T5 Multivan loosing coolant

[steve gibson]

My T5 multivan is loosing coolant . The low coolant warning light come on after about 500 k after topping it up.
It starts and runs really well with seemingly no power loss. It not going into the oil as the oil level is constant and always black.
There is no oil in the coolant. There are no visible leaks. I have had the cooling system pressure tested cold over night and at operating temp for over 3 hrs and then left overnight. No pressure loss.
I have had this vehicle since new and has done 245,000 km. Always had it serviced at the required intervals using the recommended oil.
All theories welcome.

[Umai Naa!!]

What engine is in it?

I'm not sure if the Multivan got the 1.9TDI as an option.

Try a new cap on the expansion tank. They're cheap enough.