Oil Leak

[Dano"T"]

Hi Folks,

I wrote a thread a few months ago on a pesky oil leak I had on my C-85-8. I had a major overhaul done and had only 20 hrs on the motor and every time I flew it there was oil on the bottom of the cowl. My mechanic told me after we tried a few things that he thought it was due to my keeping the oil sump at 4qts. He said to run her at 3 and see what happens. Have any of you guys had this happen? Is the oil just being pushed out the breather hose? Any info would be appreciated.

Dan Gervae
N44008
N26559

[lktiller]

Re: Oil Leak

don't run the engine at 3qts just to save oil ! Doesn't clean or cool efficiently.
Yes, oil will blow out of the breather pipe.
Search this list for some fixes.
Like a tube to insert in the crankcase that puts the pipe opening out of the splash area.
or, like myself, extend the breather tube out the bottom cowl, cut the end of the tube on a slant facing the wind. Puts some pressure on the tube. Advantage is oil doesn't accumulate in the cowling or on the bottom of the plane.

[Robert Lees]

Re: Oil Leak

Are you sure it's coming out of the breather? The breather should terminate below the level of the lower cowl lip.

Try a search for "whistle hole" or similar, to see possible fixes.

We do run at about 1/2 quart below full, any more and the engine chucks it out anyway. Let the engine tell you where it wants the oil level.

[flyguy]

Re: Oil Leak

An old pilot friend of mine says, "If it doesn't leak somewhere, you may not be getting lubrication everywhere."
Seriously, there is a good article in a recent AOPA magazine with manufacturers input that says:
1.The oil level is ok anywhere between maximum and 1/2 down.
Example given: 4 quarts and 2 quarts. The extra capacity is to ensure that you have enough oil at the end of a long flight.
2. If the oil temperature and pressure are OK you have enough oil.

Just passing on what I read, but I think the article makes good sense. My experience with my 6 quart 85 hp is that it chucks the first two quarts out immediately and then stops consuming oil. I start with 5 quarts and usually run it between 4 and 5 for up to 2 hour flights.

Question: Why would one want to put ANY back pressure on the crankcase blowby scavenging system? I can assure you, from personal experience that the vent being clogged will pressurize the crankcase and cause all kinds of problems including making leaks where there weren't any before.

[jgerard]

Re: Oil Leak

Are you sure it's a 6 qt sump, and not just a 6 qt dipstick? I don't know if it's possible to use the 6 qt dipstick in the 4 qt sump but thought it was worth asking.

Jason
N43643

[lktiller]

Re: Oil Leak

The issue was oil inside the cowling. Placing the end of the breather tube outside the cowling will stop that if the source of oil is the breather. Problem is the end of the tube is then in a low pressure area which will drag oil vapor & droplets out of the crankcase and put them on the bottom of the plane.
Cutting the end of the breather tube does not pressurize the crankcase. Creates no clogs either. Cutting the tube at a angle does eliminate the low pressure at the exit end.
The 'whistle hole' creates another place for the oil to splatter under the cowl unless a high pressure area is located. That's hard to find under the cowl when one figures the cooling air exit is always larger than the entrance.

I also have to question why an oil sump designed to hold four quarts (or six) empties the first 1/2 (or 2) quart(s) more rapidly than the rest of the oil? Unless your OIL PRESSURE is decreasing because of the LACK of oil???

The engine depends on this oil capacity to keep contaminates in suspension until the oil is changed. Less oil means the particles get deposited on parts.
Low oil will not provide necessary cooling on hot days either. Circulates too fast.

I have about 600 hrs on a major. Just completed a 7 hr trip (3.5 each way)(no stops). Added one quart of oil at the end of the 7 hrs to bring quantity back up to full.
No oil under the cowl (except for one small leak beside a pushrod tube). And no oil on the bottom of the plane.

I'm no authority, just passing on my experience and bits of knowledge.

[Robert Lees]

Re: Oil Leak

I also have to question why an oil sump designed to hold four quarts (or six) ....

That is the MAX capacity. As long as the MIN isn't compromised, then there is no harm in running lower than the max.

Rob

[Dano"T"]

Re: Oil Leak

Thanks for all the advice guys, I originally thought the leak was coming from the plate on the front of the motor, but we put a new gasket on that and gooped it up with aviation permatex and The oil was still there after I flew it. Can the oil get pushed up inside the cowling when it exits the breather hose? The breather hose extends just out the back of the bottom cowl. From all the responses I've recieved so far and from what I know about my plane...I don't really think I have a problem. I'll fly her some more and we'll see. I had a J-3 and don't ever remember that engine pushing out oil..but all these old girls have their querks and it sounds like what I'm experiencing is pretty normal.

[jgerard]

Re: Oil Leak

pushrod tubes like to leak oil. check that your baffling has not worn a small hole in one of them also. I found most engines will leak more oil during the last part of the oil change interval because the oil itself has broken down a bit and started to loose some viscosity. Also check your oil sump for cracks.

Jason
N43643