Air/Oil (Breather) Separators

ghostrider · Post by **ghostrider** » Wed Jun 01, 2005 11:40 pm

Has anyone tried the M-20 air/oil separator? I saw the ad in Cessna Owner magazine and, if their claims are true, one would not have to clean oil off the belly of one's airplane after every flight. They tout better cooling, etc. The web site is http://www.m-20turbos.com.

Any feedback would be greatly appreciated before I sink $360.00 into this apparatus. FYI--it's fully STC'd and field approval for antique aircraft.

cessna170bdriver · Post by **cessna170bdriver** » Thu Jun 02, 2005 12:03 am

Richard

Check http://www.cessna170.org/OilSeperator/OilSep.html for an article by a 170 association member.

Miles

N2865C · Post by **N2865C** » Thu Jun 02, 2005 1:46 am

I tend to agree with Sacramento Sky Ranch who delicately put it this way.....

""Air/Oil separators are like hooking a line up to your anus and piping it back into your mouth. Excuse the crude analogy but who wants the water, acids and other combustion residuals pumped back into ones engine."

More info here.

http://www.sacskyranch.com/condense.htm

http://www.sacskyranch.com/eng30.htm

jc

cessna170bdriver · Post by **cessna170bdriver** » Thu Jun 02, 2005 3:29 am

Sounds like it would be a good idea to NOT install the air-oil separator on the firewall, but install it per Ken Morrow's article, then maybe insulate it to keep the water and acids in vapor form so they don't return to the engine.

Since I would no more want to plumb my anus to the belly of my airplane than to my mouth, another option to keep the effluent off of the belly would be to plumb the return to a small container and empty it periodically... kinda like a port-a-potty.

Miles

zero.one.victor · Post by **zero.one.victor** » Thu Jun 02, 2005 4:37 am

A guy I know has a 180, on which he has plumbed his anus, oops, I mean his breather to a metal bottle,mounted on the firewall. There is a secondary breather line out of this bottle,routed down & out of the engine compartment. Kinda like the water separator bottle installed in some pitot/static systems. He empties the oil and "effluent" out of the bottle periodically. His belly (of the airplane) stays pretty clean. No paperwork on this one, though, strictly bootleg-- but effective.

Eric

N1478D · Post by **N1478D** » Thu Jun 02, 2005 1:04 pm

There is an excellent multiple page article on oil breather lines in the current issue of LPM. It talks about why some airplane bellies are dirty while others are not so dirty. One thing to check is a clogged oil breather fitting and/or line.

Post by **GAHorn** » Thu Jun 02, 2005 11:14 pm

Air/Oil Separators were originally intended, not for crankcase breathers, but for air-driven gyro/vacuum-pump systems way back when wet vacuum-pumps were the common installation. Those pumps were lubricated with engine oil and would pump considerable amounts of the oil overboard. The air/oil seperators were intended to stop the loss of oil from that action.
Along came "dry" vacuum pumps, and their salesmanship efforts included the wonderful claim that NO air/oil seperators were necessary anymore since the pumps did not spray engine oil overboard.
Subsequently someone came up with the idea to use the air/oil separators to stop wet bellies caused by crankcase breather vents that dont' do their job very well without misting oil overboard.
Here's a significant difference between the two concepts: The crancase breather gases contain lots of by-product contaminates including condensation...while the old wet-pumps did not, as they only used engine oil for lubrication purposes. In other words, crankcase gases are vented to atmosphere for a reason....that being so that piston-ring blow-by doesn't pressurize the crankcase and cause prop seals and such to blow out....causing a really nasty belly! All those crankcase gases have so much contamination/condensation in it that there is little sense in reclaiming it and pouring it back into the crankcase, in my honest opinion. Therefore, I personally do not think it a good idea to install air/oil separators in crankcase breather lines.
If your breather blows too much oil...then you should fix the problem....either the worn rings or the improperly routed/installed breather line. (Some breather lines capture oil which runs down from the upper crankcase interior wall, having been slung up there by the crankshaft, and then the natural air pressure that is within the crankcase helps it along to the outside world. There's a fix for this in repositioning the breather line to avoid downhill slopes, and/or to install a modified "elbow" to prevent the oil from running down the interior walls and into the line. A TCM Service Bulletin addresses this issue on the O-200 engine, which has the same set-up as our O-300s.)

