Hi Bob
The Rad cap is also described as a PVRV, or pressure vacuum release valve,
you have the big rubber seal that makes to the bottom of the filler neck,
this deals with the pressure relief and in the middle of this is the vacuum
release valve with a very soft spring on it, the pressure of the spring is
just enough to make a seal, as the pressure rises it presses on this disc
and pushes it closed. As the coolant expands it lifts the whole lot to
escape. As the engine cools the pressure diminishes and then becomes a
vacuum, this is sufficient to allow the air pressure acting on the coolant
in the expansion bottle to push the coolant back up the hose and push open
the vacuum release cap an return to the rad, any leak in the hose will allow
air to enter the system in preference to the water.
All the Triumphs I have except the Dolomite (which uses the pressurised
header tank principle) have this coolant recovery system, and it works!
How to tell, make a mark on the expansion bottle after a refill and then go
for a drive, when you return with a nice hot engine, open the bonnet and
switch off the engine, the coolant should be some level higher than the
mark, watch as the engine cools and you will see the coolant start to be
drawn back in. Chances are it will only draw back 75 to 90 percent of the
amount that was expelled during warming, this is due to differences in level
and efficiency of the system.
Hope this helps!
Graham.
----- Original Message -----
From: "Kinderlehrer"
Subject: Re: Two TR3A radiator questions
> Anyone know what magic makes it work?
>
> Bob
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