I have an A4 1.9 TDI 130 Bhp 2004 that's leaking engine coolant badly. I have tried everything but cannot find the source of the leak. The harder I drive, the faster the coolant leaks. For example Drive easy for 50 miles = 1/4 litre coolant, Drive hard for 50 miles = 1 and 1/2 litres. Basically it emptys itself when driving hard. I've already replaced reservoir bottle and cap, water pump, thermostat and seal, plastic seal connection at rear of block, i've tried bypassing the heater rad, changed all hoses and clips. There is no sign of a coolant leak anywhere under the bonnet. I'ts been like this now for almost a year. It doesn't overheat as long as you keep it topped up as soon as the coolant low light comes on in the dash ( I'm running on water with the last while, the coolant was getting too expensive). The engine oil looks normal, recently changed. There is no sign of water coming from the exhaust. I'm thinking the head or head Gasket but don't realluy want to touch it until i'm positive that this will fix the problem. Any Thoughts?????