Oil blow by

[Steve Gruber]

Friends, I am blowing oil out of the breather tube at a rate of 2-3 quarts per hour. I read and understand the overfill concepts but I've run 9 quarts forever and just started this issue. Plugs are dry, exhaust is dry, compressions all good.

One member said he found the issue in his wet vac, I asked him for details.
My mechanics said the position of the breather may be causing a negative pressure pulling oil out the top of the engine. ( it wasn't totally bottomed into the cowling opening.)

Any help would be great, it literally is running down the belly and dripping off the tail skid...
Steve

[Randy Johnson]

Steve I had a similar issue happen when I landed at the ICS convention airport two years ago in Savannah.

A good old boy mechanic took my oil/air separator apart and cleaned and adjusted it. He cleaned the engine compartment and belly of aircraft of oil. Works like a dream now. Charged me 20 bucks. Its depressing to see oil everywhere when you dismount and are away from home. This time it was a happy ending.

Wanted to stuff him in the luggage bay and bring him home!

[Steve Gruber]

thanks for the reply, i should note i don't have an air oil separator, just the blow by tube...

[md11flyer]

Steve.
You might want to check the whistle slot in the breather tube. Sometime these get plugged with good intentions.
If the slot is plugged and your tube is somehow in a low pressure area/venturi effect with the airflow, then without this whistle slot to break this suction,
the oil can perhaps be sucked out this way. By the way the whistle slot is designed for a secondary vent in case the vent tube lower down freezes, but in your case maybe
it was also keeping the vent from sucking out your oil.
Just a thought,
Gary

[Steve Gruber]

THANKS gary, the whistle slot is clear, but the tube was previously up about 1/2" from seating into the bottom position in the cowling hole with the protected housing on the outside, we lowered it by loosening the rubber coupling at the top of the shaft and it did not improve the situation....perplexing but we'll figure it out, thanks for the contribution..
steve

[md11flyer]

Steve, Ok then next step might be to raise the tube enough that you can put an empty coke can under it inside the cowl.
Do a run up and check if any oil is in the coke can. If there is no oil go for a flight of 15 mins and check.... that way you can rule out airflow sucking out your oil.
(if you feel comfortable with the not so standard coke can thing)

Gary

[Steve Gruber]

thx again, gary, the premise here is that the tube in the can eliminates the potential draw and the run up is to see if it occurs without the draw being created by the flight pressures, ...i'll give it a shot,

[Clarence Beintema]

Hi Steve,

You might want to check for high internal crankcase pressure. Although Lycoming does not publish a limit, TCM say that the max is 4" H2O or about 90 mph. In the shop we have an old oil cap to which we connect an airspeed indicator. On run up we read the pressure(air speed) high pressure can be caused by high ring blow by which will pump oil over board through the breather. You can have good compression but still have high blow by. Remember that by doubling the airspeed you have to square the pressure, so the higher the pressure the greater the blow by pressure.

Clarence

[Steve Gruber]

clarence, well, that's a cool test...., so let me see if i get this, i just ran it by my mechanic and he understands the suggestion...

-lyc doesn't spec, but if we use cont spec of max 4"w.c. like a propane or nat gas test or the 90mph airspeed through the engine oil filler dipstick cap with a guage on it.....how do i know what rpm to test it at is it the 2000 run up test?

secondly regarding the squaring of pressure for airspeed, how does this apply to the test? or are you just saying if i have higher than limit airspeed through the engine then the amount of pressure is exponentially higher so it really hurts the situation.

lastly, if i am having ring blow by due to unseated rings wouldn't the bottom plugs be wet?

thanks for your help.
steve