A car engine overheats when the cooling system is unable to absorb, transport, and dissipate heat from the engine.
Overheating can be caused by a number of different problems, including:
- Low coolant level – If coolant has not been topped up regularly or is leaking from an external or internal source, the engine will overheat.
- Fan failure – Whether the cooling fan is electric or belt-driven, if it stops working for any reason then overheating will occur.
- Faulty thermostat – The thermostat opens and closes in response to temperature. If it fails to open, coolant cannot circulate and the engine will overheat.
- Clogged radiator – If the radiator becomes clogged with insects, rust or other debris, it will not circulate air properly, causing overheating.
- Restricted exhaust – If the catalytic converter on an exhaust pipe has been crushed, exhaust flow away from the engine also becomes restricted, resulting in overheating.
What happens when a car overheats?
When a car overheats, it can cause major damage to your engine. Results of overheating can include:
- Damaged rings, pistons and rod bearings.
- Piston scuffing, which damages both the pistons and the cylinders.
- Loss of compression due to sticking exhaust valves.
- Blown head gasket, causing compression leaks and coolant leaking into the cylinders.
- Seized or broken overhead cam.
The results of an overheated engine can be extreme and can lead to very expensive repairs, which is why a vehicle should be parked and allowed to cool down as soon as it begins to show any signs of overheating.
What to do when a car overheats?
If your car overheats, you should stop immediately. Never continue to drive, or you may permanently damage your engine.
When overheating occurs:
- Park your car and let the engine cool down. Turn the engine off, as idling will make it even hotter.
- Open the bonnet to allow air to circulate, but DO NOT open the radiator cap until the engine has cooled down or you may scald yourself.
- When the engine is cool, check the coolant level and if low, top it up. If you don’t have coolant with you, tap water can be used, providing you have your cooling system flushed at a later date.
- Look for leaks around and under the engine bay. If there is nothing obvious such as a burst radiator hose, call for a mobile mechanic. Don’t be tempted to drive your car to the nearest servo.
How to prevent a car from overheating?
Regular maintenance of your car’s cooling system is the best way to prevent your engine from overheating. At the very least, you should check the coolant level periodically and top it up if required.
If you don’t mind getting your hands dirty and you are experiencing an intermittent overheating problem, you can try the following things to determine the cause:
- Check the thermostat – Either run the engine and feel the upper radiator hose to see if it gets hot (which indicates that the thermostat is opening correctly), or remove the thermostat and place it in boiling water to see if it opens. If it doesn’t, it should be replaced.
- Check the head gasket – Run the engine and check the exhaust. If white steam is coming out, your head gasket is leaking.
- Check the cooling fan – Inspect the fan for signs of oil around the clutch or a tendency for the fan to wobble or to spin freely when the engine is off, as this could indicate a faulty fan clutch.
- Check belts and hoses – A slipping belt could prevent the water pump from working properly, and a collapsed radiator hose could prevent coolant flow, so check and replace these as required.
- Flush the radiator – Back-flush the cooling system to remove rust and hard water scale. Be aware that any time you open the cooling system to service it, you will need to purge it when you have finished, as air pockets can develop, which can cause overheating. Simply use the bleeder valve found on most cooling systems or temporarily loosen a heater hose to get the air out of the system.
