[TR] 4lb TR3 Rad Cap

Randall tr3driver at ca.rr.com
Mon Feb 27 11:41:18 MST 2012

> 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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