From: "Marvin Kaye" <marv@lancaironline.net>
Subject: Re: Oil Cooling (It's a Delta P Problem!)
To: lml
Date: Sun, 05 Oct 2003 17:50:19 -0400
Message-ID: <web-2625191@logan.com>
In-Reply-To: <BIEPIMPOCOCOMPKFKIKGCEIODEAA.ngarvin@comcast.net>
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Posted for "Neal Garvin" <ngarvin@comcast.net>:

We had the same problem with our Glasair oil temps hitting 245 on climb out.
The cooler was getting air off the back of Cyl #3 with a 3" scat tube. The
cooler was mounted on the side of the cowling with the cooler exit air
dumping into a hood and then through scat tube to a 4" x 4" louvers on the
bottom of the cowling. This didn't work at all.

Just by removing this exit hood and scat from the exit side of the oil
cooler, and letting it dump into the lower cowling reduced oil temps
significantly. We then added reverse scoops to the bottom cowling louvers to
get more air out of the lower cowling area. This reduced the temps even more
(both oil and cyl temps).

During all of our testing and trial & error modifications, we found the most
significant improvement came from adding small reverse scoops over the front
of the louvers on the bottom of the cowling. These added some venturi effect
to suck air out of the lower cowling area. Since the oil cooler air was
dumping directly into the lower cowling area, the oil temps instantly went
down 25 degrees.  This proved that we had a problem with airflow THROUGH the
cooler which was caused by excessive backpressure on the cooler, not
inadequate supply air.

I'm not sure what your cooler mounting looks like, but the heated oil cooler
air should exit directly to a low pressure area and if there is any type of
hood arrangement on the backside of the cooler, it should be very large. The
air going through the cooler is heated and it expands. The exit area of the
cooler shroud/hood would need to be at least 50% larger than the intake
area.  I'll bet your "escape box" is much to small and is causing all of
your oil temp problems.

One way to test this:  make up a fiberglass or aluminum small reverse scoop
that sticks out about 1" and covers over the front 1/3 of your louver gills
on the outside of the cowling. You can use lots of package tape to hold it
in place.  This will reduce the pressure in your "escape box" and should get
more air flow through the cooler. Go for a test flight and the oil temps
will be lower.

How you permanently fix the problem will probably require removing or
redesigning your "escape box".  We chose to not use the reverse scoops
because of the increased drag and ended up using a larger oil cooler mounted
directly to the side of the cowling for direct air exit through a louver.

In all my travels and meetings with many other experimental builders, I have
yet to see a problem with pulling air off the back of the baffling to feed
an oil cooler.

We now have a 4" scat coming off the baffling behind #3 cyl and we have no
problems with cyl head temps.  Don't waste your time with another naca scoop
for oil cooler air. There is plenty of air going in the front of the
cowling.

It is also incorrect to assume that the air that pass over the tops of the
cylinders is being heated before it goes to the oil cooler. It may see a
degree or two increase, but that's probably it.  Air going into the cowling
anywhere near the cylinders is going down between the cylinders and fins. It
can't back up and then go to the oil cooler. The only mixing of any slightly
heated air is minimal.

Put on a reverse scoop and see what happens.  Good luck.

FYI, Burt Rutan did an article about oil cooling problems he had many years
ago with the original EZs and adding a reverse scoop under the oil cooler
exit solved the problem.

-Neal Garvin
Glasair SIIS-RG
IO360 20 HP