temperature light on 2002 Ford Taurus

The temperature light goes from middle to hot and back and forth continually. I had to have the radiator hose replaced and I have put 2 gallons of anti-freeze in the resevoir. What would cause the constant moving back and forth of the needle?

Asked by for the 2002 Ford Taurus
If your thermostat is old it could be malfunctioning. If your thermostat has more than 60,000 miles, it is in need of replacement. Then re-check and get back to me if you need more assistance.
Turns out the mechanic at Kwik Kar in Lindale TX did not install the radiator hose properly...missing clamps and lose connections and all the anti-freeze and water was leaking out slowly.
2 answers 2 comments
If your temp is fluctuating that much, it could be the thermostat, but it seems that thermostats either get stuck open, which would make the temp run cooler because the coolant is circulating constantly. If it is stuck shut, it will not let the hot coolant out and the temp would rise and stay high. It sounds to me that it is low on coolant, and that will make the needle rise and fall rapidly. Change the thermostat and check and fill coolant level, and let it run with the heater on with the reservoir cap off, and that will help purge any air out of the system. Let the thermostat open and close for 5 or 10 minutes before topping off coolant and replacing the cap.
Turns out the mechanic at Kwik Kar in Lindale TX did not install the radiator hose properly...missing clamps and lose connections and all the anti-freeze and water was leaking out slowly.