Mitsubishi Repair: cooling/heating 1997 mitsubishi eclipse, coolant temp, engine coolant

Question
hope you can help .i have a 2.0 motor sitting at idle it starts to heat up to normal temp.driving down road it seem to get colder gauge goes to cold and almost no heat . ps fans only come on when i put on ac or go to defrost .took motor out of another car heat was good  

Answer
Scott,
Your thermostat may be stuck open, allowing coolant to constantly flow across your radiator without it being regulated properly. This could also be caused by a faulty engine coolant temp sensor or a coolant mixture with a ratio of water over 80%.  A good start would be to have those items checked.
Good luck!