Air/Oil Separator for the 252s

[shawnd]

So after doing some long (for-me) cross countries, I have noticed that there's a lot of fresh oil under my aircraft's belly. The start of the spray pattern makes it pretty clear it's from the vent tube. I am assuming this is a result of oil getting dumped from the air/oil separator likely b/c the separator is unable to circulate and send the oil back to the crankcase quickly enough resulting in overflow out of the drain tube. What are some of the remedies?

1. Clean the air/oil separator?
2. Use forced air to clean the lines?
3. Replace the air/oil separator with a bigger better one?

The IPC indicates part # 620065-501 but the effective/notes indicate its effective through S/N 25-0999. Mine's 1026. Appreciate any feedback.

Merry Christmas everyone!

[carusoam]

Check everything from the installation to the hoses...

Start with pics...

There is some discussions about the sensitivity to installation and how well these systems work... some have no issues at all...

PP thoughts only, not a mechanic...

Best regards,

-a-

[StevenL757]

7 hours ago, shawnd said:

So after doing some long (for-me) cross countries, I have noticed that there's a lot of fresh oil under my aircraft's belly. The start of the spray pattern makes it pretty clear it's from the vent tube. I am assuming this is a result of oil getting dumped from the air/oil separator likely b/c the separator is unable to circulate and send the oil back to the crankcase quickly enough resulting in overflow out of the drain tube. What are some of the remedies?

1. Clean the air/oil separator?
2. Use forced air to clean the lines?
3. Replace the air/oil separator with a bigger better one?

The IPC indicates part # 620065-501 but the effective/notes indicate its effective through S/N 25-0999. Mine's 1026. Appreciate any feedback.

Merry Christmas everyone!

Which model separator are you using...an M20, Airwolf, or another brand?

Your engine could be generating excessive crankcase pressure.  This was evident in a past engine of mine, and when I went with a factory reman in 2014, I opted to do away with the separator altogether.  Once removed, and the engine returned to where it was out of the factory, my crankcase pressure measured 0” with an airspeed indicator, and I opted to just live with having to clean the belly a bit more regularly.

[tmo]

You aren't putting too much oil in the engine? Where "too much" might be well within the dipstick range - some engines dump oil to a certain level they like...

[Bartman]

While my engine was being rebuilt earlier this year I did a lot of preparation work for the installation. One of those items was the Air-Oil separator which came with plane and the 700 hour engine. I flew for another 1250 hours and due to oil leaks I could not say for sure if there was any oil at the crankcase vent tube. After soaking for a few days in mineral spirits I flushed it a few times and a lot of crud and flakes came out. I let it dry for a few days and flushed again with clean mineral spirits and flakes of material came out in the clean mineral spirits. I let it dry in the sun for several days, and when I later tapped it on the table I was surprised at all of the flakes of dried stuff that came out. 
 

I decided not to install the old separator on my newly rebuilt engine. 

Edited December 27, 2020 by Bartman

[shawnd]

On 12/25/2020 at 8:50 PM, StevenL757 said:

Which model separator are you using...an M20, Airwolf, or another brand?

Your engine could be generating excessive crankcase pressure.  This was evident in a past engine of mine, and when I went with a factory reman in 2014, I opted to do away with the separator altogether.  Once removed, and the engine returned to where it was out of the factory, my crankcase pressure measured 0” with an airspeed indicator, and I opted to just live with having to clean the belly a bit more regularly.

Great question @StevenL757 - I initially thought the air/oil separator came with the plane but apparently not for my serial #. I will be opening up the cowling soon to get some work done before the annual so will take a better look and send pictures @carusoam. Unless the MSC decides to take a look as well tomorrow for pre-annual chat if wx permits and I can make it down there.

19 hours ago, tmo said:

You aren't putting too much oil in the engine? Where "too much" might be well within the dipstick range - some engines dump oil to a certain level they like...

Good point here too. When we last did our oil change, we put in 7 qt 20w50 +~12 oz camguard to make it about 8 qts. I know its good to put in about 2/3rds of the allowed range, so that should have been 7 qts total. It's now a quart down, most of which I assume is under the belly. I would like to know the reason behind how an engine gets to a level it likes. Excess crank pressure? But how does the air/oil separator come into play there? If the air/oil separator is successful in doing its job, the oil will be returned right back to the crankcase. The only way for the "excess" oil to get out is to find other orifices.

@Bartman that's scary. Did you get a chance to look into what the flakes were? Oil cruft or metal? One of my suspicions is that the lines need cleaning and isn't allowing oil to freely flow back to the crankcase thereby causing buildup in the separator eventually leading to overflow. 

If the air/oil separator is removed, does the mixture pose a threat to the engine? And a bigger question - should I be worried about the oil mixing with blow by gases?

