My latest thought on the surprising amount of
overflow is based on the time when it occurs.
The overflow (from the 1 qt. bottle) would occur
during prolonged periods of full throttle operation and was a relatively fixed
amount (2 - 3 oz). I now hypothesize that local boiling (nucleate
boiling) in the combustion chamber (CC) area of the cooling jacket is
increasing the volume in the system. Local boiling creates steam bubbles
which are immediately swept away from the wall and are almost immediately
condensed to liquid again because the bulk coolant temperature is
well below the boiling point.
The temperature of the CC wall is still above
boiling point so another bubble of steam starts forming after the first is
swept away. The "life span" of these steam bubbles is very short
but at any given moment, there are thousands of them being
"born".
This activity stops immediately after power is
reduced to the point where heat is carried away fast enough to eliminate
nucleate boiling. Volume then drops in the cooling system to normal
conditions.
I suspect this rarely happens in a car because
the engine is never at WOT for more than a few seconds. Even race cars
back off in the corners which give the CC walls a chance to cool off a
bit.
Just another theory,
Another factor that affects the coolant volume is the
expansion of the metal in the engine. The coolant is essentially
contained in an annular region around the rotors. The inside of that
annulus gets pretty hot. Could be that the coolant capacity in the
engine is decreased.
I have no idea how big a factor this is, but it seems
that that overall coolant "expansion" is more in a rotary. I'd estimate
that the amount of coolant that gets pushed into the catch bottle on the V-8
in my van is a pint or less.
Al
.Tracy
and others, what is the theory behind so much liquid in the
external
expansion tank? Thermal expansion of the initial coolant volume
doesn't
account for such a large overflow. So is vapor building up
inside? If it is
there is no longer a liquid filled system. I don't get
it.
Peter
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