[TR] tr3 open/closed radiator system

[Randall]

> so what are the advantages and disadvantages?

The main advantage, IMO is that it keeps the radiator completely full
instead of having air space at the top.  That increases cooling slightly,
but more importantly helps keep air from getting mixed with the coolant.
Without it, I always see a little bit of foam on top, which says to me that
air is getting trapped and carried through the system.  And obviously air is
not as good a coolant as water.

> will the overflow
> have to be higher than the fill neck of the standard 
> radiator.

The optimum configuration is supposed to be the overflow roughly parallel
with the top of the radiator.  However, most later Triumphs have the bottle
down low, so it must work reasonably well that way.

> is their anything special about the installation? just add tubes and
> match the psi of the 2 fill caps?

Normally, if the bottle is pressurized (as it appears your MG bottle is),
the cap on the radiator is a dummy cap, permanently open to the tube to the
bottle.  But I don't see any reason it wouldn't work with a pressure cap in
both places.  Don't forget that the tube from radiator to bottle now has to
handle pressure (use reinforced tubing rather than standard overflow
tubing).

However for this to work, the radiator cap needs to seal air-tight to the
uppermost part of the neck, which the stock TR3 cap does not.  Perhaps some
of the replacements do though.  Look for a rubber ring (instead of brass)
inside the outer lip of the cap.  I had my radiator modified with a shorter
neck, so I can use standard caps instead of the TR3-specific one.  Cost was
less than $20 (but they were doing other work on the radiator at the same
time).

> and while we are talking radiators, whats
> the thoughts on advantages of a higher pressure radiator? it 
> raises the
> boiling point but not the operating temperature.

Increase in boiling point is the main advantage, IMO.  Gives you a larger
margin under conditions where the coolant temperature goes up (like a sudden
stop after driving at speed).  However, at least in theory, the higher
pressure also improves heat transfer to/from the coolant, which may improve
cooling slightly.  I've never really been able to tell the difference
myself.

Randall