I own a Fiesta Zetec 1.25, T reg. I drive for about 4~5 miles and the heater gauges on the dash board goes up to the red mark. When I go around 4k rev's the temperature gauge goes back to the middle point. I then drive for a while and the temperature gauge goes back upto the red mark. The temperature gauge again comes back down once I approach 4k rev's. The fan operates. What can be the problem? Thanks.
This could be the heater control valve, or thermostat. try to bypass the heater valve first then recheck