baxkr

Bubbles in the expansion tank sounds like a head gasket. You may find oil in there too. I second the opinion on getting a compression test done - that should be relatively inexpensive and will give you a good starting point. Depending on how badly the engine overheated you may have warped the head in which case you will need to get it machined flat as well. That's starting to get a little pricey (don't ask me how I know 😜 )