QuestionI drove the car this morning and within 5 minutes the temperature gauge 'red lined'. How can I test whether the water pump has gone? If it is not the water pump, what else could cause the engine to overheat so quickly?
AnswerHi Michael. That really is quick. I very much doubt that it is the water pump. Failed pumps do not cause a rapid temperature rise. Normally, pumps fail by leaking. My guess is the cooling system does not have enough coolant in it, or the thermostat has failed.
Have you recently drained and re-filled the system? When re-filling the system, did you turn the heater knob to HOT and run the engine to make sure the system was full? Failure to do this can leave a big air bubble in the heater circuit.
I would wait until the engine is cold, and then check:
1) The remote expansion tank should be half full with coolant. Never fill it to the top, and regularly check that it is not empty.
2) The radiator should be full to the top. Check by removing the plastic bung from the top of the radiator. You will find that a spark plug socket fits this bung perfectly. If it is not full, then perhaps you have a leak, or else it is the result of an air lock (see above).
If you get this far and everything looks correct, then I would diagnose a faulty thermostat. These normally fail in the closed position, resulting in the engine red-lining quickly, but the radiator remaining cold. Remove the thermostat, drop it in a pan of boiling water, and look to see if it opens.
