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RE: REFLECTOR: Oil temperature
To all you Franklin Reflector listeners.
I had a long conversation with someone at Oshkosh who have the STC on
the Franklin engine in Cessna and Stinson airplanes. He told me he uses a
firewall mounted Contentinal type vernatherm valve instead of the spring
pressure valve. He said high oil temperatures on both were solved with
this system. Price complete was under $200.00. All my information is in
the motorhome on the way back from Oshkosh. I'll post more on this when
Scott gets back.
Duane
-----Original Message-----
From: Gilles & Denise Gratton [SMTP:gratton@magma.ca]
Sent: Friday, July 23, 1999 10:31 PM
To: reflector@awpi.com; mathieu.gratton@sympatico.ca
Subject: REFLECTOR: Oil temperature
Hi folks!
I recently completed my first 25 hrs of test flight and C-GDOU is
now spreading its wings out of the 25 miles restriction. That test period
went well and all minor snags seem to have been taken care off. Next week
is the ultimate test on the trip to Oshkosh.
My homebuilt prop is performing well. It is giving me 2600 rpm on
take off and tends to have good cruising characteristics. The next one
that I will build will have probably a finer pitch to sacrifice a bit of
speed to improve take off on my short homebase runway. I simply use up too
much of that runway at gross weight to be comfortable (the top of that
grain bin at the end looked awfull close).
Naturally upon pushing my Franklin engine to higher speeds I ran
into oil temperature problems. 230 degrees at 2300, 240 at 2400, 260 at
2600, etc.
This in spite of using the factory`s stiffer bypass spring, ducting cold
air along the oil line duct, maximizing air flow to the oil cooler with an
improved naca duct system, etc. My CHT readings on all cylinders were all
very low, in the 175 to 225 degree range. My scoops and plenum must be
working very well. Has anyone else got these low temperatures? I have
calibrated my probes before installing them and they were normal. The first
few times that I ran the engine on the ground I got higher readings if I
let it run too long. So I assume that my readings are true.
I then looked at the oil pan and thought that all this big surface area
with fins at the bottom could be cooled better to improve the oil temp. So
I built a seperate plenum under the oil pan (3/4 inches all around the pan)
and built small scoops within my bigger air scoops to run dual 2 in. scat
tubing to this plenum. Well that helped, brought the oil temp. down by 10
degrees at all rpm regimes. CHT temps only went up by about 20 degrees. I
was still not satisfied with the oil temp.
I then put temp probes on the inlet and outlet of the oil cooler to
analyse what was going on there. Results... engine 240 degrees, in the
cooler at 240 also, out the cooler at 190 degrees. Great, my cooler is
doing a fastastic job cooling that oil, 50 degrees! No, no, no....that
tremendous cooling simply means that there is very little oil flowing thru
the cooler, no wonder it has time to cool by 50 degrees. So I assume that
oil is by passing the cooler in spite of the stiffer spring. Well guess
what? I ran to the hardware store to get a stiffer spring yet. I put it in
and off I go. Twenty minutes into the flight at 2600 rpm and my temp is
still 210 degrees. I can live with that. It now comes in the cooler at 210
and comes out at 190. Only 20 degrees difference. Oil must be flowing to
the cooler now instead of bypassing it. I tested my new spring at 35 psi
instead of 24 psi for the "stiff" one supplied by the factory and 14 psi
for the original one on the Franklin. I figure that this 35 psi is still
safe and will allow bypass in case of blocking in the oil flow since the
engine oil pressure is higher than this.
All of this I did to avoid putting an extra oil cooler or to
increase the size of the oil lines as I believed that any restrictions in
the oil fittings would limit the oil flow anyway.
See you in Oshkosh. Gilles C-GDOU LW FG Elite