Gary,
The bellows will not always collaps in the sense that they get damaged.
Because of the higher external pressure the bellows will contract until
the vapour pressure (sorry I do not know and cannot find the correct
English term) of the medium in the bellows (probably aether, ethanol,
methanol or similar or a mixture) is the same as in the cooling system,
thus effectively (partly) closing the thermostat. This means that the
coolant temperature has to rise to open the thermostat again, hence the
higher readings. In effect by raising the pressure in the cooling system
you also raise the opening temperature of the thermostat. By returning
to the lower cooling system pressure the function of the bellows
thermostat will return to normal again.
Raising the coolant temperature at the higher pressure is no big deal.
In effect it will create a more efficient engine and a better heat
transfer as the Delta T between radiator and air is increased.
I have always raised the operating temperatures ( usually between
82-960C) on my cars, adding if necessary an expansion vessel, a bigger
radiator and a thermostatically controlled electric fan and often also
raised the pressure as to prevent boiling.
You can still use a bellows thermostat, but you cannot rely on its given
opening temperature. Determine that when it is installed when you watch
your temperature gauge.
Kees Oudesluijs
NL
Op 31-3-2013 21:45, warthodson@aol.com schreef:
> Kees,
> You are correct, however I am assuming an original Healey type cooling
> system without an expansion vessel & an original style radiator cap.
> I agree that if the radiator is filled with water such that there is
> very little air in the system, then initially the non-compressible
> water will expand & the pressure will rise up to the pressure rating
> of the cap. At that point the "excess" water will be expelled & the
> available space will be replaced with compressible air. From then on,
> I do not believe the heated water & compressible air will ever reach
> the pressure rating of the cap, unless of course the water
> temperature rises above 212F to the pressure/temp equivalent of the
> specific cap.
> David nock's explanation is based on the assumption that the
> thermostat is a bellows type & the bellows is operating correctly at
> or below 7 PSI & the bellows is collapsing at a pressure somewhere
> between 7 PSI & 10 PSI. This does appear to be a
> logical assumption/explanation. However, I believe the original post
> indicated that the temperature returned to normal after the 10 PSI cap
> was replaced with the 7 PSI cap. I would think that if the brass
> bellows had collapsed it would not function correctly at the lower
> pressure.
> Replacing the thermostat with the type David describes is the logical
> next step. The only thing I do not like about those thermostats is
> that they are 160 F. Of course, most of our driving is such that
> the thermostat will be wide open & the operating temp will reach
> equilibrium at some temperature independent of the thermostat control
> temp.
> Gary Hodson
> From: Oudesluys <coudesluijs@chello.nl>
> Gary,
>
> This is not necessarily correct. If there is little or no air in the
> system the pressure will certainly rise to the limit of the rad cap as
> the water will expand and as it is non-compressable the pressure will
> rise considerably. This is often the case with an airtight rad cap and
> if a expansion vessel is fitted.
>
> If there is a lot of air in the radiator, the pressure will not
> increase a lot as the air will be slightly compressed by the expanding
> water and the increase in temperature.
>
> Kees Oudesluijs
>
> Geen virus gevonden in dit bericht.
> Gecontroleerd door AVG - www.avg.com <http://www.avg.com>
> Versie: 2013.0.3267 / Virusdatabase: 3161/6216 - datum van uitgifte:
> 03/31/13
>
--
Kees Oudesluijs
Dorpsstraat 183
2995XG Heerjansdam
T: 078-677 1233
E: coudesluijs@chello.nl
Technische commissie Jensen Healey en GT
Het Jensen Genootschap Holland
www.jensenholland.nl
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