[carusoam]

Natural oil levels... altitude on T/O and climb.... vs. vent location... vs. MP and blow by... vs. oil level while on the ground...

When your system is clean... all the junk collected in the separator... came out of the oil to begin with... this is why people aren’t enamored with automatically putting it back into the case...

Expect that you still have a vent with your separator... find the device’s model number and check it’s plumbing drawing to see how it technically works...

PP thoughts only, not a mechanic...

Best regards,

-a-

[shawnd]

Will post back when I take the cowling off

[Z W]

Just spent a lot of time and money fixing a similar issue over the last 3-4 months.  Oil (a somewhat concerning amount) was dripping out the front of the cowl onto the front tire after shutdown on our 262.  It could not be replicated on the ground or de-cowled, no leaks were visible.  Apparently the oil can leak from a lot of places, and flight pressures blow it everywhere.  Here is what we did:

1. De-cowl the plane, clean the engine thoroughly, run it up, and check for leaks.  It may not be coming from where you think it is.

2. Clean the oil/air separator and lines.  This should be done at annual but is often missed.

3. Replace the gasket on the oil filler cap.  It was $10.00 from Aircraft Spruce.  A bad gasket can pressurize the case in flight, maybe.  This did not fix our issue but is cheap and easy.  Existing gasket was hard rubber and maybe from 1982.  A Mooney-versed mechanic said many planes are missing the gasket entirely.  The cap now seals up much tighter and feels more secure, if nothing else.

4. Check the oil/air separator lines are in the right places.  There is a backup air exit line designed to prevent pressurization of the case if the main drain line freezes up.  Clogs in the lines or improper routing can supposedly cause the separator to function incorrectly in flight.

5. In our case, the oil was leaking from behind a plate that bolts to the engine and holds the vacuum pump and second alternator.  This is a unique plate for the 252 TSIO-360-MB engine I believe.  It really looked like it was coming out the air/oil separator lines but it wasn't.  It was coming out from the plate, running down the vacuum pump, dripping onto the wastegate, and ending up in the nose / on the front landing gear.  There is a $10.00 seal behind the plate that had failed.  Replacing it fixed the problem.

Before this, our engine would routinely blow oil out down to about 6 quarts.  We ran it down to 5, filled it to 6, which minimized the blowout.  After all of this, it happily holds 8 quarts and does not leak.  Not sure which fix ended up with that result, or if it was a combination of all of the above, but I'm very happy with it.

[kortopates]

17 minutes ago, Zane Williams said:

In our case, the oil was leaking from behind a plate that bolts to the engine and holds the vacuum pump and second alternator.  This is a unique plate for the 252 TSIO-360-MB engine I believe.  It really looked like it was coming out the air/oil separator lines but it wasn't.  It was coming out from the plate, running down the vacuum pump, dripping onto the wastegate, and ending up in the nose / on the front landing gear.  There is a $10.00 seal behind the plate that had failed.  Replacing it fixed the problem.

That's a starter adapter leak. Unfortunately they occur all too easily on a otherwise perfectly working starter adapter. Its a real pain to pull one to fix a leak. The most common leakage is from just behind the alternator pulley. There isn't even a real gasket there either, just silk thread and sealant like on the crankcase. Not at all easy to do, but a good mechanic can fix that without removing the starter adapter despite the very limited room saving a bundle of labor hours. But leaks here should be real obvious following the standard leak troubleshooting method of cleaning the engine off real well and then running the engine for a minute or two at a time to find the source of the leak. 

[shawnd]

This is great. After a few test runs during our last oil change, we noticed oil leaks in the back of the crankcase by the alternator. I think you guys have hit one of the nails on the head. I will have the MSC tackle this during the annual. Always striving for clean engines!

 

But I think my air oil separator also needs some TLC:

 

 

It looks worse than it really is - I measure the oil to be certain. Thank you!

 

[shawnd]

So turns out my air/oil separator is listed in the IPC - helps to look at the right serial # Part # is 620065-503. The actual unit has no marking of any kind. Given its designed for the crankcase, likely needs some good cleaning like @Bartman suggested.

@Zane Williams / @kortopates the highest point of the leak behind the engine seems to be around mid point of the alternator against the crank. I will let the MSC tackle these two. Thanks for the pointer!

BTW - anyone know what the code is for the gray color on the baffle (pictured)?

 

[kortopates]

Not but I'd assume its just a rattle can grey color easily matched.

But the that rear baffling material is no longer effective and looks like its leaking really badly along the top rear where the upper cowling sits. I'd replace it soon.

[shawnd]

Baffles are getting replaced - lets not dig in to that in this thread

I tried a few different colors from the local store but no luck. Was hoping some one had the code which would help. @M20Doc would you know?

[Guest]

2 hours ago, shawnd said:

Baffles are getting replaced - lets not dig in to that in this thread

I tried a few different colors from the local store but no luck. Was hoping some one had the code which would help. @M20Doc would you know?

