MooneyMark

M20K 252 Oil Consumption

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Hello everybody,

Was wondering if any of you have a clue on the following: our M20K 252 has always used one quart of oil every 5 to 6 hours, but consumption is up lately and I'm guessing it's turbo related. Every cold start leaves a significant greasespot on the tarmac and keeps the hangar door wel lubed too. It doesn't seem to leak excessively when standing still, my guess is most oil gets used right after starting. Flew from Holland to Vienna a few weeks back and during cruise it hardly uses any oil. My mechanic isn't sure what's causing this. I'm not that technical, but I understand he replaced the oil return valves leading to/from the turbo, he suspects that the turbo is flooding with oil that is spat out when started. I can second that. These valves should keep the turbo from flooding with oil. But new valves didn't fix the problem. Our 252 always left some oil on the right nose gear door since we got it in 2000, and the turbo has been replaced once due to that. Neither a new turbo nor valves fixed the issue. My mechanic speculates it could be the scavenge oilpump not doing it's job properly our even addional oil gets forced into the turbo due to excessive crankcasepressure. He suggests to check that pressure. I think this trial and error game could be a costly one and was wondering if any of you have dealt with this?

Kind regards from Holland!

Mark 

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Is the residue in exhaust pipe oily and dark? One thing that can be ruled out easily with a borescope is the condition of the intake valve seals. The intake valve stems should be dry of oil unless you have bad intake valve seals. Leaking seals will allow oil from rocker area to be sucked into cylinder. Easy fix if it’s intake valve seals.

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Thanks for taking the time Peter! Don't think that has been checked, but worn intakevalve seals would also mean oil consumption in cruise, I guess? Oil on the geardoor looks pretty fresh actually. I'll discuss it anyway, one more thing to cross of the list!

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Hello Mark
I had the same problem with my 1986 252. It would blow a lot of oil all over the tarmac and right gear door upon startup. I thought that the turbocharger was the culprit. I called Don Maxwell and he told me that he sees this all the time and that people replace the turbocharger but the actual problem is the check valves. There are two of them and they have to be installed properly. If I recall correctly, The word "hinge" is inscribed on each valve and it needs to be on the top of the valve. Anyway, I had my local mechanic check mine. He took them off, cleaned them and put them back properly. Problem solved Hope this helps.

Steve Stansel
1986 252TSE
N252VA


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Thanks Steve, that's exactly the same problem. The checkvalves? Could they be the returnvalves my mechanic was talking about? It's in the shop right now and they're checking the pistonrings with the boroscope, I've pointed them to the valvestem seals and they'll check that out too.

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I'm not sure if that is what he is talking about. The two check valves are held on with yellow high temp adel clamps. Don Maxwell told me that mechanics get them on incorrectly all the time. They have to be oriented in the proper direction and "hinge" on the top side or you will have just what you described.

Steve


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Hello Mark,

The check valves or return valves are the same item and are a likely cause of the oil issue.  As pointed out they are engraved with "hinge" on one of the flats of the hexagonal nut.  This should be install upward.

Intake valve seals are not visible with a borescope, they are under the rocker cover.  Here the cylinder IPC available on line at tcmlink.com

http://tcmlink.com/ektron_cf_share/partslisting.cfm?engineSpec=TSI0360SB1B&SelectedModel=TSI0360SB&Spec=TSI0360SB1B&SelectedPartName=06

Clarence

Friesian living in Canada

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Thanks Clarence! Frieslân Boppe :D I guess they could see the valve dishes with the boroscope and if they are oiled up we've got our culprit. Because the Mooner hardly takes oil in cruise, I don't believe the seals are worn, but who knows for sure. I've pointed my tech in the direction of the check/returnvalves, I've got a feeling we could be on to something with those. Again, who knows?

All your input is much appreciated! I'll keep you guys/galls posted!

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Nicely stated technical challenge, Mark.

