[v12-engine] Repairing leaky thermostatic switch

Problem: Stopping a leaky V12 Thermostatic Fan
After changing the waterpump and flushing the
cooling system in my car (air-conditioned 1976
EFI SII XJ12C), a small leak occurred at the
rubber push-in-type bushing surrounding the
switch after the car was warmed up for the first
time. (Parenthetically, the leak only allowed the
loss of
about 1 cup of coolant, and seemed to stop after
the switch was pushed a fraction of an inch back
into the
rubber bushing.) I plan to fix the leak. My
first option is to replace the rubber bushing and
use the existing
switch (which works fine). Does anyone know if
the switch itself must be replaced too, to
guarantee a
seal? If I am doing that much however I�d like to
get rid of the rubber push-fit sealing arrangement
modify it so it won�t �pop out� under pressure.
Do some later V12 engines use a screw-in type
thermostatic fan switch? And is that switch
mounted in the cast alloy lower radiator hose
If that is true, can that later elbow
(incorporating a screw-in type thermostatic fan
switch) be
installed in my car?
Does anyone out there know the early and late
parts well enough to know 1) if there is
elbow interchangeability? 2) If it exists, does
the screw-type thermostatic switch have the same
set points
as my old type switch? 3) Do any of you have
experience with such an upgrade? 4) If no to all
of the
above, what special precautions for a leak-free
seal should I observe if using the earlier model
Thanks for any advice you all can offer.

Jim Taylor, Palo Alto California
1976 XJ12C
1970 XJ

Jim Taylor asks a few questions about a leaky “Otter” switch
(thermostatic fan switch).

Most importantly Jim, the sealing ring must be replaced anytime
the switch is removed. The switch you can reuse. The sealing
rings are strictly single use and are only about $3 each. I used
one tonight. Personally, I like them. They seem to be very reliable
and are certainly easy to use. Just put in position then push the
switch home. Maybe that’s why I like them ; )
As to your other questions, Kirby address at least some of them in his
Steve Chatman