wolfgang wrote:

> I've got an 88 Westy that I've had for about 3 months.
>
>  About 100 miles from home, the red overheat light starts
> blinking.
>
>  the light comes on again.  This time, I notice the
> reservoir is full - the one behind the license plate.  The other
> coolant tank has an air pocket.  So I get a water bottle, slowly
> loosen the cap, let out the pressure and top it off.
>
> This same thing happened once on the way back.  But the needle
> never gets any higher than pointing at the light.

> Could the head gasket be slowly leaking combustion gases into the water
> jacket ?

Wolfgang, you have hit the nail on the head. If the system is operating
correctly, as the coolant expands when it is rising to operating temperature,
coolant will flow from the expansion tank into the overflow tank. That is
proper.

That is happening, which says to me that the expansion cap is operating
correctly. So don't rush out and buy a new cap.  The air bubble suggests that
gases under pressure from some source are getting into the cooling system, and
affecting the resistance in the coolant level sensor probe, causing the
warning light to come on and blink. Obviously if you had to releive the
pressure in the expansion tank to top it off, the expansion cap is working
correctly. So your troubles are elsewhere. And unfortunately, logic says its
head gaskets leaking.

Before spending any great amount of money, take your rig to a garage and have
them do  sniff test on the coolant. They should be able to tell fom the
chemical traces that are picked up if you have combustion seal leakage.

Good luck.

John Rodgers
88 GL Driver