What's the life time of an air-oil separator? Will it leak?

[THill182]

OK; this is a continuation of my engine saga of apparent excessive oil use here:

Upon further investigation, we now found excessive oil coming out of the air-oil separator of my IO550G (see STC# SA02033AT, http://www.cessna170.org/OilSeperator/OilSep.html#Install). In fact, after 15 hours of flying after my last oil change, I had a black "cake" on my nose gear doors -- which came from the vent of that air-oil separator. Note that I don't see any oil on my hangar floor.

One explanation is that I have excessive blow-by, creating pressure in the engine, which perhaps is overwhelming the air-oil separator? But I am grasping at straws here: Is there another explanation? Maybe the life time of those air-oil separators is limited (mine is 11 years and probably 1300 hours or more old, or so).

Clearly I am blowing oil overboard, but mostly while flying and hot it seems.

What puzzles me is that I had the problem (excessive oil usage, about a quart every 3 to 4 hours), then it went away for no apparent reason for one 35-40 hour oil change cycle, and now it is back.

Does anyone know under what condition this air-oil separator would start blowing stuff overboard, instead of returning the oil to the engine?

Really puzzled by all this -- and obviously trying to avoid experimental top overhauls (all the compressions are pretty good still).

 

 

[Bartman]

I too am very interested in the responses to this question.  My bird has an air oil separator and although I can go about 8 hours on the first quart, all subsequent additions are about 4 hour intervals.  This has been steady for 10 years and about 800 hours and I have investigated leaks several times but never really found a "leak" yet the belly stays covered. I run my IO-360 at 6 quarts, 2500 RPM cruise, and compressions have always been in 70s. I am considering removal of the separator at inspection next month. 

[aaronk25]

I'm guessing you have a m20 brand separator which are more touchy to get to work properly because of the smaller size when compared to the air wolf brand. However a few on this forum have got them to work good.

I think the biggest issue is locating the units exhaust in a location that doesn't have a lot of negative pressure like near a cowl flap but ensuring there is enough negative pressure to evacuate the oily gasses from the engine cowl.

I'd say, as a guess if your truly blowing that much oil out the breather tube for 40 hours then it improves either a ring got stuck then freed up or you were running over 6qts of oil. Try keeping it at 5.5 and see if it improves. I fill to no more than 6 at oil change and add when the mark is at or just under 5qts but I live in MN where temps are low and keeping excess oil in the sump to act as a heat sink during long hot climbs is rare. In fact up here it's normally waiting for enough oil temp to depart . So less is more.


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[aaronk25]

Oh and to answer your questions lifetime should be unlimited.


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[Piloto]

I had an M20 oil separator for 10 years and really happy with it. As others mention it has to be properly installed for good performance. Most important is that the intake has to be above the case vent port. Mine has the oil drain to the bottom side of the #4 valve cover. The exhaust is connected to the original line. There was 1/4" side hole on the line that I plugged. I found that the hole needs to be plugged for optimum performance. The hole is a backup for in case the vent tube is iced. I think this is more of a myth since the vented vapors are at least 100F with no chance for icing. I can fill to 8qts with no belly stains. Oil consumption is about 1qt/9 hours. There is no filters or screens inside M20. It is just two pieces of coaxial pipes inside. It works on the principle of vapor condensation and gravity. The condensed vapors are accumulated on the outside container and later discharged to the engine when is off. If the oil content on the vapor is too high or the trip too long it may exceed the outside container and it may start discharging on the exhaust port. For optimum condensation the M20 must be away from hot spots in the area. The only maintenance on the M20 is flushing it with MEK to keep the drain port clean.

José

Edited November 15, 2016 by Piloto

[jdrake]

I installed a M20 separator on my J about 8 years ago.  It worked well after making several minor adjustments to the line routing and position of the overboard vent.  Fast forward to 2014 when I developed an unexplained leak near the separator.  Upon removal we discovered that some very fine pitting had developed at the base of the unit allowing oil to weep out and down the firewall.  Not exactly sure of the cause <insert argument about concentrating acids, etc here> but replacing the unit has me flying with a nice clean belly.

 

[carusoam]

Question of the day...

Why a separator for an IO550?

unlike the IO360 there isn't any oil being blown overboard at usual or even high oil levels.

Best regards,

-a-

[kmyfm20s]

I removed my M20 separator and found less oil consumption. I was getting a fairly healthy coat of oil on my belly before I removed it. After removal I get a lot less on the belly but get a streak of oil down my gear door after it sits which can be easily wiped off. I removed mostly because I didn't want the corrosive by products going back into the engine, less consumption was a plus.

[THill182]

3 hours ago, kmyfm20s said:

I removed my M20 separator and found less oil consumption. I was getting a fairly healthy coat of oil on my belly before I removed it. After removal I get a lot less on the belly but get a streak of oil down my gear door after it sits which can be easily wiped off. I removed mostly because I didn't want the corrosive by products going back into the engine, less consumption was a plus.

That's interesting, and also to respond to carusoam' s question (why a separator on an IO-550): I put this on a long time ago, when I first got the plane with an engine that had problems, one of those was a lot of blow-by. In retrospect and knowing what I know now, the air-oil separator is not the solution to such problems.

Anyway, I had everything looked over to rule out oil leaks, and also had some of the old & brittle hoses replaced connecting to the separator. I changed the oil, and next I will continue flying at reduced power (55%-60%) to see if I get the reduced oil usage, as I had seen in the oil-change-interval before the current one. If so, then I will go back to 70% power as normal. If oil usage then goes up, then I am pretty sure that it's time for a top overhaul (after roughly almost 1,200 hours -- not great, but not unusual looking at the Ovations for sale). But I still have some hope that maybe changing/cleaning out the hose may make a difference -- probably not.

[carusoam]

My experience also comes from mostly LOP, lower power ops...

I had been a CB for a long time.  Before retiring...  

best regards,

-a-

[carusoam]

GB,

can you clarify...  putting a fire sleeve on the vent line keeps the temp up? To prevent coking?

I would expect the sleeve is insulating the oil in the vent from a heat source nearby, but outside the line.

vents are typically not hot enough to cause coking. Cylinder heads, exhaust valves and exhaust pipes are the usual sources of enough temp to cause coking...

Thanks for helping out with your expertise.

I am only a PP with an IO550 wondering if I should be looking at a similar vent challenge...

Best regards,

-a–

[DonMuncy]

I could easily be wrong, but it would seem odd to me that the air/oil separator would "coke" up. Gunk up, yes, but I would expect you could take one off and with some effort, clean it out. I can't believe they would have a life limit.