Since last summer, car's needed the occasional top up - maybe an inch in the expansion tank every three/four weeks. Rather stupidly I was topping it up with just water. The car has always driven perfectly and never had any problems, driving an hour each way to work and back etc. Two weeks ago on an extremely icy morning, half way to work after half an hour of driving the temp needle went right up into the red all of a sudden (it always normally moves up to the centre and stays there), so I stopped immediately and switched it off. I waited 10 mins and carefully took the expansion cap off and it all came spewing out. Filled up with water (about 1L had come out) and drove home same distance, no problems at all. Had a look last weekend and could see nothing wrong. Engine warmed up ok, thermostat opened etc. Couldn't get it hot enough for fans to come on - though they do come on with AC on. Can only guess it was a one-off stuck thermostat. Drained some of the coolant and replaced with new at 50/50. Car runs fine again, temp gauge always dead centre etc, and didn't seem to be any coolant loss for over a week (still driving 350 miles+ a week), though usually notice a bubbling sound after switching off warm engine. Yesterday however, coolant level had dropped again, and needed about another 750ml to top up. And again today it needed another 1/4L to top up! No obvious sign of leak (though ground is wet anyway) and no water/scale marks visible on engine. Mentioned slight water loss to ford at last service (Nov) and they couldn't see anything. Could it be that there was still a lot of air in the system which has slowly found its way to the expansion tank? (therefore looking like water loss) if there's still more air in there, how do I get it out? ...or am I barking up the wrong tree?