In a message dated 3/31/2001 5:21:55 PM Pacific Standard Time, JKrevnov
writes:

<< Why do you say that the coolant system is being pressurized?  Have you
tested it with a pressure gauge or is the coolant filling the coolant
reservoir and coming out of the vent holes on top?  If so, it may be merely a
defective pressure cap on the pressure tank.   >>

Rich,

Very good point! The same analysis led me to replace the expansion tank cap
twice before I became more sophisticated about the failure mode.

Operationally, the "pressurization" is evidenced by the complete filling of
the filler tank and the subsequent overpressurization of the expansion tank,
driving the fluid level down below the sensor warning level.

In the shop we were able to note the pressurization through attachment of the
pressure guage to the expansion tank.

Tom