It could be a water leak. Check the spherical water bottle at the top left of the engine compartment. If the levels down top up.If it goes down again you may have a leak.If its leaking it could be from one of the pipes or it could be a head gasket problem.A compression test can point out where the leak is.First though have you felt the radiator?It should be warm after a journey. If its cold it could well be blocked. I,ve had this problem and needed a new radiator.
Dave Towers
August 2007