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overflow tank question

To: "David Lee" <davelee1@home.com>
Subject: overflow tank question
From: Dave Massey <105671.471@compuserve.com>
Date: Tue, 15 Feb 2000 11:37:14 -0500
Cc: TR List <triumphs@autox.team.net> charset=ISO-8859-1
>Is the radiator supposed to always be full or is it proper for there to be
a
>little emptiness to make up for the expansion of hot water?  Is the
overflow
>supposed to somehow get sucked back into the radiator?
>
>Thanks
>David Lee

Dave

Modern cooling systems (including the TR6) with an overflow recovery 
system use a radiator cap with two sealing gaskets.  The first gasket 
seals the throat and provides a preasure seal allowing the system to 
build up pressure.  The "plug" is spring loaded and when the pressure 
overcomes the spring the plug will allow coolant to flow into the 
recovery bottle.  This plug also has a check valve that will break 
vacuum as the system cools down.  

The Second seal is just under the cap and seals off the overflow tube 
connection from atmosphere.  This seal ensures that when the 
pressure relief action takes place the coolant is routed to the recovery 
reservoir and when the vacuum breaking action takes place coolant is 
drawn from the reservoir (This is why the tube must extent down to 
near the bottom of the reservoir).

If the second seal is leaking (or if the tubing is leaking) there might 
be evidenceof a coolant leak but the first symptom is air is sucked 
into the radiator instead of coolant.  A properly functioning cap and 
recovery system will eventually purge all air out of the cooling system.

Sorry for the long winded answer but the system is more invloved 
than one might expect.

Dave Massey

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