Subaru -- overheating

Subaru cannot get the temperature gauge to move during test drives and their tests indicate it is running within normal range – so they don’t know what to change/fix.
It happens to me when

  1. temperature is below 40 degrees.
  2. it happens within 10-20 minutes of driving … regardless of speed.
  3. it happens every day when it’s below 40 degrees – but just since the water pump and thermostat were changed and then the new faulty thermostat was then replaced …
  4. the gauge comes immediately down when I turn the heat and fan on
  5. I try to get it to Subaru when it’s happening, but I’m usually about 25-50 miles away and can’t get it to them when it’s happening
  6. it NEVER happens if the weather is above 50 degrees.