My 99 Passat 1.9TDI is mysteriously losing coolant. I took into the dealer who pressure tested the system and said there were no obvious leaks. He suggested I might have a dodgy water bottle or cap, but I think this is a long shot. Some days I can drive 100miles plus and when I check the bottle the water has dropped maybe an inch or two. Other days I only need to drive 30 miles or less before the computer tells me to stop and add water. I then need to put in nearly 2 litres. I do not notice any water dripping out from under the car when it's left overnight, it only leaks when it's running. Anyone any ideas what this could be?

The turbo is coolant and oil cooled. If one of the coolant seals blew out then the car would be burning it, if there is any amounts of white smoke from the exhaust than its burning it.

Thanks for the tip.

I took the car into my VW dealer in Fuengirola, Spain. They kept it for 10 DAYS!! doing tests. In the end they had to take the head off and replace some sort of ring inside the engine and replace the head gasket. I also got them to change the computer into English and fit an air filter which the other garage in Gibraltar failed to do on the service. Whilst in I had the belt changed as well for good measure. The whole thing cost me 1200 euros, which was a bit of a shocker, they did give the paint a polish up though. I've been driving it now for three days and so far so good. No coolant loss!!