With a radiator overflow with its radiator inlet at the bottom is there a need to not fill the system and not leave room for expansion.

  Vic Correnti

If you have a coolant recovery tank then fill the radiator to the top. The only time you would leave expansion space is if you do not have a recovery tank.

Thanks

  Vic Correnti

The ‘need’ to fill (with a recovery tank) would be to thus have more coolant volume (assuming then, better cooling efficiency?).  I would also guess, that much like with oil in a larger crankcase capacity, life of the coolant would be extended.  The ‘need’ to NOT fill (no recovery tank) would merely involve the puddle on your garage floor, after the system contents expands when car is parked hot, and the expense of constant replenishment (assuming the system is refilled).
The benefits of enacting a closed system (higher boiling point, less corrosion, etc.) are usually best only with all new components.

6 VOLTS/POS. GRD. NW INDIANA

A larger volume of coolant would not affect cooling efficiency nor extend coolant life. The use of a recovery tank simply retains the coolant in the system instead of some of it winding up on the ground after a hot shut down. The same can be achieved by leaving expansion space in the upper radiator tank as original. A higher boiling point is achieved by using a higher pressure radiator cap and has nothing to do with the presence or absence of a recovery tank.

It IS true that a ‘closed system’ (recovery tank) has no direct relation to ‘boiling point’, unless compared to an ‘unpressurized’ system. Sorry (confusion on my part due to the fact that I run zero pressure).
But, while the % difference of volume here is so small as to be, in reality, insignificant, the principle re: the concept of coolant ‘volume’ vs. ‘efficiency’ would seem obvious, and to claim otherwise is likely nonsense (as anyone who has ever boiled water on a stove would know).
  Re: the lifespan/chemical stability of coolant formulas: the relation to volume could be irrelevant. Degradation from use (temp. cycling/mechanical circulation) & time (exp. date) probably wouldn’t be ‘volume related’ (?), unless concentration plateau considerations were involved (range extremes).



6 VOLTS/POS. GRD. NW INDIANA

Boiling a quart of water on a stove takes longer than boiling a pint of water. Is that what you're referring to? Eventually you wind up at the same point - boiling water. Other factors influence this, radiator cap pressure rating, coolant velocity through the radiator, heat exchange characteristics of the radiator core, air flow through the core, fin pitch, even the ratio of coolant to water in the system. Engine/head water jacket design also has an influence (think Ford flathead V8, one of the greatest contraptions for boiling water known to man).

I keep about 1/2” coolant in my 1 pt recovery bottle I made when cold. I’ve checked the bottle when the engine was at 200* and it was almost full; none has come out the bleeder. At 175* about 2” down. I have a US copper/brass radiator and a new heater core in the AC I installed so I changed to a 14 psi cap.

56 Vic, B'Ville 200 MPH Club Member, So Cal.

Coolant Velocity: Interesting subject by itself.
I’m reminded of the controversy re: whether removing the thermostat lowered max. coolant temp.  If I recall, it didn’t.

6 VOLTS/POS. GRD. NW INDIANA

You're correct, removing the thermostat doesn't reduce max operating temp, it will, however, increase warm up time which is not a particularly good thing. Coolant flow needs to be regulated so that the engine reaches optimum operating temperature quickly (thermostat closed), and then maintained within the optimum operating temperature range (thermostat opening and closing). Some of the flathead guys used to remove the thermostats and use fixed orifice restrictors instead. This may have worked OK for racing but I don't see it being beneficial for a street driven engine.