Hi Carl and all,
First of all, let me correct one thing. I said in my earlier response that
"overflow tanks" were a "one way" system. As some others have pointed out,
that's not entirely true. It's a one way system only while the car is running
and
the cooling system is under pressure. But, once the car is shut off and the
system cools down, with the right radiator cap, coolant will return to the
radiator. Another response correctly pointed out that the "right cap" has a low
pressure valve, opened by the vacuum created when the radiator cools, allowing
coolant to return.
True "header" tanks are a two way system all the time: catching overflow,
eliminating air from the radiator/engine and returning coolant to the radiator
as
needed, while driving.
Still, the mounting of an overflow tank is less critical than a true header
tank. The former is usually below the level of the top of the radiator. The
latter needs to be at a level slightly higher than the top of the radiator,
which
might mean installing it pretty far from the radiator in our cars.
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".
The
spring in the cap compresses the remaining 1/4".
- TR4 after CT9000 approx. and TR4A, all with "no-neck" radiators, use 7 psi
cap, 3/4" length.
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,
possibly TR2 & 3 as well. I had an email exchange with John Swauger at The
Roadster Factory this week and even they are having trouble getting the
manufacturer to supply the right item. They just got a shipment of incorrectly
sized 7
psi caps. Using a 3/4" cap on a car needing 1" is a good way to cause heating
problems and I've currently got the wrong cap on my car (which isn't going
anywhere under it's own power for a while, anyway).
Sorry for any confusion due to my earlier posting. I hope this clarifies.
Alan Myers
San Jose, Calif.
AMfoto1@aol.com
http://hometown.aol.com/amfoto1/amfoto1.htm
Date: Sun, 23 Jan 2005 19:14:51 EST
From: CarlSereda@aol.com
Subject: Re: Two TR3A radiator questions
Hi Alan,
Can't TR4s easily be made to draw radiator coolant back to the radiator from
the catch tank when engine cools off - rather than the bottle simply being
used as an overflow catcher?
I bought a NOS Stanpart TR4 spec'd radiator cap that has additional gasket to
seal the top of neck (rather than just metal-to-metal neck connection) as
well as the rubber seal for the inner filler hole plus a smaller built in
'return' valve.
I assumed I could have a good "closed" 'back-and-forth' system..
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