I have always thought this valve is a automatic water diversion valve to allow the engine to heat while the Wabasto is running. It seems to work like a thermostat and open and close according to temperature. I just happen to think that there is no way to make sure it's working properly.
Does anyone know anything about these valves? Not sure If I should replace it since it's 22 years old. Maybe there's a more modern way to divert heated water thru the engine.