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Old 03-17-2021, 12:10 PM
Kupde Kupde is offline
Join Date: May 2016
Location: Tampa,Fl
Posts: 44
Default Annoying oil leak

I have a small oil leak from the standard Lycoming IO540 D4A5 in my RV-10. I have about 425 hours on the engine and it probably started about 100 hours ago. I add 1 quart of oil about every 15 hours so not a safety concern but the leak is annoying and gets on all the stuff under the engine. I tightened the oil drain back hoses but it still continues. No evidence from rocker covers. Any thoughts on those with similar issues and were able to find the location? Difficult to find source since the air movement just moves the oil around and on all the stuff on the bottom of the engine. All thought appreciated

Carson City
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Old 03-17-2021, 01:49 PM
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MacCool MacCool is offline
Join Date: Aug 2020
Location: central Minnesota
Posts: 536

I have a small leak at the base of the dipstick tube. Mostly just causes a little mess, doesn't affect oil consumption. My A&P told me that such a leak is common in Lycomings.
RV-9A, 2011, bought flying
IFR certified
AFS 5400/3500, G5, 430W, some other stuff
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Old 03-17-2021, 01:59 PM
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Auburntsts Auburntsts is online now
Join Date: Jan 2005
Location: Tampa, FL
Posts: 2,959

Iím in the same boat. I few times I thought Iíd discovered the source only to be proven wrong. The tight quarters behind the 540 in the RV-10 and the cowl arrangement doesnít lend itself to easy troubleshooting. Kinda given up on it and resigned myself to living with it until such time that a clear cut smoking gun materializes.
Todd "I drink and know things" Stovall
RV-10 N728TT - Flying!
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Old 03-17-2021, 03:16 PM
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bjdecker bjdecker is offline
Join Date: Jun 2005
Location: Georgetown, TX
Posts: 646

In the case of the leak from the base of the oil dipstick tube, replace the stock paper gasket with a neoprene seal. RG-72059 for the 4 bangers ( I'm not sure about the -540 equivalent.
Brian Decker
Retired Firmware Guy and Airplane Builder

2020 RV-14 QB -- Under construction - Tailcone & Empennage Complete.
2018 RV-7 QB -- Built, Flying
2007 RV-7 QB -- Built, Drowned, Resurrected and flying
1998 RV-8 QB -- Started, Sold
1986 Mooney 205SE
1980 Mooney 231

Aided and abetted building a number of other RV's.
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Old 03-17-2021, 03:43 PM
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f1rocket f1rocket is offline
Join Date: Jan 2005
Location: Martinsville, IN
Posts: 2,336

Just something to check, look at where the end of your crankcase vent is situated. If you are pressurizing your crankcase through the breather tube, you will force oil out of various locations on the accessory case.
Randy Pflanzer
Greenwood, IN
Paid through 2043!
Lund fishing Boat, 2017, GONE FISHING
RV-12 - Completed 2014, Sold
427 Shelby Cobra - Completed 2012, Sold
F1 EVO - partially completed, Sold
F1 Rocket - Completed 2005, Sold
RV-7A - Partially completed, Sold
RV-6 - Completed 2000, Sold
Long-EZ - Completed 1987, Sold

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Old 03-17-2021, 07:31 PM
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Ironflight Ironflight is offline
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Join Date: Jan 2005
Location: Dayton, NV
Posts: 12,610

We published an article about the usual spots that leak in a Lyc in Kitplanes last year - if you’re in to chasing down your leak, you might have a look....

Paul F. Dye
Editor at Large - KITPLANES Magazine
RV-8 - N188PD - "Valkyrie"
RV-6 (By Marriage) - N164MS - "Mikey"
RV-3B - N13PL - "Tsamsiyu"
A&P, EAA Tech Counselor/Flight Advisor
Dayton Valley Airpark (A34)
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Old 03-17-2021, 08:45 PM
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RV8Squaz RV8Squaz is offline
Join Date: Feb 2006
Location: Senoia, Georgia
Posts: 849

Paul's article is very thorough. I would just like to add that once you've determined the general area of the leak, one way to pinpoint the exact source is to use the developer (powder) from a dye penetrant kit. Clean the engine as described, spray the developer in the general area, go fly (10 minute flight in many cases is sufficient. For a larger leak, a trip around the pattern may do the trick. And for very large leaks, a brief ground run may do), and finally un-cowl. Any leak will leave an unmistakable trail in the powder.

Some people have had luck with adding a dye to the oil and using a black light to identify the leak.

In either case, it is imperative to start with a CLEAN engine. You may have to rinse and repeat several times. It's not easy and it's a very frustrating process: clean, spray developer, cowl, fly, un-cowl, look, and repeat. But like he said, start with the easy stuff first.

Good luck!
Jerry Esquenazi
RV-8 N84JE
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Old 03-18-2021, 05:02 AM
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blueflyer blueflyer is online now
Join Date: Nov 2008
Location: Shreveport, LA
Posts: 1,050
Default UV flashlight

I found that a UV flashlight from harbor freight ($8) will make the fresh leaky oil glow green. Nothing added to the oil to make it glow. I was surprised how well it shows the fresh leaky oil. Super easy.

Last edited by blueflyer : 03-18-2021 at 05:10 AM.
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Old 03-18-2021, 06:21 AM
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rv8ch rv8ch is offline
Join Date: Feb 2005
Location: LSGY
Posts: 3,755

Originally Posted by Ironflight View Post
We published an article about the usual spots that leak in a Lyc in Kitplanes last year - if youíre in to chasing down your leak, you might have a look....

Very good article! And excellent material for future articles - like how to fix each one of those!

About cleaning the engine...
One tip which might be common knowledge to everyone is that if you have a large, strong hemostat, clamp a rag on the end to wipe things done in the engine compartment. It helps getting into those places that are hard to reach with your hands.
Mickey Coggins
"Hello, world!"
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Old 03-18-2021, 08:48 AM
Kupde Kupde is offline
Join Date: May 2016
Location: Tampa,Fl
Posts: 44

Thanks everyone for the replies. Iíll start with the article and see what I find.

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