gpan951

I have the same problem-I top up the expansion tank about every 10 days with a liter of water....no leaks evident, no milkshake nor mixing in any other fluids.
I did suspect the expansion tank cap, so I attached a container to the overflow line and drove around for a bit but it was bone dry upon inspection (the container).
I do think that it's a light leak and it evaporates on a hot engine part, hence no trace.