Quote Originally Posted by MuteMarmoset View Post
If this were the issue, would it not overheat every time the car was driven? … .
You're saying it's overheating, but I don't see any mention of actual coolant temps here (either measured or from OBD), and I suspect the shops are not finding a problem because the engine is actually not overheating. In prior forum threads on this issue, IIRC there was no mention of overheating, just a reservoir cap that was no longer holding pressure.