Why is my car overheating?

First: what to do right now

1. Pull over somewhere safe as soon as you can, with your hazard lights on. On a motorway or highway, take the next exit or service area if you can reach it safely.
2. Turn the engine off.
3. Get everyone out and away from the road.
4. Wait at least 30 minutes before opening the hood or touching anything. Do not open the radiator or expansion tank cap while it is hot.
5. When it is cool, check the coolant level in the expansion tank and look under the car for a leak. If the level is low, top up (see the FAQ below) and watch the gauge closely.
6. If it overheats again, or you see a big leak or steam, call for recovery rather than driving on.

Signs that your engine is overheating: the temperature gauge in the red or the engine temperature warning light, steam from under the hood, a sweet smell of hot coolant, or a sudden loss of power.

Likely causes, most common first

1. Low coolant from a leak

   The most common cause. Coolant can leak from a hose, the radiator, the water pump or the heater. Look for green, yellow, pink, orange or blue fluid with a sweet smell under the front of the car. If the level keeps dropping with no visible leak, it may be leaking inside the engine (see head gasket below).

   Read the fix guide →

2. Thermostat stuck closed

   The thermostat is a valve that opens when the engine warms up to let coolant flow to the radiator. If it sticks shut, coolant cannot reach the radiator and the engine overheats even with the coolant full.

3. Cooling fan not working

   The electric fan pulls air through the radiator when you are moving slowly or stopped. If it fails, the car overheats in traffic but may be fine on the open road. A blown fuse, a relay or the fan motor itself can be to blame.

4. Water pump failure or a broken drive belt

   The pump moves coolant around the engine. A worn pump can leak or stop circulating; on many cars it is driven by a belt, and if that belt snaps, the pump stops too. A squealing belt or a leak from the front of the engine are clues.

5. Blocked or damaged radiator

   Rust, debris, the wrong coolant or a damaged radiator cap can stop the radiator shedding heat. Leaves or dirt blocking the front of the radiator can do the same.

6. Head gasket failure

   Often the result of overheating rather than the first cause, but it keeps the problem going. Signs: coolant disappearing with no leak, white sweet-smelling exhaust smoke, bubbles in the expansion tank, or a creamy layer under the oil filler cap.

7. Low engine oil

   Oil helps carry heat away from the engine. Very low oil makes it run hotter and wear faster. Check the level once the engine is cool.

What it costs to fix

It depends entirely on the cause, and on the car. Topping up coolant and replacing a split hose are usually among the cheaper repairs. A thermostat replacement on a small car is typically a few hundred dollars: RepairPal estimates $351–$431≈ £270–£340≈ €320–€390≈ A$530–A$650 for a Mazda 2 and $297–$353≈ £230–£280≈ €270–€320≈ A$450–A$530 for an older Honda CR-V, while on some heavy-duty pickups it is well over $1,000. A water pump costs more, because it often takes several hours of labor. A head gasket is one of the most expensive engine repairs, which is why stopping early matters so much. Ask for a written estimate and a diagnosis, such as a cooling system pressure test, before any big job.

DIY or garage?

How to prevent it

• Check the coolant level in the expansion tank regularly, with the engine cold, and top up only with the coolant your owner's manual specifies.
• Watch the temperature gauge, especially in hot weather, heavy traffic or when towing.
• Look under the car where you park for new drips, and get any sweet-smelling leak checked.
• Have the coolant changed at the interval in your owner's manual.
• Keep the engine oil at the right level.
• Ask your garage to check hoses, belts and the radiator cap at each service.