----- Original Message -----
From: "Richard" <unicorn@gdsys.net>
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Sent: Thursday, March 04, 2004 12:41 PM
Subject: [FlyRotary] Re: Ideal Cooling System Plumbing (was Re: [FlyRotary]
Re: overflow connections


> As long as the coolant temperature is below the boiling point, pressure
> would be the only indication of a leak. Once the boiling pressure is
> reached, the temperature indication again does not increase until the
> temperature sensor is getting out of the liquid coolant.
> Therefore, water pressure gauge!

Actually, it will be both, if you have 2 temp sensors - 1 somewhere away
from combustion chamber area and 1 right there.   Ah, I think I'm mixing
"plugs up" and "plugs normal" talk here - the "early warning" I've been
talking to must only be applicable to "plugs up", with the hottest part of
the block up.
1.   In that "plugs up" case (new qualifier) as the coolant level goes down
the first little bit and some of the water passage right at the combustion
chamber becomes dry, localized nucleate (or worse) boiling will start and
the 1000 to 1 expansion ratio WILL cause "slight, jiggley" pressure
fluctuations, mayabe 2psi above normal (I'm paraphrasing what I've heard Ed
say - hope IRC).  HOWEVER, the steam will condense back to water as it flows
downstream from the hot spot, so a later temp sensor will only see/display
"normal" (or near normal) temp. Same for the "early warning" temp sensor
nearest combustion chamber - it is still immersed in "normal temp" coolant,
so no warning yet.
    -  Yes, pressure jiggles are first indication, for plugs up.
2.  Continuing for plugs up, as the coolant level goes down below and
uncovers the "early warning" temp sensor, it changes from "coolant temp" to
"CHT" and goes up rapidly to local metal temperature instead of water
temperature. (not sure how this would look, as sensor is on opposite side of
water jacket from side actually touching hot combustion gases).  Anyway,
there is where the "early warning" coolant temp sensor would be of some
value - in confirming that you ought to be seeing "pressure jiggles" and get
on the ground.

This must all be "not applicable" to "plugs normal" - as the plugs and
combustion chambers are at 3 or 9 o'clock (side) of engine - and any "early
warning" temp sensor there would not be uncovered until half the block was
empty - way too late to know.
    -  So, "pressure wins over temp", especially for "plugs normal". (I've
been "raised" on reading Ed's plugs up stories!!  Sorry for the confusion.)

3.  However, with ref to my last input, "coolant level", as sensed inside a
"pressurized" coolant expansion tank - IF mounted with coolant level up near
top of engine , will be the ABSOLUTE first AND BEST indicator of a leak:
Coolant leaks out - anywhere, that coolant is replaced by coolant in
"expansion/reservoir/pump header" tank until tank empties/turns on "Low"
light.  Up to this point, the engine is FULL of liquid - no air, no nucleate
boilng, no temp jiggles.  Then subsequent leakage will be out of engine, as
"expansion/reservoir" tank is now empty - THEN, the PRESSURE jiggles will
start.

David