Hi Boost Mad,
Get your cooling fan problem sorted out first, then see if you still have a problem? bearing in mind if you have a RS500 style intercooler this does impose higher demands on the cooling system and the fans could be cutting in and out fequentl.

You say whilst driving the car seems to be cooling ok, then when you stop it boils over. Does this happen after you have shut down the engine? or whilst it is on idle? Does it boil over with the header tank cap on or when you remove it? What happens if you start the car from cold give it a few revs then remove the cap? Whilst driving is there any signs of white smoke or excessive steam out of the exhaust?


Just for information, the water returning to the header tank from the turbo will often boil for a time after the engine has been stopped due to it absorbing the high latent heat from the turbo exhaust housing this will occur through natural convection as the heat travels upwards and this will cause you to have air in the header tank, this doesnt mean there is a problem with the cooling system though!

CheeRS, Mike.