My VZ Calais is loosing coolant and requires a top-up of 300-500mL after a trip of only 60-100km. Floor of the garage is wet at the front of the car - under front bumper. Water pump and radiator cap have been replaced twice in the last three months. (Genuine Holden radiator cap used the second time around). At time of replacing radiator cap, the mechanic explained that the cooling system was pressurising when the motor was turned off and the (old) radiator cap was allowing the coolant into the expansion tank, causing the expansion tank to overflow, hence the coolant on the garage floor. Replacing the radiator cap initially solved the problem but only for a two-three weeks. Two separate mechanical repairers have pressure-tested the cooling system and advise that it is all in good order. The car has been to mechanics three times for the same issue. Any advice or suggestions or similar experiences members can offer will be greatly appreciated. Thanks.