About air oil separators. Does anyone have an opinion which works better- M20 or Airwolf ?

I have an Airwolf that I bought along with the Airwolf wet vacuum pump. It works extremely well-- there is very little belly oil. About twice a year, I get under the plane in a creeper and use a light spray of WD-40 to remove what little belly grease there is. I have no experience with the M20.
Warren

I had a M20 on my single... total waste... the company is selling snake oil IMHO... the recommended one was undersized and it was all but impossible to mount it "high enough" in order to get the drain back into the sump. Airwolf might be OK... but I wouldn't consider a M20.
Jim

I had Airwolf's on my PA30 until the engines were overhauled last year. Worked fine.

Jay

This is really good info as I was planning to ask the same question. Getting tired of washing off the belly yet unwilling to give up the reliability of a wet pump. To add to the discussion, I believe Beryl D'Shannon has a separator as well. As I understand it, he works primarily with Beech products. (1) Does he have a separator that is STC'd for a 250 Comanche? (2) If so, any reviews on it?
Thanks,
Don Ostergard, ICS 3263 C-FLHV

A recent discussion about oil/air separators suggested that they can interfere with normal engine function. In extreme cold they can "freeze" and and block the crankcase breather thereby pressurizing the crankcase. Aviation Consumer may have an explanation and recommendation. An oil/air sep is suggested when you have a "wet" vacuum pump.

About freezing, I read an article with photos that said sometimes an ice block can form at the last inch or two of the drain tube. By drilling a small hole in the tube a few inches from the end, it will still breathe even though the end is blocked by ice.

I have had personal experience of ice forming at the end of the breather tube. The tube was designed and built with a venting bypass hole partway up the tube to protect against this. However, this bypass hole can only do so much. If the tube is aligned properly, the end of the tube should not freeze up in flight. The larger danger is that condensation from the warm, recently shut down engine will run down the tube. If the ambient temperature is really cold, this condensed water will freeze inside the tube right at the very bottom of the cowl where the cold air can get at it, forming a plug right at the very bottom of the tube. One beastly cold day several years ago I fired up and took off without realizing the need to check the bottom of the tube. Just at rotation speed, (at full power, of course), the crankcase pressure built up enough to blow the front crankshaft seal out of its seat. This in spite of the required bypass hole being in place and open. I made a VERY quick low level pattern and landing. I lost 6 litres of oil in just a very few minutes, much of it covering the windscreen. I always check the bottom of the breather tube now, as part of my walkaround, whenever flying in the winter.
Don Ostergard, ICS 3263 C-FLHV

I should clarify a couple of things regarding my misadventure as described above.
1. It was the main crackcase vent tube that was blocked by ice, not the air/oil separator vent tube.
2. The vent tube was misaligned in such a way that the bottom end protruded excessively below the cowl.
3. I have owned the plane for a bit over 31 years. I had flown it with a misaligned vent tube for about 15 of those years without any negative issues. Since realigning the vent tube, I have never seen any evidence of ice blockage during my preflight inspections.
Still, it never hurts to be vigilant.
Don Ostergard, ICS 3263 C-FLHV
c-flhv@magtech.ca