I'm seeking input on the possible leading causes for an ongoing oil leak at the crankcase breather tube of a Lycoming 0-360 other than just being overfilled, its not that. Co-incident with the ongoing leak is a higher than average oil temperature 190-215, oil pressure is in the normal range.

Not an official mechanic, but having build many different engines over the years have you checked to see if you might have excessive blow by in any cylinder? Have you done a compression test? This pressurizes the case and could cause your problem. Just my unofficial guess.

How about more info in the engine. How many hours since last rebuild? how many hours on the cylinders? How many hours per year? Spin on filter or oil screen? How often are you changing the oil and type of oil? Oil additives? What rpm are you running? CHT's? What is oil usage per flight hour?
DENNY

air/oil separators

Ya lots of scenario's to consider, no two engines are the same. Just wonder if anyone had a similar experience and what their "fix" was.

Sounds like a classic case of blowby from worn or cracked piston ring. Also a classic reason for a good compression check. Fix is pretty self explanatory if that’s the cause.

Halestorm wrote:Sounds like a classic case of blowby from worn or cracked piston ring. Also a classic reason for a good compression check. Fix is pretty self explanatory if that’s the cause.

Agreed, that does seem to be the most logical explanation. It seems a bit early at about 500 hours for a top overhaul following a full overhaul but it's a "new" to me engine. I have no way to know how other's treated it before me !!

Mapleflt wrote:

Halestorm wrote:Sounds like a classic case of blowby from worn or cracked piston ring. Also a classic reason for a good compression check. Fix is pretty self explanatory if that’s the cause.

Agreed, that does seem to be the most logical explanation. It seems a bit early at about 500 hours for a top overhaul following a full overhaul but it's a "new" to me engine. I have no way to know how other's treated it before me !!

This is just another example to me of why I prefer to not pay a premium for a "fresh overhaul" when buying an airplane. I'd rather one close to TBO that I know I'll have to overhaul at some point and pay less for it. That said, my money is on rings either broken or not broken in correctly and jugs are glazed. I'd be doing a compression check and checking the inside of the cylinders out with a borescope. You might get lucky and not need a complete top, just new rings and a hone job.
Has it done it the whole time you've owned the engine, or is it a new problem?

A bad oil cap gasket can cause this, believe it or not. The increased air pressure on the top side of the engine can pressurize the crankcase, causing oil to be blown overboard.

Ross4289 wrote:A bad oil cap gasket can cause this, believe it or not. The increased air pressure on the top side of the engine can pressurize the crankcase, causing oil to be blown overboard.

Thanks, I'll give mine a closer look.