Net Wisdom says that the problem originated with the cap on
the main coolant tank. It is not doing its job of venting into
the overflow tank. Excess pressure built up in the system and
blew out the sensor.

I am going to replace the main tank and cap and the sensor.

I will report back in a couple of weeks with results.

More Questions:

1. Did the excess pressure in the system contribute to headgasket
        leaks?

2. Is anyone else experiencing a problem with the overflow tank
        continually running dry? It seems that the cap lets
        coolant get sucked out of the overflow tank but not
        back in.

3. How can one tell if the quantity of coolant in the system
        is correct and/or that there are no 'air pockets' in
        the system.

Thanks Again,

John-Reed Maffeo '86 Syncro - Glacie
Mesa, Arizona