89-91 100/200Q Heater Valves

[David Ritter <dritter@mich.com>]

Hello,
Seems like we've been hearing a bit more than usual about the failure
of these pesky little heater valves. I don't really know all that much 
about the valve, but have a theory or two.
On most cars I have owned, the heater valve doesn't move at all
during the summer months. It is closed and stays that way.
Now, the guys at "team door handle" had a better idea. They made it
vacuum operated, like the rest of that wonderful climate control
system. The trouble starts with any loss of vacuum to the valve. The
failure mode is full on, more hot water into the heater core.
The valve must cycle every time the car is started or shutdown, as the 
spring overpowers whatever vacuum is left over when the engine is shut 
off. My theory is, that the excessive heat this summer combined with old
plastic valves, has led to the increase in failures. The cycling of
the old plastic parts at high temps, can't be very good for them.
If these valves were closed at all times in the summer and not cycled
continuously, I'll bet they would last longer.

I changed mine this morning, it hadn't started leaking... yet.

David