"On my recently purchased A2 (1.4, 75hp, AMF, year 2001), the temperature gauge is acting up: sometimes it goes up to 90° (after about 20 km), then drops back down to 60°, fluctuating at most 1-2 times per trip (60 km). Also, the heating performance seems poor. I suspect a faulty thermostat, but could it be something else?"