Oil Leak from Turbo

[Z W]

Arrived at the hangar to a surprise today - a puddle of oil under the end of my exhaust pipe.  Pictures below. Plane last flew about 3 weeks ago for 0.6 hours without issue, has been parked since then.

Have not had to do any maintenance to this turbo in 14 years of ownership. No record in the logbooks of it being worked on since 1988 when it was installed with the engine. So it doesn't owe me anything. Had been considering sending it out for a preventative overhaul anyways. No problems with it except maybe, lately, I've been seeing 35 inches of MP instead of 36 on takeoff  sometimes, and once, in flight, had MP fluctuations of 1-2 inches for about 15 minutes before it quit and went back to normal. I had about convinced myself it was just density altitude/temperature/winds or something. I applied mouse milk to the wastegate and it did not repeat.

TSIO-360-MB engine.

Searching here says it could be a problem with the check valves in the oil lines, which can be inspected/cleaned. The oil lines themselves look a little aged, may see if I can have those replaced/overhauled as well. I plan to have the turbo overhauled. A&P can't come look at it until maybe Monday at the earliest, so I have some time for some internet research.  New V-band clamp is on order. Showing expected in stock 1/13/2025 for the V-band through Air Power. Hope that date is correct. Best I can tell, it should be the new riveted style clamp, part number 670105.

Any other ideas/suggestions while I'm at this?  Thanks in advance.

 

 

 

 

[Fritz1]

Maybe just take the oil lines off and see if that tells you anything, after A&P looked at it probably clean everything and spray suspect area with developer and see if that shows any cracks

[N201MKTurbo]

I would look at the check valves before I would do anything with the turbo. A brand new turbo will do that if the check valves start leaking.

[pkellercfii]

I’ve occasionally had this problem with my TSIO-360-MB as well. Fully agree with the advice to check whether either the oil supply or scavenge valve is leaking by. Sorry to say, but, this could also be just operator error. Turbocharged engines don’t like being idled at very low RPM. Mine doesn’t like idling at less than 1000 RPM. If I idle it at less than 1000 RPM just before shutdown, I get greeted by a mess similar to what you’ve illustrated here at the next flight.

Another possibility is that the scavenge line has come loose and is leaking somewhere between the turbo and the scavenge pump in the starter adapter. If that happens, the scavenge line will leak air INTO the scavenge line, interfering with the turbo oil scavenging, and resulting in a turbo oil leak. I’ve had that problem at the connection between the scavenge line and the starter adapter. I fixed that with a ~$2.00 seal from Spruce. Don’t have the part # or link for it handy. I’m away from home & my laptop which has that info.

Warning: Overhauling a turbo because it’s leaking oil is the wrong thing to do. According to an IA renewal instructor at OSH, the shaft seals in a turbo are intended to keep the exhaust out of the oil, not vice-versa. If your turbo is high time, such as more than 1000, then, maybe, yes, overhaul it since high time turbos have some rather non-benign failure modes, to put it mildly. Don’t overhaul it just for an oil leak. BTDT, fortunately Western Skyways footed the bill for that worthless op.

—Paul Keller

 

 

 

[N201MKTurbo]

The scavenger pump is a positive displacement pump. It slurps up the oil like the last bits of milkshake in the bottom of the glass. It pulls air in through both the turbine and compressor sides of the shaft. The oil pump pushes the oil into the bearings and the scavenger pump slurps it up. 
 

If you idle for a long time, it may not slurp hard enough and the turbo and return lines can fill with oil. The check valves are supposed to keep it from draining back into the turbo. If it drains back into the turbo, it will seep into the turbine and compressor housings.this doesn’t hurt anything, but it will make a big cloud of oil smoke when you start up. It will burn the oil in the turbine housing and the oil in the compressor housing will get sucked into the intake and make oil smoke. Your oil consumption will also increase because on every shutdown you will lose the oil that drains into the turbo. If enough oil drains into the turbo, it will drain out the tail pipe. 
 

If you just kick up the RPMs for a few seconds before shutdown, the scavenger pump will slurp up all that oil.

[Will.iam]

Interesting my 252 idles at 650 RPM and smoothly at 700rpm. I have a long down grade to my hanger so i am idling at 700 or less for at least a few minutes after landing and i have not had my turbo leak after shutdown. With continental recommending running the engine at 700 for a 50 RPM rise check and not mentioning anything about idling at or above 1000 rpm before shutdown to scavenge oil out of the turbo. Just a data point that idling at less than a 1000 rpm prior to shutdown doesn’t mean the turbo will leak. 

[Z W]

Thanks for the thoughts and information. I'll focus on the lines and valves.

