I have a 2000 Ford Explorer XLS. Ever since I have owned the car, it was taken a while to warm up. Never thought much of that. Now, the temperature fluctuates a lot. Also, after about twenty minutes of driving, my heater will stop working and the temperature gauge goes to about 5/8 and will come back down to 3/8 and continue until I stop. Only once has it heated all the way too hot but came back down once I pulled over. I changed to thermostat about a month and a half ago, but don't know what it could be. Any suggestions?

 

If it wasn't too much trouble change the thermostat again. You might try getting it from a Ford dealer so you can be sure its the right rating. We usually try the simple things first if that doesn't solve the problem you may need to check out other causes.