the job of the engine block heater.

It was invented in 1947 by Andrew Freeman, who’d lived through enough winters in North Dakota when he ran down his Ford’s battery trying to start it in the bitter cold.

He used an electric heating element to warm the fluids in the engine, and while his rudimentary design has been improved over the years, block heaters still work on the same basic principle.

The name “block” heater refers to the lower part of the engine, known as the block. Thanks to gravity, oil collects in the pan at the bottom of the block when the engine’s shut off. Not all heaters go into the block, but most people use the term anyway.

Oil gets thick as it gets cold. This makes it harder to start the engine since the moving parts have to overcome this resistance — and any extra cranking time will use more battery power.

It also takes longer for the oil to get up to the top of the engine, and even though it’s only for seconds, that increases engine wear. Synthetic oil flows better than conventional oil and helps to prevent this, but it can only do so much when the thermometer drops deep into negative temperatures.

Block heaters aren’t necessary in milder climates, but if the temperature falls below about -15°C, they’ll make a difference for your engine’s start-up, whether it’s first thing in the morning or if it’s been sitting outside all day at your workplace.

Most types of block heaters actually warm up the engine coolant rather than the oil, but this also warms up the engine, which in turn takes the chill off the oil. Some are located in the lower rad hose, while others are screwed into the block through an expansion plug hole.

Also known as “freeze plugs,” the popular story behind expansion plugs is they’re meant to protect your engine if it’s cold enough that your coolant freezes: the plugs pop out so the ice doesn’t expand inside and crack the engine block.

That’s the theory, but even in rare circumstances where an engine freezes, they don’t always pop out as planned. In reality, it’s because engines are sand-cast, with a die pressed into sand to make a mould that’s then filled with molten metal. The holes are part of the mould, and the sand is shaken out of the engine casting through them.

The rad hose or expansion plugs are the most common locations for factory-installed block heaters. Other types include heaters that go into the engine oil dipstick tube; oil pan or engine heaters held on with magnets or glue; heaters that screw into the oil pan drain hole; and electric blankets that go over the top of the engine and are removed before you drive away.

There are also transmission heaters, which warm up the fluid to help the unit shift gears more easily and efficiently, as well as battery heaters to keep these warm for better starting power, although they’re generally far more popular on work trucks than on everyday passenger vehicles.

Thanks in part to improvements in engine oil, and in the cost of including something that most people don’t use anyway, automakers are more likely to list block heaters as extra-charge options rather than a standard feature.

If you’re adding an aftermarket one, then unless you’re really handy around a tool chest, get it professionally installed if it’s the type that goes into the engine block or cooling system, to help avoid the potential for leaks.

The block heater plugs in using its attached cord, and if it’s your first time using it, you’ll have to find the cord under the hood. While it may be convenient to simply plug it in before you turn in for the night, the heater only needs to be on for about three or four hours to do its thing. Installing and setting a timer on the outlet will cut down on the amount of electricity used. Don’t forget to unplug it before you drive away in the morning (don’t ask how we know this).

In addition to component protection, an engine that’s already been warmed a bit by a block heater will come to operating temperature quicker, saving on fuel and emissions.

Whether you use a block heater or not, once you’ve started your vehicle, don’t let it sit and idle until it’s fully warmed up. It’s running richer than usual, and because it’s just idling, unburned fuel can wash away oil in the cylinders and result in engine wear.

A modern engine actually warms up faster when it’s being driven. Start it, let it idle for a minute or so, and then drive moderately for the next few kilometres, accelerating smoothly instead of stomping on the throttle. That quicker engine warmup also means your heater will blow hot air sooner, and both you and your engine will be better off for it.

· Professional writer for more than 35 years, appearing in some of the top publications in Canada and the U.S.

· Specialties include new-vehicle reviews, old cars and automotive history, automotive news, and “How It Works” columns that explain vehicle features and technology

· Member of the Automobile Journalists Association of Canada (AJAC) since 2003; voting member for AJAC Canadian Car of the Year Awards; juror on the Women’s World Car of the Year Awards

Jil McIntosh graduated from East York Collegiate in Toronto, and then continued her education at the School of Hard Knocks. Her early jobs including driving a taxi in Toronto; and warranty administration in a new-vehicle dealership, where she also held information classes for customers, explaining the inner mechanical workings of vehicles and their features.

Jil McIntosh is a freelance writer who has been writing for Driving.ca since 2016, but she’s been a professional writer starting when most cars still had carburetors. At the age of eleven, she had a story published in the defunct Toronto Telegram newspaper, for which she was paid $25; given the short length of the story and the dollar’s buying power at the time, that might have been the relatively best-paid piece she’s ever written.

An old-car enthusiast who owns a 1947 Cadillac and 1949 Studebaker truck, she began her writing career crafting stories for antique-car and hot-rod car club magazines. When the Ontario-based newspaper Old Autos started up in 1987, dedicated to the antique-car hobby, she became a columnist starting with its second issue; the newspaper is still around and she still writes for it. Not long after the Toronto Star launched its Wheels section in 1986 – the first Canadian newspaper to include an auto section – she became one of its regular writers. She started out writing feature stories, and then added “new-vehicle reviewer” to her resume in 1999. She stayed with Wheels, in print and later digital as well, until the publication made a cost-cutting decision to shed its freelance writers. She joined Driving.ca the very next day.

In addition to Driving.ca, she writes for industry-focused publications, including Automotive News Canada and Autosphere. Over the years, her automotive work also appeared in such publications as Cars & Parts, Street Rodder, Canadian Hot Rods, AutoTrader, Sharp, Taxi News, Maclean’s, The Chicago Tribune, Forbes Wheels, Canadian Driver, Sympatico Autos, and Reader’s Digest. Her non-automotive work, covering such topics as travel, food and drink, rural living, fountain pen collecting, and celebrity interviews, has appeared in publications including Harrowsmith, Where New Orleans, Pen World, The Book for Men, Rural Delivery, and Gambit.

2016 AJAC Journalist of the Year; Car Care Canada / CAA Safety Journalism award winner in 2008, 2010, 2012 and 2013, runner-up in 2021; Pirelli Photography Award 2015; Environmental Journalism Award 2019; Technical Writing Award 2020; Vehicle Testing Review award 2020, runner-up in 2022; Feature Story award winner 2020; inducted into the Street Rodding Hall of Fame in 1994.

Email: [email protected]

Linkedin: https://www.linkedin.com/in/jilmcintosh/

Twitter: https://twitter.com/JilMcIntosh

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