Hi . This is my first post so apologies if I don't get it right first time ! . Car is a 57 plate Grande Punto 1.3 diesel which we have had for around 3 weeks , All good up to now but a water sloshing noise was traced to low coolant level which took 2 litres to refill to the low mark . 3 days later same thing , then 3 days after that ,etc .I have run the car hard for a while then parked over a cardboard sheet and no leaks anywhere . I replaced the pressure cap today just in case as I couldn't think of any other reason for the loss . I know we have an airlock because the heater blows hot and cold and the temp guage wanders a bit but does not go too high .Car performs well with no apparent power loss , no oil in the water or water in the oil .Any suggestions please ??