The thinking to overhaul the turbo too is based on:

1) I am not confident on when it was last overhauled. According to the logbooks, it was 2,700 hours ago in 1988. The engine got an overhaul a little over 1,400 hours ago in 2004, including the lower end with new bearings and all new cylinders, but the turbo system was not done or if it was there was no log of it. It did not qualify as a legal major overhaul. I have reason to believe some of the previous owners were not all that diligent about logging work done on the plane, though that is not obvious from just reading the logbooks. We have put a little over 1,100 known hours on this turbo.

2) Recent failure to develop full MP on takeoff and occasional MP fluctuations during flight. I'm now wondering if the turbo bearings are going and causing rubbing of the blades occasionally. We have overhauled the turbo controller and wastegate, but not the turbo itself. The MP fluctuations I've seen before, and cured with overhauling the controller and lubricating the wastegate, and the loss of 1 inch on the takeoff roll could just be instrumentation or environment changes, but I'm not feeling confident about it.

Lately I've been subscribing to the idea of overhauling critical components before they fail and scrub a trip and/or leave me stranded somewhere, at best, or create a life threatening safety situation at worst. I'm typing this from a hotel that's halfway through an 8-hour drive I'm making because I canceled the flight due to this leak. I don't want to waste money and am also aware of maintenance induced failures. Hard line to walk.

When I get back I may borescope the turbo and see if I can find any play in the bearings, just to know. But I'm still leaning towards sending it out either way.

[Z W]

Also I've never had this happen from idling before. The plane is properly adjusted to idle at 700 RPM or so. I parked it as normal in my home hangar, using the same power settings and practices. Now that you mention it, I always do give it an RPM boost to finish turning it around to back it into the T-hangar before shutting off the engine, which would naturally run the scavenger pump as suggested.  But something has changed.

[Fly Boomer]

3 hours ago, Z W said:

I don't want to waste money and am also aware of maintenance induced failures. Hard line to walk.

This is what drives a lot of major overhauls -- and it should.  When it makes you uncomfortable, it's time to overhaul/replace regardless of hours.  I subscribe to the Mike Busch theory of "on condition" maintenance, but I also need to feel confidence in the machinery.

[Pinecone]

When I had an instance of high oil consumption, I talked to Main Turbo.

They suggested checking the scavenge pump.  Pull both lines off, remove check valves, put the two lines in a container half full of oil.  Run engine.  Oil level in container should go down (sucking more then supplying).

They said that is a common reason for turbo oil leaks.

[Fly Boomer]

25 minutes ago, Pinecone said:

When I had an instance of high oil consumption, I talked to Main Turbo.

They suggested checking the scavenge pump.  Pull both lines off, remove check valves, put the two lines in a container half full of oil.  Run engine.  Oil level in container should go down (sucking more then supplying).

They said that is a common reason for turbo oil leaks.

The delta between suck and supply was being burned or blown out?

[231MJ]

I had the same leak on my turbo, also the TSIO 360MB engine.  I took off both check valves and cleaned them in mineral spirits.  5 hours of flying and no leak.  I had no other symptoms like oil coming out the exhaust or a lot of oil smoke on startup.  Maybe try the low-cost simple stuff first.  If that does not help, the expensive turbo overhaul is always an option.  

If it is a hose-end leak, this is a link to the del seal.  I have not tried this, but others say they work.  

Del Fitting Seals Aluminum | Aircraft Spruce

[Pinecone]

On 12/29/2024 at 12:31 PM, Fly Boomer said:

The delta between suck and supply was being burned or blown out?

If not enough suck, the supply will push oil through the turbo seals.

[Z W]

Update - looked at it closer with an IA today. Going to remove, clean, and inspect the check valves next week. He says he's seen broken springs in them often when this happens, which requires buying a new check valve assembly since the spring is not available separately. Hopefully not the case here, might get lucky. He said the hoses are the good kind, still flexible, and don't need changing.

After inspecting the turbo, he agrees it makes some sense to send it off to Main Turbo in California. The housing is showing signs of age, and sending it in before failure can lower the overhaul cost, if replacing bearings now keeps it from developing a wobble and destroying the housing and other parts. Going to wait until the new riveted V band clamp arrives, though, so the aircraft won't be grounded once the spot welded one comes off. AirPower still shows it backordered but scheduled to be in stock 1/13/2025.

[Z W]

Well, the check valves cleaned up OK. No broken parts and after cleaning they are not leaking.

However, the A&P discovered the turbo was loose and wobbling where the two halves bolt together. Video below.