Is that the oil all over the front landing gear door in the picture?

It looks like you are onto the solution...

Turbo oiling systems are pretty complex, including seals that wear, and parts that get funny names like 'scavenger pump'. They even renamed the check valves...

It is difficult to understand everything that is involved.

If a part can be installed two different ways, there is a 50% chance of getting it done incorrectly...

I look forward to your follow-up post describing your success..!

Best regards,

-a-

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Thank you! Yup thats oil (and me in the right seat) Turbo's are pretty straightforward in theory, but to make 'em work they way they should involves quite a bit of engineering (obviously). I'm learning along the way!

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Flew for a little bit last Sunday and she still flings out oil like nothing else. It could be because they tinkered with her and there's still oil left in the turbo, then next time will be better. I hope I can squeeze in some extra flighttime this week and make sure.

Does anybody have a pic of correctly mounted checkvalves?

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I have a 1988 252 with a similar problem.  I get a fair amount of fresh oil through the nose wheel cavity that trails on the belly of the aircraft.  I don't get any oil "blowing" toward one side or the other, but every time I fly the belly gets a fair amount of oil across it.  Could the check/return valves be the problem?  There is no clear indication of the source of this flow from an evaluation of the nacelle area.

I'd sure like to get this solved.  It's not a great deal of flow, but it doesn't take much to soil the entire belly when you fly at 252 speeds!  By the way, I recently flew from Idaho to Florida.  I maintained 190+ ground speed for more than 3 hours at ~10,000 ft.  Burning between 12-12.5 gph.  Got the O2 system ready to be back in service, so I'll push up to the 17,500 range and see what happens up there.

Thanks for any help.

Pascal Budge

N33RK

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Just a small update to tell you there isn't anything to tell you yet. Didn't do any flying this month... Few flights planned but all had to be cancelled due to the lovely Dutch weather...

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Did a couple of flights the last few weeks and I didn't have to add oil yet, but she still lubes the gear door. The pic is from the door after taxiing to the fuelstation. After a flight it's clean.

I suggested to my tech to give Mike Busch a call.

IMG_5919.JPG

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Wow that's not right

have the check valves checked for leakage, as mentioned the hinge must be up, installed in the correct direction and verify the scavenge pump is pumping.  If the check valves leak the turbo will fill with oil after shutdown and on start up you will blow it out. I have never seen a turbo seal do this but if everything above is good the only thing left is the turbo.  Also check the turbo exhaust inlet when you pull the turbo. If the exhaust stack above is wet with oil above follow it.  At high power it would burn the oil and at low power it blows it out on th gear door. 

Jim

Edited by Jim F
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That could be oil being blown out the case vent...

If the engine was started, and the oil mess is only external...one of those hoses in the photo is probably going to the case vent...

is there oil dripping from the Case vent hose?

 

If Yes, there is a way to measure what the proper case pressure should be...

 

Often oil departs the Case vent under ordinary conditions... when the oil level is kept too high.  This, and a combination of attitude...

 

Lyc IO360s are best known for this behavior.  Continental’s, not so much...

What does your oil level indicate, at this time?

PP thoughts only, not a mechanic...

 

Best regards,

-a-

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Probably not case pressure, the exit for blow by is on the left hand side.  It very well be a turbo issue, but don't discount Peter's idea. A friends 231 had worn valve guides on one cylinder and oil was dripping down into the cylinder after shutdown. On startup the oil would blow out. No noticeable excess oil usage in cruise. A bore scope would tell. 

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Although I'm not at all sure, I take it my tech checked proper fitment of the checkvalves. I pointed them in that direction and he also mailed with Mooney concerning this matter, and he said they're okay and fitted correctly. I would just love to pop of the cowling and check it all myself, but I've decided to leave it to the pro's. I am wondering how 'pro' he is though, cuz he billed me one hour labor for swapping the landinglight... This I will do myself next time. 

