1989 westy , stock 2100 with 28k miles on it.  Well I decided to drive to New Orleans from Dallas .  About 150 miles out from NO my temp light starts flashing.  I stop pull over .  Check the water in pressure tank, full up no air.  the reservoir  is higher than when I left??  The engine does not feel or Smell hot.   I start back out and notice the needle is going  over the light instead of under as it usually does on a 70 deg day.  I put on the front heater and the needle goes down to the bottom of the flashing red light.  I can live with a little warmth and the windows open.  Stop for gas .  Open the back hatch and uncover the engine again to see how things are.  Still the same, coolant wise.  engine still running cool.  I notice if I shut it off right away it stays cool.  If I let it run at a stop it creaps up in the heat to the top of the light.  I don't wait for it to go further.   Either shut it off or get going.   I get into NO and shut it down to check again / after the battery light comes on.   Maybe this is when I should buy a LOTTERY ticket as I have used up all my BAD luck..  Levels still full pressure tank , high as in up to filler cap in filling reservoir, seems cool.   I start the engine and the temp light is out after normal 5 or 6 flickers.  Drove 30 miles and all seems ok.   Any suggerstions as to what happened ?   Why was the light flashing?   I have read it is due to over heat or air buble??   Temp was ok.   Where is temp sensor at?  pressure tank??  Radiator??    Oh I changed the alternator in the NAPA parking lot, GREAT folks.  
Now I have to make it home.......
Tom 
Coppell, Tx.