[TR] Radiator Caps

[Keith Stewart]

On 2012-03-16, at 8:35 PM, Randall wrote:

>> The TR2 through
>> TR3A engines use a 4lb cap and the TR4 through TR4A engines use a 7 lb
>> cap.
>
>> What is the deciding factor that makes the difference?
>
> Personally, I suspect there was no real reason except they originally
> thought 4 psi was enough, and later decided that 7 psi was better.
>
> But others think it was due to the change in heater design.  The TR2-3B
used
> a circular heater element that internally had wide, flat tubes that weren't
> very strong.  With only a little bit of internal corrosion, they can fail
> from too much pressure and dump scalding coolant onto the occupants.  The
> TR4 & 4A had a more modern, round tube heater core.
>
> AFAIK, early TR4s used the same radiator and thermostat as later TR3s.
They
> did eventually switch to a pellet type thermostat, but I think that wasn't
> until later, maybe 1965.
>
> Certainly there is nothing in the engine itself, as the original engine in
> TS13571L is running quite happily with a 10 psi cap (and no heater).


And so, if the heater in a TR3 (57) was exchanged for that from a Spitfire - I
think Bob Schaller did it to this car when he worked on it in Arizona -
because supposedly that was an upgrade, would that mean a 7 lb cap would be
more appropriate than the 4 lb cap?

Keith R. Stewart
London, Ontario
E-Mail: keithstewartATexeculinkDOTcom