Not really sure.  Can you take a piece to your local auto parts store for a match?

Clarence

[kortopates]

On 1/12/2021 at 11:19 AM, shawnd said:

Baffles are getting replaced - lets not dig in to that in this thread

I tried a few different colors from the local store but no luck. Was hoping some one had the code which would help. @M20Doc would you know?

No paint codes exist. The factory didn't paint the baffles,  they're only bare aluminum from the factory. That was done by a prior owner/mechanic.

Edited January 14, 2021 by kortopates

[shawnd]

4 hours ago, kortopates said:

No paint codes exist. The factory didn't paint the baffles,  they're only bare aluminum from the factory. That was done by a prior owner/mechanic.

Wow - that's interesting and good to know.  Surprising nonetheless. Took @M20Doc's advice and found a small piece that I could unscrew and take it to a local pro paint shop. They were able to get a perfect match. So picked up the base enamel, high heat hardener and reducer. Time to patch up the baffle Thanks folks!

[carusoam]

Some people go all out when decorating their forever plane...

Guy G. has some fancy color coded fire sleeved oil lines to go with that level of detail.

Bet regards,

-a-

[shawnd]

This is more preventative touch-ups Did get my firesleeve lines inspected and replaced right after I bought the plane, also preventative measure.

[carusoam]

Probably better to say forever plane drivers prefer the shiny stuff.... 

-a-

[Ragsf15e]

On 12/25/2020 at 1:17 PM, shawnd said:

So after doing some long (for-me) cross countries, I have noticed that there's a lot of fresh oil under my aircraft's belly. The start of the spray pattern makes it pretty clear it's from the vent tube. I am assuming this is a result of oil getting dumped from the air/oil separator likely b/c the separator is unable to circulate and send the oil back to the crankcase quickly enough resulting in overflow out of the drain tube. What are some of the remedies?

1. Clean the air/oil separator?
2. Use forced air to clean the lines?
3. Replace the air/oil separator with a bigger better one?

The IPC indicates part # 620065-501 but the effective/notes indicate its effective through S/N 25-0999. Mine's 1026. Appreciate any feedback.

Merry Christmas everyone!

Sorry to ping you on the old topic, but did you ever figure out the oil out the breather or was it the accessory leak you mentioned?  Mine has an air oil separator but blows out what looks like a lot?

[shawnd]

Had the line from the top of the engine flushed along with the air oil separator at Advanced Aircraft. Greg and I discussed replacing with larger oil separator but decided to clean and give it a shot first. 
 

I also limit oil to 6 qts for the engine and refill 1 qt when it goes down to 5. I do the oil measurement after the engine has sat for at least a day, typically more than one day, to let the oil drip down to the sump. Basically keep it as close to 6 qt in the sump as possible. Haven’t had this issue since. 

[Ragsf15e]

1 hour ago, shawnd said:

Had the line from the top of the engine flushed along with the air oil separator at Advanced Aircraft. Greg and I discussed replacing with larger oil separator but decided to clean and give it a shot first. 
 

I also limit oil to 6 qts for the engine and refill 1 qt when it goes down to 5. I do the oil measurement after the engine has sat for at least a day, typically more than one day, to let the oil drip down to the sump. Basically keep it as close to 6 qt in the sump as possible. Haven’t had this issue since. 

Thanks.  Cleaning the separator seems like a reasonable place to start and i plan on keeping the oil right around 6.  It doesn’t seem like it’s using a lot but there’s a good streak down the belly after each flight.

[Pinecone]

I had a similar issue in my 252.   The shop on the field removed the vent line and air/oil separator and flushed them.   No more issue.

My engine will actually run fine at 8 quarts and not blow it out, most times.  Then in one flight, it decides it wants to be at 7.

 

[Ragsf15e]

On 2/27/2025 at 6:22 PM, shawnd said:

Had the line from the top of the engine flushed along with the air oil separator at Advanced Aircraft. Greg and I discussed replacing with larger oil separator but decided to clean and give it a shot first. 
 

I also limit oil to 6 qts for the engine and refill 1 qt when it goes down to 5. I do the oil measurement after the engine has sat for at least a day, typically more than one day, to let the oil drip down to the sump. Basically keep it as close to 6 qt in the sump as possible. Haven’t had this issue since. 

I took a closer look at the separator today (getting ready to help with annual in a couple weeks)... the breather line from the top of the engine comes into the separator, then the main drain at the bottom goes down under the left side to exit below the pilot's feet.  Then there's a smaller line coming out the side of the separator also exiting the bottom of the cowl under the pilots feet.  Is that an alternate drain?  And if so, what is the "separator" doing with the separated oil?  It seems both of it's drains go back out under the cowling?  Or does separated oil go back through the main breather line?