[TR] 4lb TR3 Rad Cap

Jonas Payne JPayne at ThorCon.net
Mon Feb 27 15:13:38 MST 2012

As the owner of 2 TR3 powered +4 Morgans as well as a TR3, I can tell you that
you absolutely don't want to put in a cap higher than 6 pounds, you blow out
the squirrel cage smiths heater.

Also, I don't  believe that the soldering in a Morgan rad made of too stern a
stuff, as you can blow out the rad too.  (The TR one seems to be a bit higher

Jonas Payne
Cell:   (702) 358-5084

-----Original Message-----
From: triumphs-bounces at autox.team.net [mailto:triumphs-bounces at autox.team.net]
On Behalf Of Randall
Sent: Monday, February 27, 2012 10:41 AM
To: triumphs at autox.team.net
Subject: Re: [TR] 4lb TR3 Rad Cap

> 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"

> 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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