All modern cooling systems are closed. It does not matter where the pressure
cap is located, (radiator or catch tank) the effect is the same, as to
pressure in the system.
Herb Miller
-----Original Message-----
From: healeys-bounces@autox.team.net [mailto:healeys-bounces@autox.team.net]
On Behalf Of Eric (Rick) Wilkins
Sent: Monday, July 26, 2010 10:42 PM
Cc: healeys
Subject: Re: [Healeys] Overheating Healey (closed system)
As coolant gets hot, it expands. Since the cooling system is sealed,
this expansion causes an increase in pressure in the cooling system,
which is normal and part of the design. When coolant is under
pressure, the temperature where the liquid begins to boil is
considerably higher. This pressure, coupled with the higher boiling
point of ethylene glycol, allows the coolant to safely reach
temperatures in excess of 250 degrees.
The radiator pressure cap is a simple device that will maintain
pressure in the cooling system up to a certain point. If the pressure
builds up higher than the set pressure point, there is a spring loaded
valve, calibrated to the correct Pounds per Square Inch (psi), to
release the pressure.
When the cooling system pressure reaches the point where the cap needs
to release this excess pressure, a small amount of coolant is bled
off. It could happen during stop and go traffic on an extremely hot
day, or if the cooling system is malfunctioning. If it does release
pressure under these conditions, there is a system in place to capture
the released coolant and store it in a plastic tank that is usually
not pressurized. Since there is now less coolant in the system, as
the engine cools down a partial vacuum is formed. The radiator cap on
these closed systems has a secondary valve to allow the vacuum in the
cooling system to draw the coolant back into the radiator from the
reserve tank (like pulling the plunger back on a hypodermic needle)
There are usually markings on the side of the plastic tank marked Full-
Cold, and Full Hot. When the engine is at normal operating
temperature, the coolant in the translucent reserve tank should be up
to the Full-Hot line. After the engine has been sitting for several
hours and is cold to the touch, the coolant should be at the Full-Cold
line.
On Jul 26, 2010, at 7:57 PM, Bob Spidell wrote:
> re: "A closed system with a return tank raises the boiling temp"
>
> How?
>
>
> bs
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