While answering another post a couple of other points popped up in my mind:
--The engine case must NOT be painted!! There has been much debate on this on VW forums around the world and the final verdict was that it IS a cause of overheating.
Also the engine shields must only be painted black and not other colors.
--The engine compartment rubber seal which goes all around must be in good condition. This can only be installed with the engine out of the car.