>>>Also, the coolant light on my 84 Vanagon blinks for a while when I first start it and sometime will go off after driving for a while. The sensor in >>>the expansion tank is new (twice 'cuz I thought the first one was bad) and stays full of coolant. How are these supposed to behave?

Mark, 

Check the mixture of your antifreeze, it should be 50:50. The other possibilities are poor grounds or a weak battery. The sensor in the expansion tank works by running a current through the antifreeze in the tank, if the antifreeze is low current will not flow and the light will blink. The light will also blink because of the problems listed above. 

My coolant light often blinked for a minute or two after start up, but after I cleaned up all the grounds the blinking stopped.

The light should blink when the engine is first started (so you know it works) but only for a few seconds. 

George 

'85 Westfalia