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Annoying oil leak

Kupde

Active Member
Patron
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

Kevin
RV-10
Carson City
 
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.
 
I’m in the same boat. I few times I thought I’d discovered the source only to be proven wrong. The tight quarters behind the 540 in the RV-10 and the cowl arrangement doesn’t 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.
 
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.
 
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!
 
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.
 
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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....

https://www.kitplanes.com/leaking-lycs/

Paul
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.
 
Thanks everyone for the replies. I’ll start with the article and see what I find.

Kevin
 
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.

+1

I just went through this process here...

https://vansairforce.net/community/showthread.php?t=191165

I got a small UV flashlight from Batteries Plus and it worked great...most oils glow like a shamrock shake. The key is to clean everything up bone dry (like Paul's article says..surgically clean) and just ground run as flying can cause the oil to go in places not associated with the leak. I had a leaking thru-bolt on the middle main and flying would send the oil as far forward as the alternator mounting pad, so I thought I had a crank seal leaking also.

If the leak is small, then I would try the developer technique as the UV light requires some depth to detect. However, even the smallest drop of oil will show up with UV, as long as there's depth and not just a film.
 

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Usual suspects

One area that seems to be a common leak source is the oil cooler fittings. Seems the clocking never works out correct or more needed perfect. It does not take much of a drip even every couple hours to cause fresh drops to be deposited. (UV flashlight test to find these). A trick I was taught is wrap the fitting with a paper towel and then take duct tape or better yet Gorilla tape and seal up the paper towel. Next oil change unwrap the fitting or fittings and you’ll know if there was a leak there. It’s easy and pretty foolproof. You can do this wrap with a paper towel and then wrap with duct tape to look for leaks anywhere.
 
Same but different

Looks like I’m on the same hunt. Found oil on the bottom of my alternator when replacing the belt. No obvious leaks, but oil is dripping from the alternator just like the starter motor picture from the Kitplanes article. At least the front crankshaft seal is good. I wonder why the belt was slipping:rolleyes:
 

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You need to get a case of spray brake/electronic cleaner. To wash off where you can't see. Do not be cheap with it. Spray like you're trying to kill Yellow Jackets. It will clean any areas you can spray it to and leave them pretty dry.
I just went through this problem with my RV-6A I0-360.
Probably had a half dozen small leaks. I THINK I got them all now. Love the clean belly.
Pull out of hanger, run up, back in fix, out, run up, fix, out, run up, fix.
Gets old pretty fast.
Good luck Art
 
Looks like I’m on the same hunt. Found oil on the bottom of my alternator when replacing the belt. No obvious leaks, but oil is dripping from the alternator just like the starter motor picture from the Kitplanes article. At least the front crankshaft seal is good. I wonder why the belt was slipping:rolleyes:

Is that a little oil I see at the base of the cylinder? Possibly a leak from a stud.

I'm in the same boat right now, trying to identify a super small leak! I get about a drop or two every 2-4 hours.
 
Is there a “best practice” for cleaning the engine? I have a couple seeps I want to track down and trying to get in with just rags and solvent seems quite laborious.

I’ve heard of people using pneumatic spray guns with avgas or solvent of choice. Is this safe for the electronics around the engine?
 
Is there a “best practice” for cleaning the engine? I have a couple seeps I want to track down and trying to get in with just rags and solvent seems quite laborious.

I’ve heard of people using pneumatic spray guns with avgas or solvent of choice. Is this safe for the electronics around the engine?

Traditional engine cleaning is done with Stoddard Solvent or Varsol an a sprayer. For anything you are worried about (mags, electric is, etc), cover with aluminum foil. Interestingly enough, the alternator and stater generally don’t care.....
 
Oil Leaks.

I had the exact same leak-or I thought, that would end up on the alternator. I found that my breather tube was slightly pinched and causing too much backpressure in the engine case. In turn, oil was weeping from the front seal and dropping down on the ALT. Once I fixed the breather, no more oil.
If that isn't the issue, check for cylinder base leaking. It's not uncommon for oil to weep from the baseplate area. The last thing to look for is case cracking around the cylinder bases. Lycomings are known to have these issues and will weep oil out of the cracks when the engine gets hot and up to temp.
 
Second on check breather.

Had a few minor leaks very similar stop when breather that was too close to exhaust trying to do the vaporize trick was given free stream. It stopped both the seaps and dropped consumption to normal- it was in too high a pressure zone.
 
I agree with Paul's article that using a sealant on the case half or accessory case is not like to solve the problem. I had a leak at the accessory case gasket that I fixed with Permatex spray sealant. I didn't think this was likely to flow into the leak area so I cleaned the area well, removed the dip stick and attached my shop vacuum to it. I figured if a slight pressure caused the leak then a vacuum might help pull the spray sealant in. This work for this leak.
 
