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Sorry for not snipping original msg more but needed
this much to maintain thought continuity.
Just as a data point, I will retell my
experience with coolant circulation loss.
Due to a malfunctioning pressure cap I lost
about 3-4 quarts of coolant on a flight back from an RV fly-in in Texas. I
was only about 10 minutes into the flight when this occurred. No
temperature clue to the coolant loss until it got below waterpump
level. Temp went from normal to redline in SECONDS. There was an
indication that something was wrong on the coolant pressure gauge which read
only 2-3 psi , which I chose to ignore. I was keen to get home.
(stupid - stupid - Stupid!)
I immediately reduced power and hit goto
nearest on GPS when the alarm went off and was about 8 miles from
nearest. Altitude was 3700 ft AGL. Temperature stabilized at
around 255 degrees but that may have been the upper limit of the GRT EIS.
Declared emergency and made a straight in approach & landing. Engine
continued to run normally throughout landing & taxi. Obvious hot
coolant smell when I shut down & got out to see the damage.
When I found the cap seal problem (& fixed)
I let engine cool and topped off the system with water. Coolant
pressure returned to normal and rest of flight home was normal. I'm
still flying this same engine which shows no ill effects from the
incident.
Here is the significant thing that I got out of
this. After the coolant loss below pump level, the temperature was
held to a "safe" temp by the remaining coolant in block being boiled
off. Conventional wisdom says that best place for waterpump is low
point in the system but in this scenario it may have resulted
in pumping the remaining coolant out of the system instead of leaving it in
the block to cool the engine from latent heat of steam. I credit this
factor with saving the engine.
Just something to think about when positioning
those EWPs!
Tracy
----- Original Message -----
Rusty,
I can see your
point. My ideas were motivated by my ambivalence around running both
pumps all the time (I'm uncomfortable with that for reasons that I can't
support really well) and the backup switch that turns on the standby pump in
the event of main pump failure (that's an unknown quantity to me as far as
reliability goes). I was looking to examine as many failure modes as
possible. Of course, as just occurred to me, the backup pump switch
would be exactly as reliable as the overtemp alarm, since they'd both be
driven by identical (if not the same) detection device.
You're right in saying that we both have to make our own estimates of the
unknown consequences of various failures, and you're the man in the driver's
seat here. Keep up the good work. Your research is going to
relieve me of that chore. Don't think I don't appreciate that.
Russell Duffy wrote:
If it was me, I'd do a little testing - start at cruise at
altitude - and shut off the pump and see what happens and how fast.
I'll just have to wait and see how
it works for you, because there's no way I'm doing it. I think you're
closer to underestimating the damage, than I am to overestimating it, and if
I have to be wrong, I'd much rather be on the safe side.
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