Every now and then, at traffic lights, the heater goes cold and the radiator fan comes on soon afterwards. The cooland is topped up as much as it'll go.

I understand the topping up the coolant procedure is a case of letting it idle until the fan comes on, letting it cool down, and then topping it up, repeating until it's topped up. I've done this, but there must be some air still trapped in it... unless it's something else. Any ideas?

 

I should also have mentioned that it's fine when you're driving along. Maybe it's the water pump?

 

Possible you have a leak, keep checking the level in the header tank (front left top of engine) not the one by the passenger headlight as that is often empty.

When you are driving the revs will be higher and therefore the water pump will pump faster, over coming the air lock..

I have removed my radiator a couple of times and refilled via the header tank and even after the level needs topping up, but never had a problem with the heater etc..

I very much doubt there would be a problem with the water pump.

JGM

 

They're both full. Weird isn't it?

 

try filling the big top hose on the radiator by taking one end off and filling it manually with coolent?

worked for me

 

You will probably already know this but just in case - make sure you have the heater set to full temp in the car when you are running the engine up to temp