I had one in the early hours. It was maddening because we would lose same amount of oil regardless of time of engine run. Just enough for a messy cowl and a few drops to end up on nose pant. Turns out on the forward face of the engine on the Captain's side there is a small Allen head journal plug that when cold would feel tight and when hot would feel tight but in transition between hot and cold would loosen up just enough to leak. Apparently it was the dissimilar metals warming at different rates that was the issue. Some loc-tite and another quarter-turn and the problem was gone never to return.
 
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I had one in the early hours. It was maddening because we would lose same amount of oil regardless of time of engine run. Just enough for a messy cowl and a few drops to end up on nose pant. Turns out on the forward face of the engine on the Captain's side there is a Allen head journal plug that when cold would feel tight and when hot would feel tight but in transition between hot and cold would loosen up just enough to leak. Apparently it was the dissimilar metals warming at different rates that was the issue. Some loc-tite and another quarter-turn and the problem was gone never to return.
 
AntiSplat air/oil separator?

I installed the AntiSplat air/ oil separator with the breather tube installed into the exhaust tube.
This is not a fix for a leak but definitely cures areas of light seepage which seem to be common on Lycs.
The AntiSplat sytsem draws a bit of a vacuum on the crankcase and helps keep the engine dry and the oil where it is supposed to be.
My 540 is dry as a fart and as an added benefit the belly of my 10 is clean as a whistle.
Just another option to consider.
 
Found some leaks

I went back to the hangar today to look for leaks. I did find oil seeping past the oil drain lines at the hose clamps. I was surprised to find too many of the worm gear hose clamps loose. Those we’re tightened and I will go fly for a while and check again during the oil change in a few weeks.

There was some seepage around a few cylinder studs, but nothing really fresh. The oil vent line was open too, but there was more oil than usual dripping on the exhaust. I wonder if there is any chance that dripping could blow towards the front of the cowl with the right conditions. Seems unlikely.
 
I installed the AntiSplat air/ oil separator with the breather tube installed into the exhaust tube.
This is not a fix for a leak but definitely cures areas of light seepage which seem to be common on Lycs.
The AntiSplat sytsem draws a bit of a vacuum on the crankcase and helps keep the engine dry and the oil where it is supposed to be.
My 540 is dry as a fart and as an added benefit the belly of my 10 is clean as a whistle.
Just another option to consider.

Did you weld the nipple to your exhaust? What filler rod did you use?

I have been sitting on doing this for a couple of years, with other more pressing projects. The oil on new paint is more pushing this one to the top. This would declutter my air exit too.
 
I went back to the hangar today to look for leaks. I did find oil seeping past the oil drain lines at the hose clamps. I was surprised to find too many of the worm gear hose clamps loose. Those we’re tightened and I will go fly for a while and check again during the oil change in a few weeks.
My experience as well. Those clamps get tightened at every annual, but there's a point where the rubber hardens and even a thorough tightening won't stop them from leaking a little. I'm only talking a few drips here, but it is annoying.

Replacement is on next year's to-do list.
 
Oil Drips on the Starter

Well I'm chasing the dreaded oil leak, and have read Paul's article. On an -A model it is embarrassing to taxi up to the fuel pump or a friends hangar and have the nose pants drip. Leaks run right down that convenient wick of hinge pin on the fairing.

I have a known leak at the oil sump strainer crush washer, which I will fix at the next oil change, but am baffled at how a drip could go from there to my starter without touching other up-front accessories. Looking at the pictures there are dark drips on the starter but lighter oil on the case split line behind the starter.

I've looked behind the flywheel and checked other "usual suspects", but haven't put a wrench on any case bolts yet. Are there case bolts above/behind the starter, and would this require starter or alternator removal to access them?

P.S. Does the inside of my F.I. servo intake look normal for 100 hours? There is a dirty blue buildup.
 

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Check the breather lines

Any uptick in crankscase pressure will also cause leaks. Today we had a Lycoming IO-540 on an RV-10 that seemed to be leaking in lots of places. I noticed the air oil separator was plumbed into the exhaust. Yes, it also had the bypass valve, but out of curiosity we checked it by doing a compression check. Compressions were a little low on some of the cylinders (low 60's and one at 58), and a couple of plugs were oily, indicating ring blow-by.
It was interesting in that the check valve going into the exhaust from the separator was really humming like a low whistle while doing the compression checks. We pulled off the exhaust adapter and it was plugged tight, with just a litlle tiny hole showing.

So, for those of you who perhaps have a little more blow-by, check those hoses you have plumbed into the exhaust. When they coke up, it can increase the crankcase pressure.

Vic
 

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...We pulled off the exhaust adapter and it was plugged tight, with just a litlle tiny hole showing.

So, for those of you who perhaps have a little more blow-by, check those hoses you have plumbed into the exhaust. When they coke up, it can increase the crankcase pressure.

Any idea how many hours it took for that blockage to form?
 
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