Oil Cooler Throttle Valve
Here's a project I actually completed last fall, but am just
getting around to posting. Since 2016 when I started flying
the RV-14A, I've had excellent oil temperatures and CHTs at all
times. It's the best cooled engine I've ever operated,
actually. But that becomes a problem when you live in the
North Country. When we get temps even down in the 30s, there
are many times when I can't get the oil temp even out of the
170's. I can even see CHT's in the low 200's on the colder
days. An engine really needs to get up in the mid-180's for
Oil Temp, if you're wanting to help get rid of rust-causing
moisture in the oil.
On my previous Sundowner, and many other airplanes, the fix is to
install an external plate over the oil cooler, usually right in
the air inlets next to the prop. On my Sundowner, it was a
metal plate with a hole the size of a quarter drilled in the
center. But that's primitive stuff and non-adjustable if
you're flying x/c somewhere. You have to stop and remove the plate
when you get into warmer temps. That's not as practical when
you fly a plane that can go 1000 miles on a tank, when running at
a very economical LOP cruise.
On my RV-10, I did this same modification. It's one that you
want to do a little carefully, but is also very simple at the same
The root of the install is a throttle valve sold by TCW
Tech. They sell it with an electronic
controller and actuator, which is fine, but I don't have
nearly the trust for electronics as I do mechanical devices.
The issue is, if anything were to malfunction, especially on a hot
day, you're looking at the inability to lower your oil
temperatures. If the throttle plate becomes loose and flaps
shut, or if the actuator quits, or anything. Some of these
problems are potential issues regardless of electronic or
mechanical control. Either way, do this mod at your own
risk, and take every care to ensure it's foolproof.
For my install, I just bought the Butterfly Valve from TCW Tech,
and then a couple of different components to connect it to a
regular push-pull cable. I had to buy a different "B" nut to
attach to the cable than thte stuff that's provided with the
butterfly valve, but it was simple.
Here are the parts I got from Aircraft Spruce:
05-16210 Cable "B" Nut Throttle 222-1 (About $12)
05-14072A-740 Control 72" Black Knob
There may have been a misc. cotter pin and washer too, but I think
that was about it. You just stick the B-Nut in the arm, and
the cable gets attached to the B-Nut and swivels freely. I
also used a scrap of 1.5x1.5" aluminum angle to make a bracket for
the cable to attach under the panel. It's attached above the
bottom edge of the panel with a nutplate on the aluminum angle, so
it's easy to remove. You do have to make sure to run the push-pull
cable thru the bracket before you install the cable
permanently. The cable then routes back to the same
cable passthrough used by the Throttle/Mixture cables, and I made
sure to do gentle bends in the cable and not let it rub on
anything else that could cause wear. I used some Adel claps
I had on hand (order those if you need them) to attach them to the
engine mounts, keeping the smooth curves. You want to mount
an Adel clamp very close to the butterfly valve as well. The
butterfly valve is just held on by a coupe of pop rivets, and the
air intake SCAT tube gets shortened just a bit for the reduced
Once it's all mounted up, make sure that when you push the black
knob all the way in, the valve is COMPLETELY vertical and full
open. Then pull it out until it stops and it should be
mostly closed. Repeat this MANY times to enure you have no
binding. Initially my adel clamp wasn't close enough to the
butterfly valve, and when I pushed the cable in after having it
all the way closed, the flexibility in the cable caused it to bow
sharply on the throttle valve end, and not move the arm.
That would have been very bad, meaning I was full closed on the
throttle valve, and pushing it open only opened it a crack.
That's why I make it a point to say to mount the Adel clamp close
to the butterfly valve. This keeps it stiffer so it can't bow out
of place, and ensures it will fully open. Test it over and
over and over until you know it can't fail, and make sure to lock
down the allen screw on the B-Nut. Then you're done.
I have found that in the winter of 2018/2019, I actually flew
around most of the time with the valve almost completely closed,
just to keep my temps in the 185-195 range. It never got too
hot. And, when coming in for a landing to park the plane, I
kept it fully shut to ensure that the oil wouldn't cool down too
much before I got the plane in the hangar.
It's very controllable while flying x/c as well. You can
easily raise and lower the temps slightly by small adjustments.
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