I have a feeling that we are talking about two different "coolant level
sensors".  The one I'm talking about is in the "pressurized
coolant/expansion/header tank" like a late 90's Ford Taurus.  The point that
must be noted to discuss this "logically" is that the coolant level in this
tank ("FULL - HOT") is ABOVE the top of the high spot for coolant in the
engine.  And, there is air space above the FULL- HOT level.  There is not
other expansion tank.   Coolant doesn't go "somewhere else".  That is as
high as the level gets (unless there is blowby which is discussed last
below.)  But, to discuss LEAKS, not BLOWBY/STEAM:

This being the case, if the coolant level in this tank goes down and  the
"low" sensor activates, there is still coolant in the engine block (unless
the coolant tank is very deep, where bottom is WAY below the top of engine -
not the case on the Ford).  If this is so, then how could the "coolant low"
light NOT be a good indicator that you have a leak?
    -  None of the coolant is being "expanded" into an unpressurized
"expansion tank".  That unpressurized tank is REPLACED by this "pressurized
coolant/expansion/header tank".  Coolant does not "expand" "OUT" of this
tank.  It is THE expansion tank.
    - I think we are mixing the two systems in this discussion.   This
"pressurized coolant/exp/hdr tank" is part of the CLOSED system - it is not
"external" to the cooling system.  It is PART OF THE SYSTEM - and if its
level goes down, then the entire closed system is losing coolant - the
SYSTEM has a leak.
    -   When the sensor in this tank turns on the "low" or "check coolant"
light, then you have a leak - and you know it immediately upon losing  about
1/2 or 1 qt (whatever is in this tank between "Full - Hot" and the "low
sensor".

Yes we should know the pressure indications of problems - but I don't think
we have anyone flying with a tank with a fluid level indication system.
Thus, there will be no "real stories" to validate this proposed Ideal
Cooling System. (ref someone else's post asking for "proof").

And, yes, if there is blowby as mentioned earlier (compression/combustion
gasses leaking by bad seals into the cooling passages and forcing HIGH
pressure into the coolant galleys) then, because this high pressure is
greater than the cap's release pressure, this blowby WILL force liquid past
the cap and out wherever you have it plumbed to go.
    -  I would simply route the rubber line from that "cap pressure release
overflow fitting" to go up and spray up beside the windscreen where I could
see it - to warn me that I was either suffering compression blowby - either
from bad seals or from overheating and steaming.  In either case, I'd have
instant warning that I need to terminate the flight ASAP.
    -  It would be an desireable increase in parts count and would MASK the
problem to vent the "pressure cap blowby" into some other "expansion tank"
that you couldn't see or might not immediately notice.

In summary, in the absence of "high pressure above cap release pressure" in
this CLOSED system, a fluid level indicator system should give you an early,
positive, and adequate warning that you have a leak, whether you notice the
pressure "clues" or not.

David

----- Original Message -----
From: "Tracy Crook" <lors01@msn.com>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Sunday, March 07, 2004 10:33 AM
Subject: [FlyRotary] Re: Ideal Cooling System Plumbing
(wasRe:[FlyRotary]Re:overflow


>   FIRST the pressure drops precipitously, and THEN the coolant level
> starts to go down ... FINALLY the temps start to rise (provided the
> temp sender is submerged in what water remains).


Just a brief comment on this part.  Coolant level sensors are of almost no
use in this application.  It is commonly assumed that the temp gauge reads
low as soon as the sensor is no longer submerged.  Not true.  It only drops
after the coolant is all boiled away because steam will heat the sensor.  If
you haven't caught the problem long before this, it's too late anyway.

Tracy