May be the 'stat, but I doubt it.
Sorry mate, I think your head gasket may have begun to pressurise the coolant.
You might want to try the 'stat though, as it is very easy and cheap to do. The Haynes books are good at this level.
Check out the radiator/expansion cap first though. It may be something as simple as that not releasing pressure at the correct time.
BTW, The 'stat lives in a housing at the end of the top hose.
But if you are blowing off hoses then my money's on the head gasket.
Keep us posted.
E200 Wagon 1994 108k miles.