How do you diagnose turbocharger failure?

[Ulysse]

The POH gives a checklist to follow in case of suspected or diagnosed turbocharger failure.

How do you know? How do you differentiate from a power loss (total or partial) due to other issues ?

[rbp]

one way to tell is that MP will drop 1" / 1,000' of altitude from sea level of 30". so if you'are at 5500', your MP will be about 30 - 5.5 = 24.5"  

hopefully you don't hear any grinding or shredding

[kortopates]

Actually due to the overhead of the turbo, the loss of MAP is going to even bigger than @rbp example above by an 1-2". But your FF & pressure will be fine showing its not a fuel pump issue. But what's even more important to recognize is that with the loss of MAP the mixture is going to be way too rich and you'll have to lean the mixture to get power back and in the process see the EGTs come back up - leaning by EGT. Although its possible to figure things out without it, a good engine monitor is really helpful in recognizing what's going on quickly so you can restore power to some degree. The other main turbo power losses are due to fuel where the monitor comes in again to tell you what to do.

Many of the turbo failures I see, and I see quite a few, were actually preventable if the pilot noticed his declining oil pressure before the turbo seized. One nice if you will with a turbo is its actually the sacrificial part that fails first due to declining oil pressure saving the rest of the engine - if the pilot pulls back power at that point and glides it in to an airport assuming you have the altitude.   

[N201MKTurbo]

I’ve never had one fail. Well, I have found defects and fixed them before they failed. 
I have a friend who builds turbo systems for race cars. I asked him how to tell if a turbo is failing. He said they start making that whirling sound. I’ve never heard the whirling sound, but if you do, you should start heading down.

[Fly Boomer]

3 hours ago, M20Doc said:

Remove the air filter housing from the compressor of the turbocharger, turn the compressor shaft and see if it turns freely with no binding.  
 
If that’s good cap the outlet oil line on the wastegate to the controller. Usually a number 6 line.  With a regulated pressure source connected to the small line on the wastegate, slowly increase the pressure while observing the wastegate, which should be slowly closing.  If it doesn’t move freely fix the wastegate first.  

If it moving freely, reconnect the oil supply line to the wastegate, leaving the out let capped.  Start the engine, when oil pressure comes up the wastegate should fully close, now as you advance the throttle the turbocharger should come up to speed, increasing the manifold pressure.  Remember the only thing controlling manifold pressure is your brain and your hand on the throttle.  You don’t need to go to red line manifold pressure to see that it’s working.  

When pressurizing the waste gate, are you pushing air?  What pressure?

[Fly Boomer]

1 hour ago, M20Doc said:

I use my cylinder compression tester.

So, that's about 80 PSI on the wastegate?

[aviatoreb]

There is something missed on this thread so far regarding diagnosing a turbo charger failure in flight.  I learned this the scary way - I had a turbo charger failure in flight!

If you are at altitude where the turbo charger is making pressure well above ambient pressure - which is usually - then your engine will likely be too rich if the charger fails and this will cause the engine to turn off.  I.e., I was in cruise at 16.5k running 30'' 2200 which is 18gph.  Without the turbo - the pressure is so low inside the cylinders that 18gph is waaaaay too rich and it causes the engine to flood and shut off. So then it was very obvious something was wrong.  I didn't figure out what until I had landed.  There was also smoke because the turbo had started burning oil in the last minutes.  So I assumed I had a fire and didn't correctly diagnose a turbo failure - a restart would have required a much leaner mixture to match the percent power of running without turbo MP at 16.5k.  I think there is also a danger of a fuel fire with that much fuel pumping into a dead but hot engine?  In any case, in my case I made a successful on airport landing, dead stick as there is plenty of glide range at that altitude.  So I learned a lot that day....

[mike_elliott]

Paul Kortopates gave the inflight symptom that happens, and as he says, you have to catch it (oil pressure should be part of your scan VFR or IFR), reduce power and land.

[exM20K]

9 hours ago, mike_elliott said:

Paul Kortopates gave the inflight symptom that happens, and as he says, you have to catch it (oil pressure should be part of your scan VFR or IFR), reduce power and land.

