What to Do If Your Car Engine Overheats
We hunted down car cooling system designers to find out what happens when cars overheat (it's not pretty) and what you can do to help prevent a breakdown.
What to Do If Your Car Engine Overheats
We hunted down car cooling system designers to find out what happens when cars overheat (it's not pretty) and what you can do to help prevent a breakdown.
What to Do If Your Car Engine Overheats
We hunted down car cooling system designers to find out what happens when cars overheat (it's not pretty) and what you can do to help prevent a breakdown.
- Warning lights, steam or a rising temperature gauge are common signs your engine is overheating.
- Pull over immediately, turn off your engine and call for help.
- Avoid touching the radiator cap or pouring cold water on a hot engine — sudden temperature changes can cause damage.
- If towing isn’t an option, wait until the engine is completely cool (30 minutes or more) before checking your coolant level and hoses and adding antifreeze if needed.
- Check hoses for leaks. You’ll probably need a mechanic to figure out why your car overheated and make repairs.
Stop, turn off the car and call for help are the first — and only — steps you should take when your car overheats on the road. Continuing to drive risks engine damage. And trying to fix the problem yourself while the engine is hot is a recipe for burns from scalding coolant.
That’s the advice of two car cooling system designers, Steve Schreck and Drew Conkling. As product managers at a major international auto parts manufacturer, they oversee the development of cooling system components that go into millions of vehicles worldwide. And they know a lot about why excessive heat can ruin an engine — and a road trip.
Here, they provide tips on what to do when your car overheats and suggest basic car maintenance that can help prevent your car from overheating. Like knowing what to do with a flat tire, being prepared for an overheating engine can turn a stressful roadside moment into a manageable one.
Signs your engine is overheating
An overheating engine usually gives you some warning before it causes real damage. Watch for:
- Dashboard warning lights. A temperature warning light or check engine light can be a sign your engine is running hotter than normal.
- A rising temperature gauge. If the needle climbs toward “H” or into a red zone, your engine is overheating.
- Steam from under the hood. Steam escaping from the hood, which can look like smoke, is a clear sign to pull over right away.
- Unusual smells or noises. A sweet smell (coolant) or ticking and knocking sounds can also point to a cooling system problem or overheating.
Your car is overheating. Now what?
Most cars are equipped with warning lights and a pressure relief valve, so if your engine starts to overheat, you'll probably get advance warning before it damages the engine. But don't keep driving. Once you’ve pulled over and called for help, here’s what Schreck and Conkling say to do.
That's it — stop there. "Don't even think about touching the radiator cap while you're waiting for a tow truck," Schreck says. "The cooling system is highly pressurized. Just loosening the cap a little can set off a geyser of hot coolant."
"Also, there's nothing you can do from the side of the road," says Conkling. "Your car needs to be towed to a professional."
If towing to an auto shop is not an option and you have no choice but to take matters into your own hands, consider following these steps:
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Wait until the engine completely cools — at least 30 minutes. You might be able to speed up the cooling process if you can pop the hood with a latch located inside the car cabin. But do not touch or attempt to open the hood until the engine is completely cool.
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Check the coolant/antifreeze reservoir. Typically, this reservoir is a translucent plastic tank near the radiator. If it's empty or low on fluid, and you've allowed time for the engine to cool, refill the tank with new antifreeze.
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Check hoses for leaks or blockage . Chances are, if the coolant tank is completely empty or you spot a drip or puddle on the ground, you've got a leak.
For more tips on staying safe while you wait for a tow, see our guide on how to handle a roadside emergency.
What not to do if your car is overheating
While you wait for help, avoid these actions, which can make the situation worse or put you at risk of injury:
- Don’t keep driving. Continuing to drive with an overheating engine can quickly turn a minor issue into major, costly engine damage.
- Don’t open the radiator cap or hood while the engine is hot. The cooling system is pressurized and opening it too soon can release scalding coolant or steam.
- Don’t pour cold water on a hot engine. Splashing cold water on hot engine parts can cause thermal shock — a rapid temperature change that can crack the engine block, cylinder head or other components.
- Don’t ignore the warning signs. Pulling over as soon as you notice a warning light, rising gauge or steam can help you avoid more serious — and expensive — repairs.
This is why you need to know how your engine's cooling system works?
