Function

The cooling system seldom breaks down during high-speed highway driving. Mostly it happens in a traffic jam or in town driving which causes the engine with a defective cooling system to boil. In this case one should search very quickly for a safe place to stop. Should you however, already stressed out, reach, immediately after opening the bonnet, for the screw-down radiator cap, the problems really begin. The first thing to do is to allow the radiator to cool down properly. Then using enough rags to ensure that you don't burn your hands, determine carefully whether or not the cooling system is still under pressure. One cannot pour cold water into a hot system anyway. The question is, whether you can get the car mobile again by refilling the radiator or e.g. ruin the engine completely. More about this subject below on this page.

How it works

In the search for the reason why an engine with sufficient coolant constantly overheats, your own hands as 'temperature sensors' can help. If the engine is cold and warms up slowly, the short circuit circulation must also warm up slowly and the radiator circulation should remain cold, otherwise the thermostat does not close properly. If the engine is hot and the radiator remains cold, then the thermostat is not opening. At some point the fan must start running when the engine is idling. Please, during this test, pay careful attention to the temperature gauge, to avoid any further damage.

Should everything function correctly and the engine still overheat during travel, then either an insufficient flow amount or the heat transference is too low. The radiator could possibly be blocked or be clogged with dirt from the outside. Other parts of the cooling system can be restricted by blockage. It is possible that the water pump performance is failing. All these checks are made assuming that the water level in the reservoir is between minimum and maximum, and that by letting the motor run for a long period without the radiator cap, there is no air in the cooling system.

It becomes bad if you have already driven too long with an overheated system. In case you did not keep an eye on the engine temperature, older petrol engines without a knocking sensor start to 'ring' which is a sure warning sign that something bad is on its way. The cylinder head distorts stronger than the engine block, and the cylinder head gasket can no longer hold the coolant. If too much of it reaches the combustion chamber heavy damage is certain. In this case water has about the same effect as a piece of metal (e.g., a screw) which has found its way into the engine. Only very seldom is one lucky and the engine is airtight after cooling down again. Mostly the cylinder head must be dismantled and examined for evenness. One can compensate a few tenths of millimetre by planing (see picture). A half a millimetre or more generally means an exchange. 07/08

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