Gauge reads over heating, but radiator is not hot

I have a 2001 chevy cavalier (2.2) with 145000 miles. It's been a very mechanically reliable car and I have taken care of it. In the last week the temp gauge started to read hot but came down when traveling at higher speeds. Discovered that the fan was not turning on because the cooling fan sender was bad, so we replaced that. The car continued to read high on the gauge so we also replaced the thermostat. The gauge continues to read high, although the car drives fine, and the radiator is not hot (you can leave your hand on it). Today there coolant overflow under car after a short (2 mi drive). There's never been any steam or losing power. Is the sender for the fan the same as the sender for the gauge. Could the gauge be bad. Any ideas?

Janick:banghead:

Sounds like you have an air bubbble somewhere, not allowing the coolant to flow properly. Do you have heat?

Homerr