Hi all. Octavia 110 tdi, lost water a couple of times from the expansion tank:confused: not sure if the presure cap is falty or the head gaskets gone:Yikes:. The water in the tank has a black somthing on the top, but not oily more of a powdery type of thing. With the cap off if you rev it a bit the water will rise and a few bubbles come up:eek: not sure if its the gasket or trapped air. If you put the cap on the hoses don't pressurise like you would expect if it was the gasket (unless very slight leak).

If you push it on the motorway after a while the temp will rise drop and lose water out of tank only.

Any ideas anyone.

Cheers

replace the presure cap it is the easy and cheap way to start troubleshoting.

Any white gunk on the oil filler cap?

or the dipstick?

Oil is fine, could the black floaty stuff in the water be from the exhaust gas, like i said its not oil but i suppose it could be carbon deposits, if you run it to temp with cap off after a while when you rev it will rise and come out the tank, with the cap on it will come out the tank if you drive it hard.

If it is the head gasket are they much of a pain to do.

When was the waterpump last done? They have a habit of going Pete Tong if not replaced at required intervals.

Have not replaced waterpump but would it not overheat if the pump was faulty? also took it steady today (not above 2500 rpm on motorway & round town) and it has'nt lost any water and the black stuff has gone and the header tank is clean inside:confused:

Sounds a bit like the pressure cap to me (at least as a first stop).