So I have been having trouble with my explorer going through thermostats, one every year. Well Monday I noticed my temperature gauge going from normal to cold when ever I let off the gas and then start to go again. So I replaced the thermostat yesterday (I use motorcraft thermostats every time) and I am still having the the temperature gauge go from normal to cold. I can also tell that there is a change in the heat coming from the vents when it drops to cold so I ruled out that it was a gauge promblem.There has to be another promblem but I can't figure it out any help would be appreciated.

possibly an air bubble

Are you positive that you put the thermostat in correctly? Its possible to put it in backwards, with the result being that it will stay open all of the time. Spring side should go towards the engine.

I did not put it in. My father inlaw is the head mechanic at the local ford dealership. He said we would try to troubleshoot it more this weekened but I thought I would see if anybody else might have had this promblem with there's and save me some time this weekened.