Hi,
I recall 'recovery' caps, coming in around the late '70s.
Do you have one? To find out, remove the cap (cold, please) and examine it.
You'll see, from the top down...
1. the bit you grab to undo the cap.
2. A concave metal flange (or not) with a rubber seal (or not)-they vary.
3. A stem, with the spring around it.
4. The lower seal unit, which sits against the flange in the rad. neck.
Recover caps have a lightly sprung, circular valve (with rubber seal on the
bottom face of the lower seal unit. This valve can be lifted off its seating
with little effort.
How it works...
Under pressure, both the bottom sealing unit and the overflow seal are
closed.
When the pressure goes higher, the BSU lifts off its flange in the rad.
neck and overflows into bottle, onto road or whatever. (Scenario:when an
overfull rad heat soaks when the engine is shut off hot)
When the engine cools, a vacuum is formed; the overflow valve is sucked off
its seat and water is drawn back in from the overflow bottle.
These caps seem to be pretty much universal now. They work on systems with
no bottle, because the vacuum has nothing to recover. In my experience, a
pressurised bottle is not an overflow but is expansion space; where the rad
has a cap. it's usually plain (no spring or BSU).
BTW, I fill my GT's rad. to just above the coolant tubes-no higher-and it
neither overheats nor drops water.
Cheers,
Dave Hill
Can I Telework for you? See what I do, at...
http://www.angelfire.com/biz4/davtel/index.html
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----- Original Message -----
From: <Gonaj@aol.com>
To: <Ajhsys@aol.com>; <ATWEDITOR@aol.com>
Cc: <mgs@autox.team.net>
Sent: Thursday, April 06, 2000 9:35 AM
Subject: Re: coolent recovery
> All of the caps that I recall have a spring between the top of the cap and
> the seal which mates with a flange inside of the filler opening. This
flange
> (seal) is below the overflow and prevents coolant overflow until the
pressure
> of the system, as calculated for temp., exceeds it's set point.
>
> In order for the system to be bi-directional the spring must be a
bimetallic
> so that it will operate like a thermostat. All systems must be
> bi-directional regardless of weather they were originally equipped with an
> overflow tank or not. If they were not bi-directional there could be
enough
> vacuum created as to crush the thin walls of the radiator tubing.
>
> Now I will grant you that I am sitting in isolation at 3:30 AM theorizing
as
> to the physics of what is happening but I am confident as to my
conclusion.
> FWIW
>
> George
>
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