An M-20 Model 300 oil separator was installed on my C180K with a O-470-50 about 5 years ago. Unfortunately, my mechanic and I recently noticed that the separator has small corrosion pits on the bottom surface near the two outlets, which are starting to drip oil ( though the rest of the engine compartment and plane seem to be doing well with respect to corrosion, and the plane has primarily been kept in a hangar). I tried calling and emailing M-20 to talk to them about the issue, but all listed contact info was bad and I'm guessing they are out of business? With that in mind, do folks have a preferred separator that they would recommend as a replacement?

Not sure what an M-20 is, but keeping oil off of the belly isn't rocket science.
Buy an AirWolf or do what most Alaska Aviators do and run your breather into a 1.5 liter jug that doesn't vent anywhere close to the cowl flap area.
The whole secret is keeping the breather tube well away from the cowl exit area.
That area creates a vacuum and actually sucks oil out of your engine.
On my machine, I have the end of the breather tube about six inches from the cowl flap.
Flew my plane to your lovely state and the only problem I had was exhaust on the pod/belly.
If you look at the AirWolf website, they recommend doing just that.
Do some experimenting and let us know what you find.
Kommi, 237, Skytruck….

I see no significant benefit to using an air/oil separator. All you need is a proper crankcase vent tube, with a whistle slot, and you're good to go.

In cold weather air/oil separators may not be your best friend. And, if that thing is corroding, don't you suppose that Its also holding moisture in your engine case, and possibly creating corrosion INSIDE the engine that you can't see?

That's why you have a crankcase vent.....to remove moisture from the engine interior.

Anything that gets in the way of that is bad in my opinion.

MTV

mtv wrote:I see no significant benefit to using an air/oil separator. All you need is a proper crankcase vent tube, with a whistle slot, and you're good to go.

In cold weather air/oil separators may not be your best friend. And, if that thing is corroding, don't you suppose that Its also holding moisture in your engine case, and possibly creating corrosion INSIDE the engine that you can't see?

That's why you have a crankcase vent.....to remove moisture from the engine interior.

Anything that gets in the way of that is bad in my opinion.

MTV

Agree.

Separator discussion. http://www.piperowner.org/forums/topic.html?id=98987

SkyTruck wrote:.....The whole secret is keeping the breather tube well away from the cowl exit area.
That area creates a vacuum and actually sucks oil out of your engine.
On my machine, I have the end of the breather tube about six inches from the cowl flap.….

Please elaborate...does the breather terminate about 6" above the cowl flap? Or 6" laterally somehow?

Mine terminates about six inches above the cowl flap.
If your engine is worn out or you run your engine full of oil, there is no cure for an oily belly.
My engine is certified for 12 quarts but the oily mess subsides if I keep it between 9 and 9 1/2 quarts.
If you look at the installation instructions for an AirWolf Oil separator, they tell you to keep the exit of the breather well away from the cowl exit or cowl flap area.
There are many that run the breather into a plastic water bottle inside the cowling. If the breather tube went to the bottom of the bottle and the bottle was stuffed with something like a pot scrubber (plastic or stainless) it even works better. It gives the oily mist something to condense on before venting out inside the cowl.
Every oil change, change the bottle.

I can sorta see having a breather routed into a collector as described by Sky Truck, although I personally view the breather as an automatic anti-belly-corrosion applicator. (like the computer guys say, "it's not a glitch, it's a feature") I don't get the separators that route the blown-out oil back into the engine via a fitting screwed into the valve covers (or however). When the C-145 engine in my old 170 was high time, it dripped some mucus-colored stuff out of the breather after each flight-- there's no way I wanted that stuff going back into the engine.

hotrod150 wrote:I can sorta see having a breather routed into a collector as described by Sky Truck, although I personally view the breather as an automatic anti-belly-corrosion applicator. (like the computer guys say, "it's not a glitch, it's a feature") I don't get the separators that route the blown-out oil back into the engine via a fitting screwed into the valve covers (or however). When the C-145 engine in my old 170 was high time, it dripped some mucus-colored stuff out of the breather after each flight-- there's no way I wanted that stuff going back into the engine.

That mucus colored stuff is oil with moisture mixed in while hot......and you are right, you DON'T want that stuff poured back into your engine, which was the point of my earlier post.....I don't want any device putting moisture back into the engine.....the purpose of the crankcase vent is to rid the engine case of as much moisture as possible.

If your vent tube is set up right, and as noted by an earlier poster, you don't try to fill the engine to max oil capacity all the time, you really shouldn't get much oil on the belly.

MTV

Visited a test cell engineer at the Lycoming factory, a few years ago, he mentioned gallons of water get pumped through the crankcase during the life of an engine. Best to vent out the blow by.

I believe in a unobstructed breather. My O360 leaves two drops on the ground after a two hour flight. Belly stays pretty clean.

Analogy: run an (5) HP air compressor for (2) HRs check the sump. Then image how much moisture is consumed in a 180 HP engine for (2) hours? The breather is a "replace" for a drainable sump which is impracticable.