Air/Oil Separator Clogged

[Mike Hemsley]

Just a heads up for those of you that have engines that are developing moisture on the back side of your dip stick caps.  After I cleaned out my air/oil separator, which was clogged with oil/water gunk in the screen, my dipstick cap moisture problem stopped completely.  I rinsed the screen with solvent thoroughly and then used a blow dryer to dry it out.

[Ron Hensley]

Mike,

You're getting there....   I'm surprised that you weren't getting a lot of oil being blown out of the oil/air separator through the breather hose onto the belly of the airplane.  But, in retrospect if you're not doing flights over 20 minutes, it might be able to slowly drain down back into the engine between flights.

I have my own schedule for cleaning the oil/air separator, checking hoses, replacing vacuum inlet filters, oil changes/filters, O-rings for gas caps (mains/tips), etc.  This ensures that I know that these items have been addressed and are good to go.  I then tell the A&P not to bother with them during the annual, and that the maintenance on these items has been logged in the appropriate logbook(s).

If you had gunk in the oil/air separator, then make sure that you either clean or change the drain hose as it most likely will have gunk as well.  I would also check the crankcase breather hose to the oil/air separator to ensure that it doesn't have any gunk build-up.  Make sure that you can blow low pressure air through the oil return hose from the oil/air separator back into the engine.

Regards,
Ron

[Greg Stratz]

Unless you have a wet vacume pump, get rid of that air oil seperator. You have already experienced one of the negatives of them.

[Mike Hemsley]

Greg,

You've got my attention.. What are some of the other problems that you've had with air/oil separators?  Would I get more or less oil out the breather without the air/oil separator?

[Greg Stratz]

Just imagine what can happen if all that gunk freezes up on a real cold day, no oil breather function, crank case presurizes and you blow out a crank case seal in front at the prop.
The very nature of the air oil seperator is that it returns oil to you crank case that would have otherwise went out the breather tube. Guess what else gets returned to your crank case, yup, all that nasty looking moisture.

[Greg Stratz]

Unless you have really bad oil control rings on those pistons, I bet you will see very little oil on the belly between flights.
What's your hours per quart?
Does your oil turn black quickly?

[Ron Hensley]

Just imagine what can happen if all that gunk freezes up on a real cold day, no oil breather function, crank case presurizes and you blow out a crank case seal in front at the prop.
The very nature of the air oil seperator is that it returns oil to you crank case that would have otherwise went out the breather tube. Guess what else gets returned to your crank case, yup, all that nasty looking moisture.

Bonanzas and a lot of other airplanes have been flying with oil/air separators for a really long time now in some really cold places.  I bet the actual cases of documented cases of freezing type failures is pretty darn small.  I believe that if the oil/air separator has been installed and maintained properly that it will work at least as well as a newer system without it.

I don't know why you would have one without a wet pump unless you're trying to address another engine related problem that needs to be addressed anyway.

As to water condensation and/or contaminates being returned to the engine, I'll just say horse pucky on this.  Where is the documented evidence showing it's dangerous for the engine and why has the FAA not acted to address the issue?  OWT!

I have not experienced any moisture, freezing, or contaminated related problems on my airplane equipped with an oil/air separator.  However, it is maintained properly, and I follow a more aggressive schedule than the recommended schedule for oil/filter changes.  The reliability and longevity of my wet pump is a given when compared to dry pumps and electrical systems.  But, my plane and I are old school...

Regards,
Ron

[Greg Stratz]

Just imagine what can happen if all that gunk freezes up on a real cold day, no oil breather function, crank case presurizes and you blow out a crank case seal in front at the prop.
The very nature of the air oil seperator is that it returns oil to you crank case that would have otherwise went out the breather tube. Guess what else gets returned to your crank case, yup, all that nasty looking moisture.

Bonanzas and a lot of other airplanes have been flying with oil/air separators for a really long time now in some really cold places.  I bet the actual cases of documented cases of freezing type failures is pretty darn small.  I believe that if the oil/air separator has been installed and maintained properly that it will work at least as well as a newer system without it.

I don't know why you would have one without a wet pump unless you're trying to address another engine related problem that needs to be addressed anyway.

As to water condensation and/or contaminates being returned to the engine, I'll just say horse pucky on this.  Where is the documented evidence showing it's dangerous for the engine and why has the FAA not acted to address the issue?  OWT!

I have not experienced any moisture, freezing, or contaminated related problems on my airplane equipped with an oil/air separator.  However, it is maintained properly, and I follow a more aggressive schedule than the recommended schedule for oil/filter changes.  The reliability and longevity of my wet pump is a given when compared to dry pumps and electrical systems.  But, my plane and I are old school...

Regards,
Ron

You have one because you have a wet pump, that makes perfect sense.
I was addressing the OP who does not have a wet pump, hope I was clear on that.

[Ron Hensley]

Mike,

Could you please post your model, engine type, and whether or you have a wet or dry vacuum pump please?  I assumed you had a wet pump because of the oil/air separator and your previous posts.

Regards,
Ron

[Lewis Gage]

Air/oil separators (AOS)  that are installed behind the rear baffle of the engine, which most are, are PROBABLY not subject to freezing. The temperature behind the engine runs about 30F higher than the SAT and the crankcase gasses start out quite hot through the system.

