[TR] 4lb TR3 Rad Cap

spook01@comcast.net spook01 at comcast.net
Mon Feb 27 12:03:09 MST 2012

Another consideration is the ability/design of components such as the heater core.
On the Sunbeam Tiger, a lot of heater cores are "pooched" out because the design pressure limit has been exceeded by guys seeking boilover protection by going to 15 psi caps.
The 4 psi cap works as designed, allowing the expansion tank built on to function pre design.
The aneroid t stat is no doubt one of those components. 
Just saying....

Sent from my Verizon Wireless Phone

----- Reply message -----
From: "Randall" <tr3driver at ca.rr.com>
To: <triumphs at autox.team.net>
Subject: [TR] 4lb TR3 Rad Cap
Date: Mon, Feb 27, 2012 12:41

> I have often wondered why the TR3 cooling system only has a 4lb
> pressure cap.

I believe that is because the original thermostat was an "aneroid" type,
where the pressure inside the bellows opposes the pressure outside the
bellows to determine the thermostat position.  As the pressure outside the
thermostat rises, it takes a higher temperature to open the thermostat.  At
any rate, my TR3 seems to do just fine with a 10 lb cap and a modern "wax
pellet" thermostat.

> I have never heard any definitive data on just where the line should be

The "definitive data" IMO is how much it will hold without losing through
the overflow, under all operating conditions.  As you have seen, and others
reported, halfway is too much (even though I believe it is documented that
way on page 13 of Practical Hints 6th ed). 

Of course it is possible you have some other issue, like perhaps a tiny
headgasket leak.  BTDT  But I think you'll find that, if you leave it alone,
the water level will go down a bit and no more.

-- Randall 

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