What is the mechanism by which a failing turbo creates lower oil pressure?

[exM20K]

Gary Main sent me these two articles on turbo inspection some time ago.

Bearing Housing to Turbine Housing Clearance-Maint Tip #11.pdf Low Boost #2-Maint Tip #4.pdf

[carusoam]

Great input so far…

let’s invite @Yooper Rocketman to the turbo conversation…

There is also a method for looking for turbo wear as that can lead to issues later down the line…

 

+1 for knowing the engine’s rich state, and the restart procedure to follow…. This is a tough one to get any practice on before you have an actual turbo failure.

There may be an altitude to be below before a restart can be done… check the POH for that…

If there is a restart altitude… below the mountain tops you are flying over…. A good pre-flight of the turbo system may be a good idea…

Thanks to EB for sharing his first hand experience and sushi story that goes with it…  

NA PP thoughts only, not a TC’d PP…

Best regards,

-a-

[kortopates]

57 minutes ago, exM20K said:

What is the mechanism by which a failing turbo creates lower oil pressure?

Mostly the other way around, the declining oil pressure often first does in the turbo; especially when the oil pump starts to cavitate. But a common cause of the declining oil pressure is actually the turbo seal going bad such that the oil is being pumped overboard out the exhaust when it happens on the turbine side (most common). Sometimes its pumped into induction on the compressor side - but the latter will get your attention sooner since the oily induction air will affect combustion once it makes it way to a cylinder.  

[Yooper Rocketman]

Sorry @carusoam for the late response.  I haven't been on this forum for a bit.  Just completed my Rocket Annual and have been on three other time consuming projects ( I typo-ed that last word the first time as Propjects, isn't that ironic? ).

This was my last Turbo Failure  The first page has the initial details.  For shorter reading go to the end of page 2 and all of page 3 for the turbo work.

As Paul @kortopates said, good maintenance should find a turbo going bad most of the time.  

Tom

[Yooper Rocketman]

Just FYI, my first symptom was declining MP, just an inch or two, for which I pushed the throttle in and restored MP to normal cruise.  A minute or two later, it had declined again and throttle restored it. Now I was beginning to think WTH?  I reviewed all engine parameters and everything else was still normal, except I could see the throttle was all the way in.  I told Steve (my Co-pilot, best friend, and A&P) that something wasn't right.  He questioned my like why do your think that?  I didn't get my answer to him when the turbo impeller must have been scraping much worse and we got an instantaneous drop in MP and RPM.

Inspect your turbos closely at every Annual Inspection, especially when you start getting over 600-700 hours.  I've had two fail around 1,000 hours, and have heard the same from several other turbo owners.

Tom

 

[A64Pilot]

Turbo’s “Go” almost always because of the center section bearing is worn beyond limits, too much clearance in that bearing most often causes the intake impeller to hit the housing, the exhaust turbine has more clearance and usually doesn’t hit. But besides that very often but not always this excess clearance and resulting shaft wobble takes out the oil seal, that’s why your losing oil. But the intake compressor wheel contacting the housing is why you loose boost, it’s either slowed  way down or stopped.

So what causes the center section bearing to wear out? Very often it’s from inadequate cool down that causes the oil in the hot center section to form coke after a hot shutdown, this coke is carbon of course which is very abrasive and that’s why the turbo manufacturers are so adamant about proper cool down. EGT does NOT indicate turbo center section temperature, so a low EGT doesn’t mean a cool turbo, low EGT’s and good oil flow and time will cool a turbo though, it takes all three.

[jlunseth]

Wow. I haven’t had a lick of trouble with my turbo since replacing it shortly after I bought the aircraft. That was 1650 ago. I am getting a new one (new engine) so hope it is as durable as the last turbo. I do get it checked regularly. Just one thing, the slow loss of MP is a symptom that exactly matches induction icing. I would close the intake door as the first thing to check, then if that does not do it, sounds like the turbo itself is the next concern.