Well, I thought that I had this put to bed. However, I talked to Tom Swearengen at TS flightiness and he challenged me to find a hose routing that for the oil cooler that didn't require an angled fitting on each end due to potential frustrations with getting them clocked right during manufacture. Plus the idea that less angled fittings lead to better flow.

So, I've been looking at every online picture I could find, photos from Darwin Barrie and Stephan Christopher, Vans prints for the RV7 and RV14, pretty much any resource I could find.

I also burned through about 20' of hose from the el cheapo Amazon hose kit that I've been using for mocking this up.

Long story short; I found 3 solutions that will work.

Solution 1

Routes both lines fwd and down from the cooler, sweeping inboard to the engine. There are 90s coming off the cooler and 45s on the matching hose ends. The other ends are just straight.

Solution 2

Same fittings, but shorter hoses. The inbd fitting goes between the dynafocal mount and the fuel pump. The outboard 45 is clocked more or less horizontally inboard and loops aft of the fuel pump.

Both of these will work, but cause the area infront of the cooler and behind the dynafocal to get pretty busy with oil and fuel lines plus mixture cable and potentially the 2awg starter wire running through that general vicinity.

Option 3 is what I've settled on.

Mount the cooler upside down with 90's coming off both ports, then hoses with simple straight ends sweeping inboard and up to the engine.

I've heard forever that you shouldn't mount an oil cooler upside down because it can trap air inside. Heck, I may even have learned that in A&P school, it's been so long ago I don't honestly remember.

I started looking at this with a more critical eye and reasoned that oil at 100 psi seems like it should purge any air bubbles out of there, so I started questioning if there was any truth this concept. I also discovered that the Showplanes mount that I didn't buy definitely mounts the cooler upside down.

Anyway, I mentioned in on VAF and somebody else said that same thing, so I certainly didn't dream it. It's one of those things that everybody repeats, but nobody seems to be able to definitively be able top back it up with data.

I reached out to Tom once more and asked the question, to which he replied that orientation didn't matter and that any air that was n there would be pushed out by the oil no matter what orientation of the ports. Before he responded, I also reached out to Pacific Aero, on their tech support email with the following:

Good Morning- I'm currently in the process of installing a 13 row oil cooler P/N 8000215 in an experimental airplane with a Lycoming IO390 engine. Oil is supplied to the cooler via -8 hoses and standard AN fittings.

Does it matter which way I orient this cooler? I've always heard that you shouldn't mount them with the ports down because of the potential for air entrapment. However, there is at least one company (Showplanes) that sells a remote oil cooler mounting kit that intentionally mounts this cooler with both ports pointing down.

I ask the question because in my installation it would make hose routing much easier to be able to point the Ports down, but I don't want to impact cooling if that will result in a big air bubble trapped in there.

I appreciate your thoughts on the matter and can be reached via email at genevashortts@gmail.com or via phone 480-440-8817

Best regards,

Terry Shortt

This was on a Saturday, but even so, I had this email response within 6 hours;

Terry,
Your question is very common and equally as common as the myth that aviation oil coolers trap air.

Aviation oil coolers do not trap air because like there is an air fin on the outside of the oil cooler there in an oil fin on the inside.
The purpose of the fin structure is multiple but to include increasing surface area, breaking up flows for increased heat transfer and ensuring even pressure drop across both sides of the oil cooler.
With that, everything flows in the direction of least resistance. So, air will not get trapped because oil will push air rather than oil because it is less resistant to being pushed out of the oil cooler over oil.

I edited the above a couple times while trying not to write a book.
Hopefully it is at least a little bit clearer than mud!
Please advise if you have any questions.

Thank You, Skid Saurenman

Pacific Oil Cooler Service Inc.
1677 Curtiss Ct.
La Verne CA. 91750
Ph. 909-593-8400
Fax 909-593-8499
www.oilcoolers.com

Aero-Classics Heat Transfer Products Inc.
1677 Curtiss Ct.
La Verne CA. 91750
Ph. 909-596-1630
Fax 909-596-1753
www.aero-classics.com

Based on all that, I mocked up the upside down cooler option and the result appears to offer the least potential for conflict with other stuff, as well as eliminating all angle fittings on the hoses. As mocked up in the attached photos, there are 90s on both cooler ports, a 45 on the oil pressure side coming off the engine, and a straight fitting on the oil return to the engine.

Not only did this option eliminate angles hose fittings, but the hoses also got shorter. The outboard cooler port to engine return is approx. 24" and the inboard cooler port to engine pressure supply is about 15". Both of them have nice big radii and enough slack to allow for engine wiggle.

Once I have the rest of my hose runs finalized I'm going to order the whole FWF set from Tom all at once so these will stay in mockup stage for a while.

Feels good to find a relatively elegant solution, but even better to have this put to bed so I can move on to something else!