ghostrider · Post by **ghostrider** » Fri Jun 03, 2005 1:36 pm

George,

Thanks once again for your excellent advice, as well as that from other members. You have convinced me that it's not worth the expense and I could probably do as one other did with the intermediate trap. My situation is really not that bad--I was just inquiring since the ad sounded so promising. I will look for the service bulletin from TCM and look into repairing the breather if that is deemed to be appropriate.

What a wealth of knowledge just waiting to be tapped by us neophytes.

zero.one.victor · Post by **zero.one.victor** » Sat Jun 04, 2005 5:04 am

Richard, what oil level do you run in your 170? Most tend to blow out a lot if the oil level is too high. Mine has a spin-on oil filter, so total oil in the system is about a quart higher than indicated by the dipstick. I put in 8 quarts at oil change, which reads about 7 on the dipstick, and add oil when it gets down close to 6 indicated-- I shoot for about 6-1/2 on the dipstick. Any more than 7 quarts indicated & it blows it out thru the breather.

Eric

blueldr · Post by **blueldr** » Mon Jun 06, 2005 3:59 am

If you ever saw the inside of the popular aluminum $275 air/oil separator, you would quickly realise that you could build your own for about five (5) dollars. I have one on my airplane and am very happy with it. I've made them for some of my friends, and they're happy too. I change my oil every twenty five hours and don't worry about recycled contaminents. It definitely reduces the belly oil contamination.

ghostrider · Post by **ghostrider** » Mon Jun 06, 2005 6:14 pm

To respond to Eric's question--I was told that I should run my engine about like you described maintaing around 6-6 1/2 quarts. At oil change, I anticipated putting in 8 quarts. Since I will be doing my first oil change since acquiring the airplane, I don't know what my dipstick will read as yet.

To respond to Bluedr--if you have a successful design that you would pass along, even for compensation, I would be interested in building one for myself. I have read the article that someone mentioned in LPM and I will investigate for blockages and correct piping slope, etc.

What a great group of aviators in the C-170 org. You all have been really helpful.

N170BP · Post by **N170BP** » Mon Jun 06, 2005 6:37 pm

The only time I would put in more than about 6.5 quarts if
I was about to launch on a long cross country (I mean a *long*
one... like where you're going to fly 3+ hours before you stop for
fuel). And on the rare occasion I do that, I just live with the
fact that some oil got dumped onto the belly.

My '54 "likes" about 6 quarts. For most "poke around" flying
(boring holes in the sky), I'll make sure there's 6 to 6.5 quarts
in it when I leave.

blueldr · Post by **blueldr** » Tue Jun 07, 2005 4:06 am

I'm currently flying a stock engined '55 B model. Anything above six quarts in the crankcase is blown off at a rate of about one quart in four hours. A couple of weeks ago I flew from my home base at Jackson, CA, to Johnson Creek Airport at Yellowpine,ID. It's about five hours flying time. I changed the oil and added seven quarts before leaving and was down a quart at J.Ck. On the way home I flew five and a half hours, starting with six quarts, and it was down less than a pint on arrival. My particular engine seems to settle at six quarts.
The extra half hour coming home across the desert due to headwinds was the longest "two hours" you can immagine.
Lest I confuse you, I stop for fuel at Nampa,ID, about one hour south of J.Ck. going each way. ($2.75/gal., 7.0 GPH @ 2600 RPM
with a 50 inch prop.,112 MPH TAS @ 9,500 ft.)