>>      My '84 Vanagon camper has this problem where every 30,000
>>miles or so the head gaskets begin to leak, causing gas buildup in
>>the water  cooling system.  This first appears as a rising coolant
>>level in the overflow tank next to the oil dipstick. Next the
>>dashboard heater quits because it fills with gas.  Finally (about
>>2K miles later) the leaking gas literally blows coolant out of most
>>of the cooling system and the temperature sensor begins to signal
>>imminent meltdown!
>
>In my '85, I had an experience last week of coolant overflowing the 
>overflow tank. Level rose. meltdown was signalled by temp. sensor. They 
>drained and replaced the coolant and could find no other "cause". It now 
>runs fine and temp is back to normal.
>
>Strange.
>
>James Cook

When mine started having the same problem after its headgasket replacement
at a cost of $900 in 1987, both my VW shop and local VW dealer believed the
headgasket would have had another meltdown and cracked gasket AGAIN. I refused to
believe it and pay another $900 every 30~40K miles. Since 1990, I have been flushing
the whole cooling system every fall. From then on, my water-boxer with "supposedly
cracked headgasket" has added another 70k miles. Well, when it crowls up the Russian
Hill in San Francisco, its temperature does go up a notch or even overshot the
temperature warning light. But, by moving the temperature leveler right-and-
left, the temperature comes down easily. 

It is a fact that these early VW's ('83-'87) water cooling system, due to its high
elevation radiator and very long hoses, is VERY easy to have air accumulated in it. After
a while, air will start cooking your cooling system and cause major damage. So, the 
periodical flush becomes a very important preventive maintenance.

Regards,
James