Coolant Boiling in Expansion Tank - Fiesta Zetec 2003

[David Saville]

Around a month ago I noticed a horrible noise after switching the engine off. It was the coolant boiling in the reservoir. The level had dropped and leaked. Couldnt find the leak or any other problems. The oil wasnt mixing (left me thinking it wasn't the head gasket) and the temp gauge was saying normal. I had the thermostat changed(the old one did'nt open when i put it in boiling water suggesting it was faulty) and the temp sensor, and then the expansion tank itself. Unfortunately it didn't solve the problem. The car, although drives ok, makes a whilstling noise and the coolant still boils unless I drive steadily.. I took it to a garage to get a proper diagnosis, They confirmed that there were no leaks and that it wasn't the head gasket. They confirmed that it is most likely to be the water pump. The reason for my first post is a question to anyone who think it could be something else. Ive already paid enough to change the stuff mentioned above. I really dont want to change the water pump(along with the timing belt) if it could be something else

Thanks in advance

David

[Paulkp]

Dd the new expansion tank come with a new pressure cap ? If not try that ?

[EdGasket]

You need to check your fan is running before the coolant starts boiling. See my thread ref. temp sensor resistance:

If the radiator gets nice and hot then chances are the water pump is OK. I found the ECU was expecting a lower resistance from the temp sensor than even a new one was putting out so the fans were never coming on and coolant boiling in the cylinder head.

[Martin-Fiesta-MK6-1.4]

13 hours ago, EdGasket said:

You need to check your fan is running before the coolant starts boiling. See my thread ref. temp sensor resistance:

If the radiator gets nice and hot then chances are the water pump is OK. I found the ECU was expecting a lower resistance from the temp sensor than even a new one was putting out so the fans were never coming on and coolant boiling in the cylinder head.

Same happened with mine, i got an external thermostat fitted with a temperature dial so i can decide at what temperature i want my fan to kick in, installed that instead of a new ECU, cost 100 quid