If the engine overheats, the first thing that will happen is a gasoline engine will start to detonate. The engine will ping and start to lose power under load as the combination of heat and pressure exceed the octane rating of the fuel. If the detonation problem persists, the hammer-like blows may damage the rings, pistons or rod bearings.

Overheating can also cause pre-ignition. Hot spots develop inside the combustion chamber that become a source of ignition for the fuel. The erratic combustion can cause detonation as well as engine run-on in older vehicles with carburettors. Hot spots can also be very damaging and burn holes right through the top of pistons.

Another consequence of overheating may be a blown head gasket. Heat makes aluminium swell almost three times faster than cast iron. The resulting stress can distort the head and make it swell in areas that are hottest, like those between exhaust valves in adjoining cylinders, and areas that have restricted coolant flow, like the narrow area that separates the cylinders. The typical aluminium head swells most in the middle, which can crush the head gasket if the head gets hot enough. This will cause a loss of torque in the gasket allowing coolant and combustion leaks to occur when the head cools.

Common Overheating Problems

1. Radiators - Older copper and aluminium radiators tend to get clogged, restricting the flow of coolant.
2. Thermostats - Either installed improperly or sticking closed.
3. Water pumps - Failure to replace older or failing pumps or install a new pump properly.
4. Heater core leaking - A common problem.
5. Coolant leaks from either hose connections or from the cylinder head due to overheating.
6. Bad radiator hoses or belts.
7. Cooling systems are often neglected - If coolant isn’t changed, the coolant passages can experience build up of scale and sludge and coolant won’t flow rapidly enough to cool the engine. Coolant should be changed at least every two years or 30,000 miles or it will lose its effectiveness, and the mixture of antifreeze and water should always be 50/50. A mixture with more than 50 percent antifreeze will cause the coolant to not perform properly, and with less than 50 percent, the engine can freeze and crack. Also, the system needs to be flushed when the coolant is changed. Oil must also be changed regularly too. Old, dirty oil won’t flow as quickly and will hamper cooling.