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Our 1998 Kia Sportage has become prone to boiling on a long climb, and lately, just with a warm following wind.

The vehicle has been regularly serviced only by the selling firm although they are no longer Kia agents. The Service Manager has pressure tested the cooling system, speed flushed the radiator and engine, checked the thermostat, temperature gauge and viscous fan hub operations.

The problem appears, on reflection, to have started following replacement of the timing belt and the fitting of a new thermostat, about 2 years ago, and is becoming worse with time.

The car is doing a low mileage as it is now the second vehicle, but is kept for its (amazing) off-road ability and comfort for long trips.

What more can I advise the service manager to check?

Roy

From the "Ask jack" archives - 27 November 2009

I doubt the replacing of the timing belt is connected with an overheating problem unless the engines performance has been affected which you would have noticed straight away.

Overheating is the worst possible issue you can have with an engine as it can eventually cause major damage so you need to get to the source of the problem.

I'm not sure what a radiator speed flush is, but what I would definitely make sure the radiator has no blockages in the core itself. This may require both top and bottom tanks to be removed to check properly. The pressurised radiator cap is another item which can be easily overlooked when checking for an overheating problem.

A test on the head gasket would also be wise. This can be done by checking for hydrocarbons in the cooling system (when the engine is hot) and most garages have the equipment to do this.