So assuming the checkvalves are okay and the crankcase pressure is high, but within limits (they check this with an old ASI... never knew!) then that leaves the valvestem seals. Need to check if they did the boroscope.

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@MooneyMark,

 

  If it were valve guides (we don't have valve stem seals that I'm aware of) you would look like an airshow performer at startup with smoke billowing out.  Especially the first start up of the day with a cold engine.   This appears to be raw oil exiting the exhaust, it is probably coming from the turbocharger center section past the shaft seal in the turbine housing.  Now it could be a bad seal or it could be due to the turbo charger filling with oil due to the check valve leaking or a weak scavenger pump or a combination of things upstream.  If your mechanic has a borescope then it should be pretty simple to look into the turbine section of the turbocharger and see if the oil is being fed into it via the exhaust or if its coming from the turbocharger internals.

my .02

Ron

Edited by Marcopolo

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@MooneyMark,

If you get that much oil on your gear door from just taxing back from the fuel pump, the source should be fairly obvious.  If it came out of the exhaust there will still be oil or residue in the tailpipe.  If that is the case you know to look at the Turbo, check valves, and the valve stems as mentioned above (I have not heard of this happening but it makes sense. with that much oil though I would expect some serious plug fowling)

Everyone,

I'm new to turbo ownership, only 60hrs so far.  Checking the exhaust pipe for signs of oil is one of my per-flight items.  If I find any trace my plan is to stay on the ground and sort it out.  Am I being too conservative?  So far there are no signs of my turbo leaking as far as I can tell (I'm sure a small amount can at cruise and would never be detectable). Is it common to find some oil coming from our turbos?

Cheers,

Dan 

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I think you're somewhat conservative. I see this as a nuisance, and although not good, as long as there is enough oil in the sump I'm flying. In my years of ownership she always marked her spot in this way in some degree.

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@DanM20C,

 

  In my turbo experience (150hrs M20K and 1000+hrs in race/street cars) no, there should be ZERO oil making its way past either shaft seal (ceramic or step ring).  Like you, I take a quick fingertip swab of the exhaust pipe at pre-flight as I also check for looseness.  I have built, re-built, destroyed and replaced many a turbo over the years and there should be no oil visible outside of the sealed center housing of the turbocharger.

 

Ron

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@MooneyMark,

 

  We are not sitting behind a radial engine here.  I would not be comfortable with an airplane that "marks its spot" out of the exhaust anymore than a car that does it.  The oil should stay in the engine sans the bit used to help the rings seal to the cylinder walls and gets burned off.   

 

Ron

Edited by Marcopolo

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@Marcopolo,

Thanks, that's what I thought. 

I've been a normally aspirated guy my whole life.  I have heard some turbo horror stories in the past so I'm watching mine like a hawk.  Love flying with it!

Cheers,

Dan

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3 hours ago, MooneyMark said:

Although I'm not at all sure, I take it my tech checked proper fitment of the checkvalves. I pointed them in that direction and he also mailed with Mooney concerning this matter, and he said they're okay and fitted correctly. I would just love to pop of the cowling and check it all myself, but I've decided to leave it to the pro's. I am wondering how 'pro' he is though, cuz he billed me one hour labor for swapping the landinglight... This I will do myself next time. 

So assuming the checkvalves are okay and the crankcase pressure is high, but within limits (they check this with an old ASI... never knew!) then that leaves the valvestem seals. Need to check if they did the boroscope.

Hi MooneyMark,

The check valves can and most likely are leaking.  The check valves stop oil from flowing to the turbo when the engine is off.  If the check valves leak the oil will flow from the engine to the turbo after shutdown and pool.  On startup it will blow out the pooled oil.  So it's not just the hinge location.  Have your mechanic remove the check valves and with the valve arrow pointed up put solvent in the top and wait to see if the solvent leaks through.  That will tell you if they are leaking.  You should always look at the lower cost stuff before moving to the big ticket items.

Jim

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