>>
>>
>>>
>>Failure of this second function would cause your symptoms.  In other words, 
>>some coolant is normally carried out to the reservoir during normal running. 
>> When the engine cools, instead of coolant being recovered through the 
>>valve, the negative pressure is satisfied by the hoses partially collapsing, 
>>etc..  The next run cycle dumps a little more coolant, and so on.
>>
>>So, I would check the valve.
>>
>>Mike
>>

I just found your posting so this reply is kind of late. For some unknown
reason replacement of this cap (valve) did not fix my cooling system problem
for my 83 westy. The coolant continued to flow out to the reserve tank. 
Combustion gas still remained inside the pressure tank. I had refilled it
many times. Cap replaced once and the same symptom appears again and again.
Got to get rid of the root cause - leaking head gasket.

David Kao
dkao@eng.sun.com
83 westy, 84 vanagon