There is no buzzer on the coolant. The buzzer is on your oil pressure. This can be caused by wrong oil (vanagons should use 20w50 (or 15w50) or straight 30w oil so as to main proper oil pressure at operating temperatures (lighter oils in areas that suffer extreme cold temperatures, but then you should also reduce top speed)

The other reason the oil pressure buzzer will go off, is if you are operating with too little oil. The buzzer means. STOP IMMEDIATELY. 

Since you have an intermittent issue, this is either, wrong oil, or oil pressure switch is bad.

On Nov 4, 2014, at 3:34 PM, Dennis Jowell <dennisjowell@GMAIL.COM> wrote:

> I am trying to understand the warning light on the temperature gauge of my 1988 Westy.
> Going off the interstate the light and buzzer goes on for a second. If I accelerate slightly the light and buzzer goes off. Is this telling me that I am low in coolant? Coolant temperature is mid range all the time. Or is it and oil pressure issue? Read my Bentley and owners manual still no explanation.
> 
> Dennis Jowell
> Scotch Hollow Farm
> Newbury Vermont