Just wanted to get an opinion on air oil separators. I was thinking I would like to put one on my 73 180 so that I could run about 7 quarts of oil instead of 6 with a greasy belly. I talked to an old grey haired mechanic who told me that they are actually bad for an engine because it does not allow the acids and moisture to breathe out of the engine instead it sends them right back into the engine. Let me know what you guys think about the pro's and con's of an air oil separator and which one you like.
You'll get a lot of disagreement on the benefits of air/oil seperators.
I have an M-20 that came with my Warrior and like the clean belly. I can run 7.5 qts. and not have any messy oil all over my plane. I use av blend and do oil changes at 25 hours tach. (about 30 hobbs) and burn maybe 1/2 quart (usually less) in the process. Oil is still a deep honey color when changed. I too had researched these because I too heard some say bad things about them and was considering removing mine. Upon further investigation, I've kept it.
No problems.
The air/oil sperator is there to......well, seperate air and oil, allowing air (and moisture) to escape as it normally would and recirculate oil back to the engine (oil that would recirculate anyway once you passed the level of blow out (frequently 6-7 quarts)). My belly will have a moisture stream on it's left side belly, but that wipes off easily. Condensed moisure the evaporates from the oil after flight rises to the top of the case where it MAY cause rust/corrosion on the cam and lifters, but the cure is to fly the airplane regularly. If flown regularly, an air/oil seperator isn't going to raise your risk of moisture related internal case problems and you'll have a cleaner belly. A friend whose used a seperator for over 1000 hours just had his engine (O-360) torn down for overhaul (at TBO) and found no case issues. That "old timer" has listened to too many wives tales. Operation and care will have a greater effect on engine condition than just the presence of an air/oil seperator. One additional thing I've started doing after most flights is remove the dipstick for a little while during the cool down period to assist in moisture removal. It's advocated by a experienced PA-28 mechanic I know who maintains an FBO's 4 Cherokees. With or without a seperator this might help some and cant hurt as long as your careful about not letting anything fall down the tube.
That being said, buying one to just keep your belly clean may or may not be worthwhile depending on you paint. An engine that sees reasonable regular use and recieves acceptable care will not be at increased risk for interanl case problems from seperators.
Edited 1 time(s). Last edit at 04/20/2008 02:10PM by 28161.
Hey Brad, Sounds as if the old gray haired mech was having senior moments. As was mentioned above, a separator doesn't inhibit moisture evaporation. It only gives the oil that is suspended in the crankcase vapor time to drop out of suspension and be returned to the sump. As long as the engine is warmed up and flown long enough for moisture to evaporate, it will happen with or without a separator. I like and use an Airwolf/Walker unit on my plane (PA28-235). They are more expensive and more complicated to install, if You don't install them according to directions they won't work at all. They are fairly large and because of that, are hard to use with a lot of 6 cylinder and turbo apps. That being said, if You have the room, they are probably the better unit available and have certainly been developed over the longest period of time. (They have been used by Beechcraft for decades)
We have a M-20 and DO NOT LIKE IT. We have spent a good amount of money having it reinstalled in multiple configurations with no success. We still cannot run with 8 quarts in our 74 Arrow.
If we had it to do all over again, we would probably install and Air Wolf, which 'appears' to be a better design (and, of course, it costs more than 2x as much). We are getting out engine overhauled this August, and the M-20 will probably come off for good.
Something that I've tried on the O-200 on the J3 I fly might be feasible for Cherokees as well. Cost was about $5.
Pull the 90 degree breather elbow from the crankcase after marking a location on it that will result in the outlet pointing up and aft instead of straight down (say, at about the 10:30 position instead of the 6:00 position). Install a section of 1/2 inch copper tubing into the engine side of the elbow, extending about 2 3/4 inches to the midline of the crankcase on the O-200 (I don't know what the midline distance is on the O-320 and O-360). Silver solder the copper pipe in place in the breather elbow inlet. Do not block or obstruct the 90 degree bend in the elbow. Also, install a safety screw into the side of the elbow and pipe if desired. Cut the inboard end of the copper pipe at a slight angle so that the top side sticks slightly further inboard than the bottom side. slightly bend the top lip down a bit, to form a 'duck bill' that will provide a drip point for oil, and will also help prevent oil spray from entering the pipe. Reinstall elbow and safety. Run outlet pipe from the breather elbow outlet up and over the top of the crankcase, aftward along the crankcase, and then down the firewall. Install the whistle slot in the outlet pipe below the level of the mags, but still high enough in the engine compartment to assure that the slot will remain above freezing temperatures. This essentially stops the oil leakage from the O-200 (it is very similar to the oil breather elbow used in the Cessna 150 Aerobat). Don't know if the crankcase innards in the Lycoming are suitable to allow its use -- but, if they are, it will really help reduce oil spillage, and it is both dirt cheap and simple. Would require a 337 of course.
JimC
I have the Air-Wolf sep, and love it. Keeps the belly clean, and avoids a lot of nasty cleaning work. It also seems to keep the oil level up, although for some reason I've not figured out, once the oil gets past a certain number of hours, the level seems to want to keep dropping. The AW is lot bigger than the M20, and can be a pain to fit and to get tuned properly, although I had no problems on the latter. Re the stories about them hurting engine life, I don't think there's any evidence beyond a bit of speculative theory.
28161 said something must be up. I wish I could get to the bottom of the M-20 story too. They wouldn't be able to keep selling them if they didn't work for at least some of the people that buy them but I had one that was given to me because it didn't work for the original owner. It didn't work for me and I gave it away also, the third owner gave it away and the 4th owner loves it. That pretty much rules out a defective unit and Unlike the walker/airwolf there is little or no way to install it incorectly. Something must be up!
Hey Sac,
Didn't You have quite a bit of trouble with Your seperator at first, and did You come to any conclusion about what may have been wrong about the initial installation that was causing the problem? (I've heard that swinging the dead chicken over Your head in a clockwise direction as veiwed from above, rather than from Your point of view can cause unsatisfactory results, especialy if done any time other than during a full moon)
