Do You Need a Block Heater in Ontario?

If your vehicle has one and it sits outside overnight, yes — use it once it drops below about –15°C. A block heater doesn’t make a car start that wouldn’t otherwise; it makes every cold start easier on the engine, the battery and the starter, and it gets you heat sooner. On a modern car in a heated garage it’s optional. On an older truck parked in the driveway in January it’s the cheapest engine protection you can buy.

What a block heater actually does

It’s a small electric element, usually screwed into the engine block or clamped to a coolant hose, that warms the engine coolant and by extension the block and the oil around it. Plugged in for a few hours, it raises the engine temperature by a useful margin — not to operating temperature, but enough that the oil flows on the first turn instead of sitting like syrup while the bearings run dry for the first seconds. That first cold minute is when most engine wear happens, so warming the block matters more than it sounds.

The side effects are the ones people notice: the battery has to push a lot less to turn a warm engine, the engine catches quickly rather than cranking, and the heater blows warm sooner because the coolant has a head start.

When it’s worth plugging in

A common rule of thumb is anything below –15°C, and it becomes more important the older the engine, the thicker the oil, and the weaker the battery. Diesels want it warmer still. In a Woodstock winter that’s a few weeks of real use most years and a lot more in a cold one. Above –10°C, a healthy engine on modern synthetic oil doesn’t need the help.

How long to leave it plugged in

Two to four hours before you leave is the useful range. The block reaches its steady temperature within a few hours; after that you’re paying for electricity without warming anything further. A cheap outdoor timer on the outlet, set to come on around 4 a.m. for a 7 a.m. start, is the answer — and it means you don’t forget.

Does your vehicle have one?

Many vehicles sold in Canada have a block heater fitted at the factory or the dealer, with the cord tucked behind the grille or tied up near the battery. Look for a short black cord with a three-prong plug. If there’s no cord, there may still be a heater with the cord removed, or none at all — it’s worth a look under the hood or a question when the vehicle is in for service.

Using it safely

• Use an outdoor-rated extension cord, heavy enough for the load, and keep the connection off the wet ground.
• Check the cord for cracks or corrosion on the plug each fall; cords get run over and chewed.
• Unplug before you drive. Everyone forgets once.
• If the heater trips the breaker, stop using it and have it looked at — a failing element can leak coolant into the wiring.

Common questions

Can I leave it plugged in all night?

You can; it’s thermostatically limited and won’t overheat. It just wastes power past the first few hours. A timer is better.

Will a block heater fix a car that won’t start in the cold?

It helps a marginal battery get over the line, but it’s not a substitute for a battery that’s at the end of its life. If it wouldn’t start without it, find out why — see why your car won’t start in the cold.

Do electric vehicles and hybrids need one?

EVs precondition their battery from the app instead. Hybrids with a gas engine sometimes have one and benefit the same way any gas engine does.

Is a remote starter as good?

Different job. A remote starter warms the cabin; a block heater warms the engine before it turns over. The block heater is the one that protects the engine.

This article is part of our guide to winter driving in Oxford County. If you’re not sure whether your vehicle has a block heater, or whether it works, ask when it’s in for its fall oil change — or book an appointment.