Jim,
 
> My coolant temperature indicators are intermittently screwed up.

 <snipped some more symptoms described>

Your symptoms sound like what I was experiencing when there was a 
small leak in the coolant system.

When there is a small leak, air can get into the coolant system. 
The air in the system can cause the temp gauge to read high. 

My leak was where one of the rubber coolant hoses is held on by 
the orginal "spring pressure" hose clamps. I replaced the clamp
with the "screw" type hose clamp, bled the system, and the problem
never appeared again.

Drew Jenkins  86 Syncro
djenkins@focboro.com