Loosing oil in flight

[Janekom]

Asking the engine gurus on behalf of a friend.

RV10 with a standard IO-540 with about 1200 since new.

On his last flight of about four hours it seems that he has lost about 3 quarts of oil. Looking at the stains it seems to have come out of the engine fuel pump overflow tube. Is this possible? Secondly there seems to another stain looking a bit like fuel?

He did remove the cowl and thinks that it could come from the fuel pump.

Your thoughts will be appreciated. Thank you.

 

[Kyle Boatright]

As I understand it, the fuel pump has two diaphragms. One to keep the fuel on the fuel side and one to keep the oil on the oil side. There is a void between the diaphragms. If you see fuel coming from the port that taps into the void, that means the fuel diaphragm has failed. If you see oil out of the port, the oil diaphragm has failed.

So…sounds like a failed diaphragm in the fuel pump.

 

[MacCool]

does he see oil in the fuel when he sumps the gascolator ? Might indicate that both engine-driven fuel pump diaphragms have failed.

 

[airguy]

Time for a new fuel pump.

 

[JonJay]

Good reminder to check the vent for staining as part of your preflight. The failures I have seen all start with a pin hole leak and small amount of staining that progressively worsens.
I am sure there are other more dramatic failures…..

 

[Janekom]

Thank you all for the replies. I will close the loop and report back when we have finished with the repair.

@ Macool - there is no gascolator on an RV10

 

[lr172]

As I understand it, the fuel pump has two diaphragms. One to keep the fuel on the fuel side and one to keep the oil on the oil side. There is a void between the diaphragms. If you see fuel coming from the port that taps into the void, that means the fuel diaphragm has failed. If you see oil out of the port, the oil diaphragm has failed.

So…sounds like a failed diaphragm in the fuel pump.

+1

This is my understanding as well.

 

[Janekom]

Closing the loop

Well the pump has been replaced and the old one dismantled to understand the mode of failure. This is my attempt to close the loop in order for others to learn as well. Amazing how much engine oil was lost here. It could have ended badly.

The first two pictures show the smaller seal / diaphragm in the first section of the pump. The second picture shows where the small seal goes in. The third picture shows the bigger one. Both are clearly broken and perished. The second bigger one is actually the separation between the thin part of the pump and a part that I would like to call the overflow chamber by lack of a suitable name.

In the next picture I have tried to lay out all the parts in a circle clockwise, except for the small stuff and the spring that are in the center.
1 - Small seal that fits around the shaft.
2 - Pump diaphragm on top of the overflow chamber.
3 - Overflow chamber.
4 - Pump diaphragm below the overflow chamber.
5 - Pump section with two valves.
6 - Top seal.
7 - Pump cover.

The last picture is just to point out what I see as the overflow chamber. In summary one can have failure where the tube will spew out fuel AND a failure where it will spew out oil.

 

[Cth6]

Thanks!

Thanks for sharing the detailed analysis. Glad you got it fixed.

 

[rongawer]

Great information Jan - thanks for the detailed follow up!

 

[cactusman]

https://www.lycoming.com/sites/default/files/attachments/SB548A.pdf

SB above probably not applicable to this failure....but I am a big believer in regular replacement/overhaul of mechanical engine driven fuel pumps.

 

[MarkW]

Jan,
When I read the first post a few weeks ago I would have thought the fuel pump was not the problem. I figured the bypass tube hole was just a convenient place for the oil to drain from the cowl area.
Glad you were able to find and fix.
Looks like the one diaphragm has started to shed rubber. Hard to tell from the oily part picture. This would leave rubber parts in the oil pan or worse, fuel system. Can you confirm? I was unaware we could get trash from the fuel pump itself.

I had the same pump fail o the other diaphragm and allowed a fuel leak out the bypass. Got lucky and saw the fuel drip at a refuel stop. Very small leak as I had not even noticed a difference between fuel usage and fuel compute reading.
Be careful out there.

 

[elev666]

Some were else replacement

So after this post I am thinking lots of us will likely want to zero time our mechanical fuel pumps , so I would like to address the Elephant in the room , where is the best place besides Aircraft Spruce or the other Aviation markets to buy these archaic old fuel pumps?

 

[Janekom]

@ Mark - I cannot see that the small pieces of rubber can cause any damage. I am thinking that the positive oil pressure should keep it in the pump. Not sure. As the actual fuel diaphragm on the other side of the chamber was still ok, nothing could get into the fuel section.

 

[Webb]

Did you happen to notice any changes in fuel pressure over time?

 

[Janekom]

I am not the owner- just the AP who has helped him, but no fuel pressure change reported. Note that it is the oil side that has failed.