I have a similar problem, running around with just the car - perfect, tried towing caravan up a long steep drag and it started to get hot, then very hot. Had a test carried out at local indy which indicates a very slight head or gasket leak into the water system. This is the second time of overheating, first time blew the radiator. Fitted new radiator, water pump, stat, belt, tensioner and pressure cap so I was pretty surprised when it happened again especially as I had dragged the same trailer as last time up the same hill with no problems.
