I offer the following in response to the recent coolant-recovery discussion:
A 1:1 mix of water and ethylene glycol anitfreeze has an expansion coefficient
of about 700ppm/degree C, or in more convenient terms, 0.04%/degree F. Thus,
if an MGB radiator is topped up with coolant at a temperature of 60F, the
coolant will expand 4% at an operating temperature of 160F (or about 4.7% with
a 180F thermostat). Given the 1.5 gal capacity of the cooling system, incl
heater, this represents an increase in volume of just under 1 cup (or just
over 1 cup at 180F).
With the possible exception of expansion of the radiator hoses accomodating
a smidgon of this volume, this much coolant *must* be discharged (out the over-
flow tube) by the time the engine first reaches operating temperature.
That is why you can't (and shouldn't try to) keep the radiator topped up.
Just to verify all these high-powered calculations, I topped up my B's
radiator last night: I'm here to tell you that it took 8.000 ounces!
(Well, about a cup anyway.) The pavement awaits the deluge....
Any loss greater than this means either you have a leak or the engine is
operating hotter than you think because the thermostat sticking closed, the
radiator is clogged, etc. (Unfortunately, in my experience, thermostats are
more likely to stick open and it's usually the radiator causing overheating.)
I have found that a common leak source is the rubber gasket under the radiator
cap. The gasket is inconspicuous and easily overlooked. Even worse, it
discretely discharges its waste down the overflow tube so the leak easily
goes undetected. (And, of course, a leak prevents pressurizing the
system so you don't get the benefit of an increased boiling point if things
should really get hot.)
BTW, I believe the primary benefit of the closed coolant systems, which I did
not see mentioned in the recent exchange, is that they exclude air from the
radiator and, after numerous heating cycles, will even allow much of the
disolved air to be purged from the coolant. This inhibits corrosion, which is
an oxygen-demanding process. Ever notice that the worst rusting on marine
equipment occurs at and just above the water line where moist metal is exposed
to air, while the completely submerged metal lasts longer. Since MG's don't
have this benefit you just have to count on the protection of a good antifreeze
(which means you remember to replace it every two years to renew the corrosion
inhibiting ability, don't you).
RsW
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