I have a 2001 Audi A6 1.9 TDI 130 SE. Its given me 247,000 miles of trouble-free motoring and for the last 147,000 miles has been maintained by a local Bosch garage. The radiator was recently replaced (due to a small leak) along with the water pump as part of a cam belt change at 240,000miles. A new fan was also fitted for the air conditioning. Since then, the car repeatedly loses coolant (approx one litre for 100 miles of motorway driving). The rate of coolant is much less when driven at lower speeds. The car has been pressure tested three times with no leak located. Also, although using a litre of coolant the engine temperature gauge doesn't increase. My theory is that the fan is faulty and doesn't cut in (the fan also seems to be vibrating). I understand the second fan cuts in as the engine gets hotter. Could a failure of the fan cause this level of coolant loss? Is there any link between the coolant loss and the operation of the air conditioning compressor?