I'm sure that "not" was intended.  However it took me some headscratching
to see how that would affect pressure buildup, as vapor pressure of coolant
would be constant at a given temperature -- until I realized that there are
two different mechanisms involved.

Initial pressure results from straight expansion of liquid coolant against
the confines of the cooling system.  Sixteen liters of 50% glycol coolant
expands about half a liter going from 30C to 100C.  Any air in the system
would have a lower "spring rate" than the hoses, and would thus reduce the
overall pressure -- until boiling, micro or otherwise, began; at which
point the ultimate pressure would be controlled by the temperature in the
hottest submerged section of the system, as vapor would be generated
(quickly or slowly) until the equilibrium pressure was reached and the
boiling stopped.

All heat-generating portions of the system must be submerged to avoid
severe local heating, as steam has greatly inferior heat transfer ability
compared to liquid.  Same problem with micro boiling, it interposes a
low-conductivity layer between the heat source and coolant.

Yrs,
d

On Sun, May 21, 2017 at 11:45 AM, George Gaudette <gcgaudette@gmail.com>
wrote:

> Can someone say a few more words about this?:
>
> "If the engine is completely filled with coolant the system will not build
> pressure and micro boiling and vaporizing will do damage to the cylinder
> walls and head studs"
>
> I'm thinking the word "not" might have been accidentally left out ("If the
> engine is **not** filled...").  If so, not further explanation requested.
>
> -George
>