I have inherited a 1993 Ford Sierra from a cousin. He bought car new in 1993 and has only done 50,000 miles. Car kept in heated garage and serviced every year even though it has covered less than 2000 miles a year for last 10 years.

I have an unexplained problem which previous owner also had. I can check water every day for 3 weeks without seeing any water loss, then suddenly will find expansion tank empty. I recently drove to/from my holiday cottage in Co. Durham (round trip 600 miles) without using a drop of water. On return used car for perhaps 10 miles a day, checked water every day and on third day all gone.

Have had system pressure checked. New radiator was fitted last year (2000 miles ago). I have had electric fan and sensor fitted.

There is no evidence of water in oil, completely sludge free. No evidence of water on ground. No evidence of overheating. In 4 months it has happened perhaps 6 times, and I can be certain as I check the water evry time I use the car.

Does anybody have any suggestions as to how this can be happening.

Incidentally car drives like a dream, feels/sounds like a 2 year old car. I have in the past had a collection of classic cars including Bentley, Daimler, Alvis all of which I maintained myself so am a reasonable home mechanic, frankly this one has got me beat!