remove the thermostat housing again, it it made of plastic. look inside the housing and you will see a piece going across with a tiny hole in it where the stat sits. inspect very closely, you should find that this is broken. ie the tiny hole has pushed right through. this prevents stat from opening causing overheating. obtain new stat housing from vw dealer, refit with new stat, hopefully bobs your uncle.
tomtech ! i did notice a through small hole in the mating hose portion of thermostat housing should this hole be blind ! or is thermostat housing that suspect ? great help thanks.
the small hole on the inside of the stat housing should be blind. the spindle of the stat sits in that hole. if the hole has pushed right thru, that is your problem. put a cocktail stick or similar into the hole. if it goes right thru theres your answer. its a common fault on polos.