> Carl, my understanding of 4 cylinder TR radiator caps is:
>
> - TR2 through 3A use 4 psi cap with 1" length.
> - TR4 up to CT9000 approx., with long neck rad\iator (same as TR3), use 7 psi
> cap with 1" length. My car happens to have this radiator, even thought it's a
> later car and should have a "no-neck" radiator. Tonight I measured the
> distance from the top rim of the filler to the lower rim and it's
> exactly 3/4".
Then you've got a 3/4" reach neck, not a 1". This is a common conversion, my
radiator shop offered to do it when I had the radiator repaired. But installing
a 1" reach cap on this neck will result in a disastrous rise in pressure when
the engine warms ... if you're lucky it will only blow out the upper radiator
hose. One of our local club members did this ... his upper hose looked like a
leaky grapefruit !
> The spring in the cap compresses the remaining 1/4".
Nope. If you measure a 1" cap, you'll find that it's slightly longer than 1".
But they compress less then 1/8" when installed, little enough that turning the
cap to the first click removes all spring pressure from the seat.
> I mention the length of the radiator caps above, because they are incorrectly
> listed by many auto parts stores. One or more of the major manufacturers
> incorrectly specify a 3/4" length cap for the long neck radiators on
> early TR4s,
The Stant catalog has this problem ... they don't specify that their 3/4" reach
cap only fits late TR4. According to the representative I spoke to, they do not
currently make a 1" reach cap.
Randall
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