Oil Cooler Throttle Valve

Added 4/10/2019

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 time.

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 distance.

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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