Date: Fri, 27 Aug 2010 18:51:49 -0700
Reply-To: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Scott Daniel - Turbovans <scottdaniel@TURBOVANS.COM>
Subject: Re: coolant system pressure
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reply-type=original
re
"cooling system reaches approximately 15 PSI on every
drive that is sufficiently long to heat the engine and coolant to full
operating temperature. If it were not so, the overflow tank (behind
license plate) would be unnecessary."
this isn't quite true.
before cooling systems had overflow bottles the 'expansion and contraction
of the coolant due to heat' was accommodated by having an air space at the
top of the radiator ..
look at some of metal 60's radiator ..there is a large 'tank' on top of the
radiator.
You can't fill those to the tippy top and expect it to still be full to the
very top after the next cool down cycle.
When you fill that kind of cooling system to the very top, it will just push
out extra coolant as the coolant as it expands due to heat, and after the
next cool down there will be an air space at the top of the rad, in that
tank, and it's working like it should.
Move forward a decade or so ...the front of cars are lower ...the expansion
tank isn't on top of the radiator anymore ...
instead there is an overflow bottle, and the pressure cap has a 'recovery
valve in it' ..
so radiator is full to the top,
coolant expands and is pushed out to the overflow.
when things cool down, the extra coolant in the overflow bottle is sucked
back into the system via the little 'recovery' valve in the pressure cap.
so you could run without an overflow bottle..
but you would always have an air space at the top of the pressure bottle..
It's just a better system to have a pressure cap with recovery valve in it,
and an overflow bottle.
Scott
www.turbovans.com
----- Original Message -----
From: "Michael Snow" <slowmachine82@GMAIL.COM>
To: <vanagon@GERRY.VANAGON.COM>
Sent: Friday, August 27, 2010 5:36 PM
Subject: Re: coolant system pressure
On Fri, Aug 27, 2010 at 12:31 PM, Marius Strom <marstrom@microsoft.com>
wrote:
> I believe the cooling system is rated for a max of 15 PSI.
>
> I'm curious, though, under what general conditions are you likely to
> achieve max pressure in this sealed system? I can think of a few
> variables:
>
> 1) as temperature increases, pressure should increase as well (however,
> the overflow pressure cap is what limits this to 15 PSI)
> 2) as water pump speed increases, there should be some increases in
> localized pressure (however, the overall system pressure should stay about
> the same - it's a sealed system, after all)
>
> What's the hive-mind say about this? If my thermostat housing drips a
> little bit at 15 PSI, but holds fine at 13 PSI, when am I likely to
> experience those last few bits of pressure? (Side note: I'm replacing my
> thermostat housing this weekend, but I assume the problem will just move
> to the next weakest link in the chain :)
>
A properly-sealed cooling system reaches approximately 15 PSI on every
drive that is sufficiently long to heat the engine and coolant to full
operating temperature. If it were not so, the overflow tank (behind
license plate) would be unnecessary. The worst-case scenario is when
the pressure-relief valve fails in the closed position and the cooling
system sees much more than 15 PSI. You'll find out quickly which hose
or clamp is the weakest link if this goes on for very long. I've
never see a clamp fail, but seen plenty of hose ruptures.
--
Michael Snow
1987 Syncro TiiCo
1982 Westfalia 1.9TD
http://slowmachine82.blogspot.com/
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