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Oil temperature problem solved...finally

Zuldarin

Well Known Member
Let me start with a little background on my engine and why I think I was having oil temperature issues. I have an RV-9A with an IO-360 but its not just any IO-360, its got a few "modifications" that are pertinent to this discussion.

First, the bottom end of the engine is actually from a 200hp angle valve IO-360 which means it has piston oil squirters. This feature squirts oil up against the bottom of the piston which removes heat from the cylinder...hence better CHT control. I rarely if ever have issues with my cylinder head temps getting over 400 degrees.

Second, I have a Superior cold air induction sump. This means I get cooler air into the engine but it also means I have one less heat extraction path for heat in the oil pan.

Third, I have dual P-Mags (electronic ignition) which, as I understand it, means hotter temperatures in the cylinder due to better efficiency and advanced timing. Those hotter temperatures combined with the piston oil squirters means more heat to the oil.

Ok, now on to the story. As you might suspect during my original build I expected to have higher than normal oil temperature from the piston oil squirters, or at least more of a heat load in the oil system so I purchased a SW 10599R oil cooler from DanH hoping it would be enough. I also mounted the oil cooler on the firewall and fed it with 4" scat/ducting.

I've been flying for a few years now and in the summer I have to be very careful with high RPM's. If I keep my RPM above 2400 for more than a few minutes my oil temps get into the 220+ degree range which is much hotter than I am comfortable with. Yes I am aware that Lycoming allows up to 240 degrees but I'm not comfortable with those temps myself. Once I level off and things stabilize I can run anywhere from 185-200 degrees which is acceptable but it does require lower RPM's. High RPM's always mean high oil temps.

That said I decided to try again to resolve the high oil temp temp at high rpm issue so this year when I took the airplane down for the annual condition inspection I decided to make a change to the oil cooler. This time I decided to go with the Airflow systems 2007X 15 row oil cooler...the same one I plan on putting in my RV-10 when its done. That required a bit of work on plenum, baffles, and the oil cooler inlet duct since the oil cooler was about an inch bigger than the original.

I have completed the conversion and I have done a few flight tests including a full throttle 2500 RPM climb from sea level up to 8000' MSL and the results are excellent! I couldn't get my oil temps over 190 on that climb! I'm happy.

I think the hardest part of the process, or at least the most work was involved in creating a new inlet duct for the oil cooler. I am pretty happy with the results so I thought I would show my process in case anybody else out there has a similar issue with this engine configuration. There were more steps than outlined below but for the purpose of this post I think these steps are the most important.

First step was to design the new oil cooler inlet duct. To do this I took a few measurements of the oil cooler and then fired up Solidworks to design a duct that takes a 4" scat hose and converts it to a rectangular shape that fits the oil cooler. Here is the result of that process:

Oil%2BCooler%2Binlet.JPG


Next up was to use my 3D printer to print up the duct. To tell the truth I actually printed up 3 different ducts trying to get the right fit and form. The duct below is the final iteration.

20180605_004834244_iOS.jpg


I added a 3/4" aluminum ring to the inside of the duct to act as a hard point for the hose clamp pressure that will be applied later.

Next up was to use a couple layers of carbon fiber glass cloth, some "poor mans vacuum bagging" and a little peel ply to wrap the 3D printed duct.

20180605_121137835_iOS.jpg


Then, I did a little sanding, a final thin coat of epoxy, and this is the result.

20180608_002327621_iOS.jpg


Then it was simply install and seal.

20180608_210512787_iOS.jpg


And thats it! Using the 3D printer to form the base of the duct was such a huge step forward from the foam I formed with knives and files on my first duct.
 
Very impressive work! You will get a lot less pressure drop with those nice, smooth transitions. I did something similar on my plane, but split the plenum into two 2" inlets - one on either side of the engine mount. (My plane is a little tighter in there.) I made a mold for the plenum out of foam and duct tape, then laid up fiberglass over it. It's not as pretty as yours, but I have plenty of cooling. Actually, in the winter, I blank off one of the 2" ducts.
 
Oooo, I like that! Pretty work.

The printed duct form remains inside the carbon shell? I know nothing about 3D printer materials. What sort of temperatures will it stand?

I think your assumptions regarding configuration and accessories are largely correct, the big factors being squirters, advanced timing, and RPM. Squirters are obvious. The timing advance is just wrong for ROP operations. The often-assumed "hot spark" stuff has nothing to do with it. Way back in the NACA papers on cooling, the big brains identified mass flow as a significant factor, meaning RPM. Pulling RPM from 2700 to 2500 for climb can make a noticeable difference with a constant speed.

One of these days I'll measure heat gain in the intake tracts.

Was the 10599 mounted on the rear baffle, or remote mounted? I was cooling a 390 with it and never got to 220F, but I was using some fancy ducting.
 
