I have a 1994 MPV which over heats after 30 minutes of driving. checked thermo; flushed system; evacuated air
sounds like you might have a heater core problem,not allowing the water to flow through the engine to cool it and by being blocked the hot water is not passing through enough to produce a hot surface to heat the car.
Search Mazda MPV Questions
Are you a UK consumer? CarGurus now has a discussion forum in the UK.
Mazda MPV Experts