bubbles in expansion tank?

[Dave W]

Depending on the size of the leak in the cooling system you could possibly see white smoke in the exhaust.
Probably the best route is a compression or leak down test. It could possibly be a crack in the block or head. You could try re-troquing the engine head gasket. But since you have to pull the cams, it is almost the same amount of work as installing a new haed gasket. If do re-troque, only loosen one head bolt at a time. Using a center to out board sequence, using a troque wrench. Dave W