Why is my car overheating?

I RECENTLY became the owner of a 1996 VW Golf. The car is running well, except for a baffling overheating problem.

I RECENTLY became the owner of a 1996 VW Golf. The car is running well, except for a baffling overheating problem.

It never overheats in stop-start town driving but at freeway speeds the temperature goes right up to the red zone, even in cool weather.

A friend helped me to flush the radiator but it made no difference. The previous owner says he replaced the water pump about a year ago.

Do you have any suggestions as to what might be causing the overheating? Is it a good idea to remove the thermostat as some people have said I should do?

Patrick, e-mail

Patrick, overheating is one of the most common of all car troubles. Finding the cause can be the devil of a problem.

From what you say it seems likely that the coolant is not circulating freely at high speeds.

If the water pump is nearly new it should be able to do its job of circulating the coolant efficiently. So there must be some restriction to the flow of coolant. The main suspects are:

lClogged radiator tubes. I know you have flushed the radiator but backflushing or chemical cleaners often fail to shift hardened deposits inside the tubes.

lCollapsing bottom radiator hose. The suction on the inlet side of the water pump can make the bottom hose collapse.

An old hose, softened by heat and without the spiral of spring wire inside it to prevent the hose from collapsing is prone to this.

Try to get a good view of the bottom hose when the engine is hot and the revs are suddenly increased. You will see it flattening if this is the problem. You can also squeeze the hose (when it has cooled down sufficiently!) to feel if it's soft and flabby.

l Defective thermostat. Thermostats can get lazy, fail to open at the correct temperature, get stuck halfway open.

"Pirate" thermostats have a bad reputation in this regard. You can test whether the fault lies with the thermostat by removing it temporarily. If the overheating stops you have found the culprit .

Simply discarding the thermostat and running an engine on a permanent basis without thermostat is one of the worst things you can do to an engine.

The thermostat is the traffic cop that decides when the coolant is permitted to circulate.

Replacing it with a new one every five years is excellent preventative maintenance.