In a message dated 1/13/2007 1:58:09 AM Central Standard Time,
areich@telus.net writes:
> With all this talk about radiators and thermostats, etc I have a
> question about a rubber ring that is in the hole at the bottom of the
> radiator cap housing.
> I have asked a number of other TR3 guys and nobody seems to know what or
> why it is. One person suggested it would not allow the pressure cap to
> function properly. I can take it out easily and it does not appear to be
> home-made
>
The radiator cap includes a couple of pressure regulating features to keep
the cooling system pressure within a safe range. One is a pressure relief
valve. This rubber ring, and the steel disk supporting it, will seal up
against
the "seat" in the radiator throat. This disk is spring loaded and will form a
a
seal to keep the system pressurized. But as the cooling system pressure
increases past a point the force applied to this disk and rubber ring will
overcome the spring tension and the ring will lift and bleed off a bit of
pressure
keeping the system pressure at the max allowed value.
An important thing to note is that the throat in the TR3 radiator is deeper
than what is typical in modern cars and if you fit a typical cap the rubber
ring will not even reach the seat and cooling system pressure will remain at
zero. Since water boils at a lower temperature at lower pressures this can
lead
to boil over even though the temp gauge reading will not show an overheat
condition. This is especially true when driving at high altitudes. Therefore
it
is important to fit a cap intended for a TR3 onto a TR3 radiator.
The other pressure regulating feature is a vacuum relief that will bleed
pressure back in when the engine cools down. Drawing a vacuum can cause the
hoses
to collapse.
Dave
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