Why is my car overheating?
Updated 31 Oct 2019
Steam billows from under the bonnet.
The temperature gauge spikes into the red zone, the Check Engine Light blinks at you, and your dashboard message displays ‘ENGINE TOO HOT’.
This can’t be good.
Why is your car overheating?
In one fashion or another, your car overheating signals a problem with the cooling system – that’s no surprise, is it?
Coolant needs to circulate from the hot engine to the radiator, then the cooled fluid cycles right back into the engine.
If something isn’t working as it should – literally, any one thing – your engine temperature can skyrocket.
Radiator Hose Leak
No matter what make or model you drive, there are two radiator hoses: an upper and a lower hose.
They allow coolant to pass from the engine to the radiator, then back again.
A leaking radiator hose can introduce air into the cooling system, and there’s no coolant to transport heat.
A radiator hose leak is one of the more common overheating causes for older cars.
The repair is straightforward, and the cost is definitely among the most reasonable.
You’ll feel like you got away lucky if it’s only a radiator hose leak.
Water Pump Failure
Like a good little turbine, the water pump forces coolant throughout the cooling system.
It really is the heart of the system.
The water pump can have a leak or, worse yet, the impeller can degrade or fail, preventing coolant from circulating.
A faulty water pump is a serious problem and, if not addressed quickly, could turn into a much larger issue.
That turns it from a repair cost of a few hundred dollars into thousands.
Blown Head Gasket
The dreaded cylinder head gasket leak.
It’s a multi-layer seal comprised of durable materials, often stamped steel and composite fibre.
Usually it’s not the root cause of the problem – it’s a symptom that comes up when a problem is left too long.
Engine oil gets into the coolant galleries and coolant gets into the oil.
A blown head gasket is a mess, causes overheating, and it’s a big job to repair.
It’s several hours in labour and a bunch of parts.
Less common than it used to be but still worthy of mentioning is a stuck thermostat.
Designed to regulate the engine’s temperature around 88C or so, it opens and closes to restrict coolant flow.
If it gets stuck closed when the engine is at operating temperature, it takes very little time for the engine to overheat.
The thermostat is typically a minor repair in the scheme of things, with relatively low cost for parts.
If it’s one of the tricky jobs to do, the labour cost can rack up fast.
Poorly maintained cars can overheat also, if the cooling system isn’t serviced on time.
Coolant becomes acidic and deposits form that attach to the inside of the radiator. Restrict the coolant flow and you know what happens next…overheating.
The correction is a replacement radiator in most cases, although minor cases can be fixed with a cooling system flush.
What to Do if Your Car is Overheating
If you see the tell-tale signs of overheating from your car – steam from under the bonnet, a high-temperature reading, or ‘Engine Hot’ message – it’s best not to tempt fate.
Pull over and let your engine cool down.
Have a mechanic diagnose your overheating condition and repair it sooner rather than later.
If you keep driving in a car that tends to overheat, you could find yourself broken down at the roadside, or with additional repairs to the original problem including the worst-case scenario: a seized engine.
Here are some more tips on what to do if your engine overheats.
AutoGuru can help find a great local mechanic to diagnose your overheating issue.
Compare prices and reviews, and book online!
Jason is a Canadian automotive content writer with a background in the auto service industry, but he’s been hooked on cars and mechanics since childhood.
One of his first cars was an ’80 Mazda RX-7 that’s sorely missed to this day. A ’68 Ford Torino GT, a ’66 Ford Country Squire Woodie station wagon, and a ’96 Suzuki GSX-R 750 have spent time in his fleet of cars, bikes, and trucks over the past two decades.
Jason’s pride and joy is under construction – a turbocharged ’88 Mazda RX-7 convertible. Also on his resume is CASCAR official certification.