I have recently had to remove the oil filter housing / oil cooler unit on my Daughters 2010 Golf tdi 140. It was refitted using a new gasket & stretch bolts tightened to 15 NM, then 1/4 turn. after refilling the cooling system and purging air out I have run the car for approx. 100 miles, temp. is normal and heater ok. However coolant level has fallen and low level warning has come on. There are no signs of water leaking externally and no signs of water in the oil and oil level still normal. Can anyone advise me as to what is going on. Could there still be air in the cooling system?. Any advice would be welcome as I don't want to damage the engine.. Regards, Edward..