1 Million Gallons of Oil on m'Belly!

[bkervaski]

Curiosity question...was the cracked elbow a real AN fitting? If not, I missed it on the TC call.

They are blue anodized AN822-8D fittings supplied by Vans. The manufacturer of the oil cooler said we should be using steel fittings. I re-installed new AN822-8Ds per the manual, did not install steel fittings.

In my rush to reply "hairline crack" may have been a hasty choice of words ... I guess it could have just as easily been damaged threads on the compression side but I did not see a thing wrong with this fitting but you can see it leaking when the engine is running ... sure enough, replacing it fixed the problem.

It took two people and three engine runs to find it, they had to get real close and personal as the oil was a tiny jet like spray, got everywhere .. again

Edit: But .. this was after just over 60 hours of flight so whatever happened to it happened suddenly, within 1 flight. I don't know how one of these could fail, has not moved since installed.

[BillL]

Originally Posted by bkervaski

I don't know how one of these could fail, has not moved since installed.

I still don't know exactly where this failure was . . . cooler boss, threads, fitting, hose

Regardless, here is a possible failure example . . . if the steel fitting was installed with 567 sealant and was tight, the NPT creates hoop stresses the thread hub. Oil pressure is not steady, it pulses due to volumetric variance as the pump rotates. This pressure and ripple can add to the tension stresses created by installation. If the NPT installation pushed the boss to near the stress limit, the cycling could have completed the fracture. It would have presented itself suddenly.

[Discus2b]

....steel vs. aluminum...
....manufacture vs. Vans....
I?m surprise no Vans rep has chimed in on the science of all this. How about some clarity on why Vans would go with aluminum fittings against recommended application by the manufacturer.
Should I swap out to steel?

R

[pilotkms]

Just looked this up on the Pacific Oil Cooler site. Articles - Common Oil Cooler Woes > They advise to use steel, with thread lubricant. Only use aluminum as a last resort. (Maybe AOG?)
I installed per their advice. But mine is a 7 - different? Have also heard same advice from more than one A&P.

[Bavafa]

From what I understood to be the reason for the steel, is that the aluminum fitting if not used properly can mess up the thread. A good lubricant is required for a successful installation.

[BillL]

Originally Posted by Bavafa

From what I understood to be the reason for the steel, is that the aluminum fitting if not used properly can mess up the thread. A good lubricant is required for a successful installation.

This topic has been beaten down several times before. As a single data point, I had to remove an aluminum fitting from my oil cooler after it was installed and sat for a few months. It came out without pulling any threads.

BUT It will gall if installed by hand dry though, so it truly is sensitive. I did that too, just lightly threaded it in and got stiff quickly, removed , chased the threads (lightly) and noted never to do that again.

Bill, where exactly was your crack?? The cause could be the fittings in the boss, but also a hose without adequate room to allow the engine to rock generously can break something too.

[bkervaski]

Bill, where exactly was your crack??

I really couldn't tell you ... at the time I didn't care much about digging that deep ... once replaced, problem solved, moved on.

Was obvious though, a single tiny stream of spraying oil, that whole area was soaked in a matter of just a minute or two at idle.

I'm concluding it was the fitting because everything else was replaced first, i.e., oil cooler and the suspect hose.

[Phil]

I had the same issue with an AN fitting going into my remote oil filter mount. For months I tried to get the leak solved and never could do it. Time and time again I?d pull the fittings out and attempt to reseal the threads.

I eventually discovered that the aluminum fitting itself had a micro-crack inside the fitting. Months of frustration ended by simply buying a new fitting and sticking it in the hole.

It came in as a new fitting but it had a crack. It wasn?t visible to the eye but the oil had no problem finding it.

[DanH]

Bill, Phil, those cracked fittings...are you sure they were genuine MIL-spec AN? Look-alikes are called "AN" in every hotrod catalog, and often have the part number, but it doesn't mean they meet the spec. The look-alikes have also been known to sneak into inventory at legit aircraft vendors; ignore the source and check the fitting.

[Phil]

This specific fitting was supplied by Air Wolf with my remote filter setup. There?s a chance they supplied a look-alike, but they do sell certified products so it?s doubtful.

At the end of the day, I can tell you how I got it, and that I got it from a reputable supplier.....But their source supplier is not 100% known.