What makes the secondary coolent tank overflow on a 1984 Westy?  It
only does it after cruising on the hwy and then stopping. The heat
indicator rises at idol, but drops when the fan turns on.   PLEASEEEE
DON'T 	Head gaskets.   
	Sometimes the light behind the heat gauge comes on.  If I tap the gas
pedal it goes off. Once or twice upon starting the van the light came on
and the needle pegged out. I know it was not over heating because it had
only been running for a few seconds.