My '85 Westy isn't a daily driver anymore and sometimes I go weeks without
using it.  Last night, I pulled out of the garage and within 1 mile the high
temp light was flashing and the temp needle shot up.  This has happened
twice in two years.  I shut off the engine and waited 30 seconds, then
restarted it and all was well.  I drove 15 miles or so, played my hockey
game and came home with no other problem.  What's happening?  Bad
thermostat?  Do I have air in the system?  How did it get there while parked
in my garage?

Thanks,
Kyle