I've replaced the cap with a new one, with all the parts in place. It
still runs water out of the overflow tube, so I think we may have
another issue.
I measured the distance from the top sealing seat to the lower sealing
seat - approx. 0.750" - and the distance on the new cap from the upper
seal to the lower seal - approx. 0.800". That difference (0.050")
doesn't seem like enough of a difference to me.
Any ideas as to how much the spring should be compressed to hold the
pressure?
Scott B.
-----Original Message-----
From: Tony Drews [mailto:tony@tonydrews.com]
Sent: Wednesday, June 03, 2009 9:04 AM
To: Barr, Scott; fot@autox.team.net
Subject: Re: [Fot] Radiator Caps
Your assessment is correct. The lower seal and the little button in
the middle are what hold all of the cooling system pressure. The 2nd
thing to look at is how deep the well that the rad cap fits into
is. Older british cars seem to have a deeper well than is common
now, causing the lower part of the radiator cap to not seal against
anything causing zero pressure in the cooling system. Someone
(probably Moss or TRF) sells the caps with the longer actuating
mechanism. I've seen that problem on 2 or 3 different cars with
inexplicable cooling problems. The first one took a LONG time to
diagnose, but after I was aware of that potential issue the others I
was LOOKING for that problem.
If you have a rad cap with an overflow in the header tank, you could
plug up the overflow from the radiator. I think you should have only
one pressure relief / overflow in the cooling system.
- Tony
At 07:41 AM 6/3/2009, Barr, Scott wrote:
>Tony's recent comment about his radiator cap got me thinking about the
>tendency of my 1296 Spitfire motor to fry cylinder #4. While at the
>track a couple of weekends ago, I pulled the overflow tube out of the
>tank and let it dangle, poured water in the header tank and watched it
>run out of the overflow tube - with the radiator cap ON.
>
>I'm assuming it's not supposed to do that. (At this point, I'm
>reminding myself that there is no learning without humility...)
>
>I looked at the radiator cap and noticed that it does not have a lower
>seal and that the vacuum valve is not there. I had always ass-u-me-d
>that was the way it was made. But now that I'm thinking about it, it
>appears to me that it would allow water from the engine to flow through
>the hole where the vacuum valve usually is and out the overflow tube
>into the overflow tank, holding no pressure in the cooling system at
>all.
>
>I've replaced it with a new radiator cap, having both seals in
>place....and water still runs through - but that's a second question...
>
>Scott
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