300tdi head gasket failure? Huge coolant loss

I cant see any evidence of a leak there unless its so slight that it evaporates before reaching te ground, but when its been sitting in a spot for a while there are no leaks underneath the car at all.

I must try and get the radiator and bottom hoses out and flushed.

I think I may have found the source of my problem.

When going through each of the hoses to check for sediment etc I removed the expansion tank to flush it out too. Once removed I heard a rattle from inside. It was a pebble!!!!!

So I think it had been blocking the return side of the cooling circuit when it sat covering the outlet. Hot water from the thermostat housing overflow would have been coming in at a quicker rate than the return side, filling up the tank to overflowing.

I need to get a new water pump gasket and rebuild everything tomorrow to check my theory.