Yes the printed shell is actually only about a 1/16th of an inch thick and its melting temperature is about 200' Celsius. I ran a similar configuration last year without the epoxy cover and it held up well even in the summer heat but I wasn't completely comfortable with it. I wanted to add some security and rigidity to this duct so I added 2 layers of carbon fiber. I will keep an eye on it and if I see any indications of melting or other compromise I can always break it up from the inside and remove it completely.

The 10599 was mounted in the same location but the air feed was lower on the back baffle. Part of this project was moving the air inlet up a little higher so that none of the cooling air was going through the #4 cylinder cooling fins.

This is the old location. Notice the back baffle had to be replaced so I could move the outlet flange up about 2".

20180512_172116655_iOS.jpg


And this is the new location. Not a great picture of it but you can see its higher. You can also see a 3D printed inlet ring that I put in there to smooth air flow into the flange. You can also see some of the various changes I was playing with before I decided on this configuration.

20180525_212305902_iOS.jpg


20180519_171239133_iOS.jpg
 
Brilliant work! I had to make a similar mod earlier this year, but didn't quite get it together with the 3D printing workflow. I still get up to 220 on climb on hot days, but always cruise around 185-190. Mine's only a 10-row cooler though. Couldn't fit much else on a -7 without rearranging everything on the firewall.
 
Care to post the solidworks files? There's been some nice work done but everyone wants to keep the files close hold for whatever reason. Post it to thingiverse and I bet many people utilize it. It would be nice to have a repository of parts on there that everyone has made so people don't have to reinvent the wheel each time. It looks nice!
 
On another note...

Is it possible that using the scat corrugated tube is slowing the air down and providing less cooling due to turbulence of the air flow? I wonder if making a smooth tube might help with cooling the oil.

-Marc
 
Is it possible that using the scat corrugated tube is slowing the air down and providing less cooling due to turbulence of the air flow? I wonder if making a smooth tube might help with cooling the oil.

-Marc

I'm sure it would help a little but everything works so well now that I probably wont mess with it much more. I do plan on inserting smaller and smaller inlet rings until I find out how much air is needed to keep the oil cool. Either way it does need some flex in the hose since the oil cooler is rigid mounted on the firewall. You will notice in one of the pictures that I was experimenting with ducted elbows to see if I could get a single straight run of SCAT which would eliminate the rough edges.
 
Care to post the solidworks files? There's been some nice work done but everyone wants to keep the files close hold for whatever reason. Post it to thingiverse and I bet many people utilize it. It would be nice to have a repository of parts on there that everyone has made so people don't have to reinvent the wheel each time. It looks nice!

I have no problem posting the solidworks files. I just created an account and uploaded the file but it says I have to wait 24 hours to make it public.

Keep in mind that this duct most likely will not work for anybody else unless they have their oil cooler mounted in the same location I do with the same angle toward the exit. :)
 
I'm sure it would help a little but everything works so well now that I probably wont mess with it much more. I do plan on inserting smaller and smaller inlet rings until I find out how much air is needed to keep the oil cool. Either way it does need some flex in the hose since the oil cooler is rigid mounted on the firewall. You will notice in one of the pictures that I was experimenting with ducted elbows to see if I could get a single straight run of SCAT which would eliminate the rough edges.

Actually I was thinking of my own higher-than-I'd-like oil temps. If it's a warm day my oil temp is high enough that I might try a smooth tube first. I realize it has to allow for movement of the engine, but I think that could be worked out.

-Marc
 
Very nicely done - I believe I have probably another 5 or so degrees of cooling on my oil available with a better diffuser at the cooler inlet and some better air carrier than the 4" scat, and then maybe I can reduce the mass flow for better CHT cooling. Not that I have any problem with CHT's now, but just chasing efficiency.

On the other hand, I may just crack a beer, and fly it the way it is. :D
 
Darin, did you test fly that (blue) inlet ring on the baffle side? I was always wondering if a curved inlet would work better than the stock "cutout" in the baffle.


Lenny

I'm sure it would help a little but everything works so well now that I probably wont mess with it much more. I do plan on inserting smaller and smaller inlet rings until I find out how much air is needed to keep the oil cool. Either way it does need some flex in the hose since the oil cooler is rigid mounted on the firewall. You will notice in one of the pictures that I was experimenting with ducted elbows to see if I could get a single straight run of SCAT which would eliminate the rough edges.
 
Darin, did you test fly that (blue) inlet ring on the baffle side? I was always wondering if a curved inlet would work better than the stock "cutout" in the baffle.


Lenny

Yes I did Lenny, I can't tell you if it makes much of a difference because I changed so many variables at the same time. If I get some time later this month I will fly it with and without the ring to see if there is any noticeable difference.
 
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