Malcom;
        Your theory is possible but I have a more plausible explanation.
It has to do with the speed of the water pump. If you have ever bled the
system you should have noticed how the coolant level in the reservoir
falls with higher RPMs and overflows at idle. I would say you have zero
resistance from the pressure cap.

Good Luck and Drive Safely
Ken Lewis
86 Crewcab,60 356
http://Neksiwel.20m.com/

On Fri, 14 Dec 2001 12:04:34 -0400 Malcolm Stebbins
<MSTEBBIN@MSVU1.MSVU.CA> writes:
> My experience with coolant problems leads me to believe
> that the cap on your coolant reservoir tank is not holding
> pressure.  As long as the van is moving, the coolant is
> not boiling, but at a traffic light the coolant heats up and,
> with no pressure on the cap, the coolant expands/boils
> over into the expansion ..............
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