On engines that have very long crankcase vent tubes of aluminum (the E engine for one) that are above the engine in SAT, even though the crankcase gasses going out through the vent start out quite hot, must be insulated with fire sleeve or other insulation. In very cold temperatures (maybe -15F or colder) the moisture may freeze in an uninsulated vent line causing very high crankcase pressure and then cause oil to run up the drainback line from the AOS filling the AOS and then running overboard through the AOS discharge line.

In normal prolonged flight the OAS is too hot to act as a condenser and the water vapor contained in the crankcase gasses to condense and run into the crankcase via the AOS drainback line. Yes, if all the flying the airplane does is very short 10 to 20 minute flights the system may not get hot enough to work as it is designed, but that is an owner/pilot problem, not an equipment one. A yearly blow with about 30 to 40 PSI back through the drainback line (remember to remove the oil dipstick cap before blowing) is a good practice to remove any accumulated gunk in the line. Yes, it goes into the crankcase but it is probably a very small amount of junk and will be stopped by the oil filter. Or remove the line and clean it.

High crankcase pressue will defeat the function of an AOS system by burping oil up the drainback line. On a long flight the AOS will fill up and oil will be lost overboard with high crankcase pressure.

Regards,  Lew Gage

[Mike Hemsley]

Thanks for all the replies.. Very helpful.. I haven't noticed much oil coming out of the breather vent tubing, usually only a couple of teaspoons of moisture dripping out of the vent tubing after shutdown.  However, I am trying to determine where all the little oil leaks leaks are originating.  I'm thinking there still is a crankcase venting problem that is causing all these little oil leaks.  One possible reason as mentioned in Lew's book, is there may not be enough of a differential from the crankcase and vent tubing exit pressures causing too much internal engine pressure.  My vent tubing currently ends between the nose gear tunnel and the exhaust pipe but does not extend to the outside airstream.  I'm looking for installation and maintenance paperwork so that I can determine if the installation was done correctly. Thanks.. BTW Ron, I think that I have a wet vacuum pump.. Still trying to figure out the relationship between a wet vacuum pump and air/oil separator.. Thanks for your patience..

[Ron Hensley]

Mike,

I have the Airwolf air/oil separator, so I can't help you with the BDS installation, but I think that the breather hose installation should be about the same.  It took me awhile to properly get the breather hose positioned from my air/oil separator to avoid (a) odors in the cockpit when I shut the cowl flaps, and (b) eliminating any siphoning effect which will cause oil to magically appear on the belly of the airplane.

If you have a Garwin,  Pesco, or Airwolf vacuum pump, then you have a "wet pump".  Basically, this means that the pump uses a little oil from the engine to lubricate the vacuum pump vanes and then expels that oil mist along with the air vacuumed from the instruments into the air/oil separator, along with the crankcase breather air (and moisture).  The air/oil separator then is supposed to separate the air vapors from the oil mist inside the cannister and allow the air vapors and moisture to exit the cannister through the breather tube, and allows the oil condensate to be returned to the engine via the return hose using both gravity and a little pressurization from the cannister.  If you didn't have the air/oil separator doing this job for you, you would end up expelling a lot of your engine oil onto the belly of your plan.

I've attached a picture of where my breather hose from the air/oil separator exits the left cowl flap.  There are also references to this problem in Colvin's book, and the 2009 ABS Reference Library CD.

Regards,
Ron

[Mike Hemsley]

Ron,

Thanks for the picture.. I researched my vacuum pump and I have a dry vacuum pump.  There is no tube that goes to the AOS.  Sounds like I can do without this AOS. Simpler, the better as far as I'm concerned.  I have not noticed any oil ever coming out my AOS vent tube...  Of course, I would be bummed to change back to original and start having oil on the belly from the vent tube..

[Ron Hensley]

Ron,

Thanks for the picture.. I researched my vacuum pump and I have a dry vacuum pump.  There is no tube that goes to the AOS.  Sounds like I can do without this AOS. Simpler, the better as far as I'm concerned.  I have not noticed any oil ever coming out my AOS vent tube...  Of course, I would be bummed to change back to original and start having oil on the belly from the vent tube..

Mike,

I guess that this is good news from a certain perspective.   You may want to give the ABS techs a call to find out if there are any legal or airworthiness issues associated with the removal of the AOS and going to a straight crankcase breather, and what they would recommend for a replacement.

Regards,
Ron

[Lewis Gage]

The original installation on the very early V tails had a straight -10 aluminum tube for the crankcase vent line out the right cowl flap opening and it extended to about 5 inches behind the trailing edge of the cowl flap, more or less at the angle of the exhaust pipe. You will see some early airplanes with a soup can sized can installed horizontally in the line above the engine that had the inlet low in the can and the outlet high. Those served to catch the oil expelled from the engine and it drained back when the engine was shut down.

Later, there were a variety of OAS installed as the BDS/Walker are. If the E engine,wet vacuum pump or not, does not put some oil on the belly through leaks or vent line then there is probably no oil in the engine. It is rare to get one that is totally dry of oil outside the engine. A good investment is a comfortable creeper and a spray bottle filled with mineral spirits paint thinner and a big bundle of terry cloth rags. About every 5 to 20 hours of flying get on the creeper and clean the belly. One good thing about having an oil stream on the belly is it is a wonderful opportunity to study the airflow around all of the bumps and antenna mounted down there.

Regards,  Lew Gage