Trevor,
Sorry, I'm behind in my digests...
The TVS is an anti-overheat device. On later cars, if the coolant
temp becomes excessive, the vacuum line to the ignition retard capsule
will be interrupted, advancing the idle ignition timing to the "static"
value
(10-12 deg BTDC) and promoting cooler running. The function of the switch
is fully described somewhere on my Triumph shelf, I think in one of the
Technical Service Bulletins I have a copy of. I don't know about the last
cars, but on a '74, the following is true:
-If you've bypassed the ignition retard function of your
distributor,
you have no reason to use a TVS. All it does is "turn off" the ignition
retard
function.
-If your car overheats at an engine speed above idle, the TVS
can't help, since the ignition retard functions at idle only.
-If your TVS has failed in the open position, your engine
operation and emissions will be unaffected, but you might overheat
in hot weather at prolonged idle RPM (but then, you will anyway!)
Basically, even if you are subject to emissions inspections,
you don't need a TVS unless you drive in stop and go traffic a lot and your
car has been overheating *at idle*. Get a radiator top hose from an earlier
car (1 piece from thermostat housing to top of radiator).
Best Regards,
Tom Marincic
Own CD3574L-no TVS
Butchered CF23391U-TVS
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