temperature gauge not working and heat not working properly

[zeerok]

I have a 99 explorer 5.0 and the other day i noticed that the temperature gauge wasnt working, it stays on c. Then the next day i turned on the heater ( i dont use a heater much as i like cold weather) and normally a couple minutes with the heater on all the way i start sweating but i could barely feel it. Coolant levels are good and checked three or four times a week as i have an oil leak needing repaired, also since the problems started i noticed it idling weird. Any help is appriciated.
Thanks in advance

 

[TestPoint]

Sounds like your thermostat is stuck wide open. Better than stuck closed. Best change it as you mpg also just went to about 8 which might be reflected by the different idle due to fowled plugs.