First, water pump is OK, and I can find no leaks....
When I head out for work in the morning, the temp gauge climbs into the upper temp range. Most of the time, after about 15-20 minutes of driving, it will drop back to the "normal" position and may or may not go back up. Same thing on the way home later in the day, but temp stays high (about 3/4 of the way up on the gauge).
Coolant level is OK, and the fan is working. Could this be an intermittent thermostat problem? I thought thermostats either work or don't work. Any advice appreciated...thanks!