Technically, here's what's happening: Heat from your engine is absorbed by coolant (think: antifreeze), which the engine's water pump pushes to the radiator, where it cools and is recirculated back to the engine.
Coolant lowers the freezing
point of water, increases its
boiling point and can help
prevent corrosion.
A car engine produces heat when it runs. This heat is absorbed by the coolant flowing through the engine. The water pump pushes the coolant into the radiator, which releases the built-up heat into the atmosphere. Then the coolant flows back into the engine to grab more heat. This is a continuous process that keeps the engine from overheating.
The simple answer? "Think of the water pump as a human heart sending blood throughout the body — it keeps pumping coolant through the engine, then back again," says Schreck. Although engines no longer use water for cooling, the term water pump is still used to describe the system that moves coolant through an engine.
The coolant — the fluid that flows through the cooling system — flows from the engine to the radiator, where heat gets released into the atmosphere. "That's why the technical name for the radiator is the heat exchanger. It takes the heat out of the coolant," says Conkling. "The coolant then flows back to the engine to grab more heat. It's a continuous loop."
This is what happens when it doesn't work?
When something goes wrong in the cooling system, all components in the engine run at a temperature that's too high, Conkling says. "The engine and coolant heat up, and metal keeps expanding the hotter it gets." Parts of the engine can warp or melt, resulting in costly repairs. Depending on the damage, you may even need a new engine.
Hot weather and blasting the AC aren't causing the car to overheat
Conkling puts it this way: If you were speeding through Death Valley in 1973 with the AC blasting, turning it off and slowing your speed might help cool the engine. But modern cars are typically better designed to handle that kind of load, so when your instruments say the car is overheating, the cooling system may be malfunctioning. "No amount of letting it cool off in the shade is going to solve the problem."
Common engine overheating causes.
If your temperature gauge is climbing, a few culprits are often to blame:
- Low coolant. A leak or evaporation over time can leave too little coolant to properly absorb and carry away engine heat.
- A failing radiator fan. If the fan that pulls air through the radiator stops working, your engine can overheat, especially at low speeds or when idling.
- Blocked airflow. Any buildup of material on the front or back side of the radiator (think: leaves, bugs, road debris, snow) can obstruct the flow of air.
- A faulty radiator cap. The cap keeps your cooling system pressurized. If it fails to hold pressure, coolant can boil at a lower temperature than it should.
- A leaking hose. Cracked or loose hoses can leak coolant and let air into the system, reducing how well it cools the engine.
- Thermostat problems. The cooling system’s thermostat works like a heat-sensitive valve. A stuck or failed thermostat can block coolant from flowing when it should.
- Water pump issues. A failing water pump may not circulate coolant fast enough, or at all. Deteriorating pump seals may let coolant leak out, causing overheating.
- A clogged radiator. Debris, rust or scale buildup can restrict flow through the radiator, limiting how much heat it can release.
- Head gasket problems. White smoke from the tailpipe, milky-looking oil or unexplained coolant loss can sometimes point to a blown head gasket — a repair that typically requires a mechanic’s diagnosis to confirm.
Chances are, you need a mechanic to tell you why the car is overheating
Why? Schreck explains, by way of a breakdown he experienced. "I had a 2005 car that started blowing coolant all over the road," he recalls. "My mechanic ran a diagnostic test and found the issue was a small defect in the radiator cap. You're not going to pinpoint something like that without testing on sophisticated equipment."
Pro tips to help prevent a car from overheating
Schreck and Conkling offer this advice for preventing a costly meltdown.
- Coolant picks up dirt and particles that decrease its effectiveness. Coolant that looks cloudy or rusty needs to be replaced. Check the appearance of coolant at every oil change.
- Regardless of how coolant looks, it should be replaced as often as recommended by the manufacturer of your car, typically every two to five years. (See your owner's manual.)
- Use the type of coolant specified by the manufacturer — as in chemical type, not merely brand. Each type contains a different blend of corrosion inhibitors; using the wrong one can damage your cooling system.
- When in doubt, take your car to a professional. Full-service repair shops have access to the latest manufacturer recommendations and have all types of coolant on hand.
Regular maintenance is one of the best ways to help avoid engine overheating, but breakdowns can still happen. Having the right car insurance in place, including roadside assistance coverage, can help with costs of roadside incidents.
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