M

morganjp

Well Known Member
I have an RV6A that I have been flying for 2 years. It has a persistant slow oil leak that only shows up after at least a half hour of flight at high RPM. In other words enough time to spread the oil dye all over the engine. It will lose about 1 qt every 5 hours. It doesn't affect the performance but I am really tired of wiping off the belly. The leak is only on the right side of the engine and is mostly on the top front and rear baffles. It collects on top of carb heat box. Also I have oil coming out on the right side of the aircraft where the upper and lower cowl are joined,

Engine Lycoming O360-A3A carburated

This is where it isn't.

1, crank seal replaced and is dry.
2. oil sump gasket replaced
3. oil filler tube gasket replaced
4. no oil coming from breather tube.
5. cylinder cover gaskets all replaced

If anyone else has experienced this and has a possible anser then I would love to hear from you.

Merry Christmas;

John Morgan
 
I am not an engine expert so use caution. Perhaps it is coming from the case seal (lengthwise). I saw one engine where a poor seal around a case bolt internally showed up outside.

Perhaps you should clean the engine then run it just a few minutes on the ground and use an UV light to try to find the source.

I don't recall the cylinder base to case seal method but that may be work checking. Obviously any bolt or mating surface needs to be considered suspect until you find the leak.
 
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Big leaks like that are usually relatively easy to find, its the small ones that are tough. Clean and dry the engine thoroughly, ground run it for 5 to 10 minutes or until nice and warm then inspect. Shouldn't be that difficult to locate leaking that much.
 
that's a really big leak

I know you think it's all a leak but IMHO if your were to pour a quart of oil over your airplane you will have oil dripping everywhere.

Are you sure you're not seeing a very slight leak and are burning or throwing a bunch of oil.

I speak from experience. I have chrome cylinders and use a quart every 5 hours. I have minimal signs of oil leakage and have talked with Lycoming, Barrett's, and several other reputable engine builders and they all told me I'm in the middle of the pack for oil consumption for chrome cylinders in my time frame.

Just a thought, but I think if you were leaking that much oil it would be everywhere.
 
Have you checked the cylinder drain back tubes? Sometimes those return hoses and clamps get old and brittle, or the clamps get loose.
 
I have tried the engine clean and ground run for 10 min and the leak does not show up under uv light.
All the drain tubes have been clecked numerous times.
 
John,

I've been chasing that same leak for almost 10 years now. Mine uses a quart every 8-10 hours or so and I figure most of it ends up on the belly. What a pain.

But, I've more or less given up on chasing it. Clearly, the leak is smarter than I am.

That said, when you solve it, post something in this space. I'll be watching.
 
morganjp said:
I have tried the engine clean and ground run for 10 min and the leak does not show up under uv light.
All the drain tubes have been clecked numerous times.
Click to expand...

John, you didn't say, but is it a CS prop? If so, this kind of leak can be the 90? fitting on the nose of the case for the stainless prop oil line. It will only leak during flight when the oil pressure for prop control is the highest. This is one of the hardest leaks to detect but one of the easiest to fix. If you do have a CS prop, let me know and I can give you the steps I took to find and fix my leak. If not, disregard! ;)
 
"O" rings?

I had a through bolt behind #2 that would actually blow bubbles after we shut the engine down! You could sit there and watch the little bubbles grow and pop for about 10 minutes after shut down. Each bubble would produce about 1/20 of a full size drop of oil. This equaled about a quart every 5 hrs. What to do short of splitting the case and installing new "O" rings? Our solution is to wash the belly more often. To expensive to split.
 
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