I can't figure out how this would have caused the oil leak while parked. Perhaps a dirty check valve and the failing turbo are a coincidence? Regardless, the turbo will be going out for overhaul.

https://drive.google.com/file/d/1-VZ3uV-Wz3wp637t6a4yGIRh2e3x64VV/view?usp=sharing

[Ragsf15e]

On 1/11/2025 at 1:28 PM, Z W said:

Well, the check valves cleaned up OK. No broken parts and after cleaning they are not leaking.

However, the A&P discovered the turbo was loose and wobbling where the two halves bolt together. Video below.

I can't figure out how this would have caused the oil leak while parked. Perhaps a dirty check valve and the failing turbo are a coincidence? Regardless, the turbo will be going out for overhaul.

https://drive.google.com/file/d/1-VZ3uV-Wz3wp637t6a4yGIRh2e3x64VV/view?usp=sharing

After you guys cleaned up the check valves did you continue getting the leak out the exhaust?  Mine is starting to do something similar, but the turbo was OH only 200 hours ago, so I'm pretty sure it's not the turbo.  Something else is letting oil in there while it's parked...

[Z W]

8 minutes ago, Ragsf15e said:

After you guys cleaned up the check valves did you continue getting the leak out the exhaust?  Mine is starting to do something similar, but the turbo was OH only 200 hours ago, so I'm pretty sure it's not the turbo.  Something else is letting oil in there while it's parked...

No. I ended up overhauling the turbo, but because we discovered its housing had worn and gotten loose, not because of the leaking oil.

I'm pretty sure the only way for oil to get into the turbo housing while the plane is parked is through the check valves. 

There is an oil scavenger pump inside the turbo that pumps oil back uphill to the engine. If it is worn or failed, you could see oil pooling in the turbo and coming out the housing or tailpipe. But, according to the guys at Main Turbo, that very rarely happens, and when it does, you have giant clouds of black smoke and lots of oil coming out the tailpipe while the engine is running. It wouldn't make it leak while parked, because while parked, the scavenger pump isn't running anyways.

Here's a picture of my check valves - they are the red pieces held in adele clamps. The brown lines coming out are the oil lines going to the turbo (left side, downhill) and then up to the engine on the right.

[Z W]

Also, here are the relevant portions of M0.

Turbo Oil Check Valve Inspection - From M0.pdf M0 Instructions on Turbo Oil Leak.pdf

[Ragsf15e]

33 minutes ago, Z W said:

Also, here are the relevant portions of M0.

Turbo Oil Check Valve Inspection - From M0.pdf 787.04 kB · 1 download M0 Instructions on Turbo Oil Leak.pdf 229.97 kB · 0 downloads

Thanks.  I see they have those nice instructions for the check valves on the -550s, but I don't think ours are the same (different part numbers) and I think a different type unfortunately.  I think those check valve instructions don't apply to ours.

[Z W]

I did notice it says it's for the -550's, but my check valves look a lot like the ones in the diagram, and you get the idea.

The M0 "troubleshooting" section for oil leaking from the turbo for all engines (8-10.2) references the -550 valve inspection by section number (6-4.21), so there's some reason to consider it as applicable guidance on other engines as well, I would think.

[Ragsf15e]

2 hours ago, Z W said:

I did notice it says it's for the -550's, but my check valves look a lot like the ones in the diagram, and you get the idea.

The M0 "troubleshooting" section for oil leaking from the turbo for all engines (8-10.2) references the -550 valve inspection by section number (6-4.21), so there's some reason to consider it as applicable guidance on other engines as well, I would think.

I think you’re probably right.  I am just trying to put all the information together before approaching my IA about disassembling and cleaning the check valves.  I’d much rather start with cleaning and checking them before I throw ~$1400 to buy a new one!

[M20F-1968]

On 12/27/2024 at 10:33 PM, N201MKTurbo said:

I would look at the check valves before I would do anything with the turbo. A brand new turbo will do that if the check valves start leaking.

The first place to look when a small amount of oil is dripping from the exhaust pipe is the check valve with oil going to turbo.  It is a plunger/spring type assembly.  

John Breda

[Pinecone]

On 4/18/2025 at 12:59 PM, Z W said:

There is an oil scavenger pump inside the turbo that pumps oil back uphill to the engine. If it is worn or failed, you could see oil pooling in the turbo and coming out the housing or tailpipe. But, according to the guys at Main Turbo, that very rarely happens, and when it does, you have giant clouds of black smoke and lots of oil coming out the tailpipe while the engine is running. It wouldn't make it leak while parked, because while parked, the scavenger pump isn't running anyways.

 

When I talked to them about tracking down oil going missing, they recommended a simple test for the scavenge pump.  Pull the lines off the turbo and put both into a jar 1/2 fuel of oil.  Spin the engine.  The oil level in the jar should go down, indicating that the scavenge pump it sucking more oil than the supply line it pumping to the turbo.