Cooling fans stay on

After doing the intake gaskets and thermostat on a '98 Malibu with 3.1 we noticed that the fans come on at the right temperature (224 deg.). But what's weird is that they will remain on seemingly forever even after temperatures drop below 200. If you turn the car off and immediately restart it the fans are off. What's weirder is that while the fans are on if you drive about 50 feet the fans shut off. I don't understand why it makes a difference if you move the car or not. If the fans are able to cool the car down to below 200 while it's not moving why does moving it get them to shut off. With a scanner attached to the computer I can see that when the car is moved the fans will shut off by 206 degrees yet when the car is standing still the fans will remain on even if the temp drops to 199. I'm thoroughly confused. Anyone have any ideas?