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Hard to say, Peter
You may have a problem or may
not. After some flights my coolant pressure will remain at 7-10 psi
for days or even weeks, other times it goes down as soon after I shut down the
engine. I also have my coolant pressure go as high as 20 psi on start up
(long before the coolant would be hot enough, you would think). My first
thought was that I had a leak in one of the coolant "O" rings that was
permitting the combustion gases to pressurize the coolant system.
I have now been flying with
those conditions for over 80 hours. However, on this engine (91 turbo II) there has been no lost
of coolant and the pressure drops to an average of 5-7 psi in flight and
sometimes when the coolant and oil temps drop below 160F - no coolant pressure
shows (I do not have a thermosat). By increase the power/rpm the temps
will rise and the pressure gauge will start showing pressure again.
My theory (so you know what that is worth) is that
if you have been successfull in evacuating all the air from the coolant system
then you have essentially an incompressible liquid left (actually, there is
still a small amount of air remaining, in solution with the coolant, if nowhere
else). So I believe even the the coolant pump running could create
pressure readings depending on where you have your sensor. I notice
that if the pressure is up around 20 psi immediatly after starting the engine
and (after warming the engine up) I reve it to 5200 rpm that the coolant
pressure drops to 5-7 psi while at the higher rpms. It would seem to me
that if the pressure I am seeing on start up were truly combustion gases leaking
past the "O" ring then at 5200 rpm the pressure should increase - not decrease.
Plus the fact that the coolant pressure when flying is never higher than 15 psi
leads me to believe that this may not be a problem as it first
seems.
Now I could be all wet with this theory, but
I would look for other signs of a true problem. Are you seeing any green
coolant leaks around your intake or exhaust system. Any signs of bubbles
or exhaust smell when you open your radiator cap?? Etc.
The reason I think the pressure decreases (In my
installation)when I reve the engine is that I have my pressure sensor in my
header tank. My header tank ties in to my coolant line with a "T" just
before the pump intake. So I believe that the flow of high speed coolant
past the opening of the "T" tends to create a low pressure area in the header
tank where my sensor is located.
On a previous engine (an 86 NA) I did develop a
coolant "O" ring leak when I badly ( and several times) overheated the
engine. It caused me to slowly lose coolant at a gradually increasing
amount on each flight and eventually forced me to tear down the
engine. Also, green coolant began leaking from my exhaust pipe which
cinched the diagnosis of a coolant "O" ring problem. I found the leak next to
the exhaust port in the inner coolant "O" ring. So after that I went with
the Tefolon Coated Silicon "O" rings from Hayes and believe they have held
up.
So don't know if my experience helps any, but there
you have it for what it may be worth.
Ed Anderson
----- Original Message -----
Sent: Monday, December 16, 2002 8:53
PM
Subject: [FlyRotary] water pressure
Today I'm seeing some different characteristics
in the water pressure readings. Used to be that after cooling down I could see
4 or 5 lbs pressure for many days and I don't think increasing pressure after
start up was tied to rpm. Now pressure drops instantly on shutdown and is
closely tied to rpm to max of 15lbs as the engine is reved up. This looks bad
to me although temps in flight are fine. What do you think?
Peter
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