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Subject:Re: Cool Running Rotax 447
From:Vince Calhoun
Date:Mon Nov 20 23:03:20 2000
I did the same thing, install a free-air-scoop to get better cooling on my 447.
I also removed the fan, shaft, and all that extra mess.
When I was fan cooled my 447 CHT would climb to 440F on climb out
With the scoop I can sometimes get to 410F, but usually not, typical CHT on
climb out to 1,000 AGL is 400F.
I do my CHT spark plug ring sensors a little differerent than most folks I think.
Because I know the CHT temp often lags actual temp by at least 20 degrees
with a normal underplug seating arrangement, I have fashioned a thin SS washer
to go over the ring sensor- thermocouples. They look like a normal fender t ype
washer, lots of metal area. I coat the washers with silicon grease, along with
smearing a coat of silicon grease on the thermocouples. The silicon grease
insures good thermal coupling (heat transfer.) This helps more accurate readings.
Another benefit is now it is easy to remove a torqued plug and put in a replacement
without damaging the spark plug CHT senders! Those senders were getting
mutilated by 240 ft lbs of torque and twist every time I changed plugs!
Normal cruise temps for me have been 350 to 370 Degrees F. EGTs of
900F climb out, 1050 to 1100F cruise. My 447 runs so good it scares me.
Particularly because I have 278 hours on it now, and the magic 300 hour tick
is fast approaching!
The only problem Ive ever had with the 447 is my ignition coil failed at
62 hours. I learned immediately about emergency dead stick landings!
As a related matter, it has been my experience that the Rotax 5,000 Ohm
spark plug caps are inferior to the NGK type 5,000 Ohm caps. I use only
NGK BR8EV, gapped at .020 thousandths, with my NGK plug caps.
Just to round out the story and fix conditions, I use only Pennsoil
Air-Cooled 2 cycle engine oil mixed 50:1
End of data!

Vince Calhoun

"Jbmmax1" wrote in message
> I recently installed a CPS Air Scoop on my Rotax 447 because it was running too
> warm with CHTs always around 400 F even in cruise. I could not sustain climbs
> or the temperatures would start up over 425 F. I have been pleased with the air
> scoop, and my engine is now running between 275 & 300 F during cruise in the
> cool fall air (around 50 F). Yesterday I was told by some "old timers" that my
> engine is running too cold. Do some of you experts have an opinion on this?

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