Hi, I am having a similar issue in my 95 Vienta V6. I am losing coolant somewhere, needing to top up the coolant bottle weekly, up to 1 litre depending on how much I use the car. No visible leaks or puddles under car and no milky oil. The car is running fine and is not overheating. Have had the filler neck on the engine replaced as it was slightly corroded and cap replaced but no change. Also had it pressure tested by mechanic and was advised there was no problem. I am thinking of taking it to a radiator specialist for another test. Anyone got any ideas on where to go from here. Water pump?? Trebor1980, did you reslove your issue?