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252 Encore oil puddle under exhaust


larryb

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Hello:

     I've had my Encore about 6 months. Yesterday I found a small puddle, about 3" dia under the exhaust. There was oil inside the exhaust. I think this has happened one time a few weeks ago, but at the time I thought it was spilled oil from a recent oil change. I asked my mechanic, he thought leaky check valves most likely but also possible problem with scavenger pump.

     While looking around on-line I came across this article. It made me wonder if there was an operational aspect to this issue. I typically pull up to the hanger and then add power to do a 90 degree turn to prepare for pushing straight back into the hanger. If I shut down immediately after this power application, would I be preventing the scavenger pump from pulling the oil out of the turbo and lines? Has anybody else noticed this with their turbo motors?

     Thoughts?

Thanks, Larry

http://www.knr-inc.com/shoptalk-articles/25-shoptalk/21-201012-flying-a-360

quote from above article:
The inlet check valve opens when there is oil pressure and at a higher pressure than the outlet check valve. At idle (low oil pressure) the outlet valve will be open allowing the scavenge pump to draw all the oil from the inlet valve out into the scavenge pump and back into the engine. This is one of the reasons why you should always allow the turbocharger to spin down and cool off at idle for four minutes after landing. This gives the scavenge pump enough time to draw all the oil out of the lines. Assuming the valves are not leaking, the turbocharger will not fill back up with oil. 

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I thought the scavenger pump pulled from the block and pressurized the lines to the turbo. The idling allows for more cool oil to circulate through the turbo and reduce the temperature.  The check valve (which needs to be installed with the hinge at the top I think) prevents oil from draining down the hose back into the turbo. 

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I would be concerned about that.  I understand the theory about the scavanger pump, but I have never done a spool down and my turbo now has 1100 flawless hours on it.  The question I have is how the oil is getting into your exhaust, even if the scavenger pump theory is correct?  You should not have any.  My turbo has always been bone dry.  I think you have a leak in the turbo, which is definitely not a good thing.

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Sounds like a seal may need looking after...

The only way oil would get into the exhaust pipe would be a seal on the hot side...(?)

Are you seeing any unusual oil usage numbers?

When the turbo is hot, small drops of oil may be exiting the exhaust system, less noticed.  After things cool, a few drops of oil end up on the floor.

what do the logs say about turbo OH or having seals replaced?

PP thoughts only, I don't even have a turbo...

Best regards,

-a-

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On 11/12/2017 at 7:32 AM, jetdriven said:

The turbo is coolest at touchdown and rollout.  Remember it's been at nearly idle for 2-3 minutes at that point with airflow through the cowl.  Idling after that point heats it up again. 

The turbocharger cool down is for cooling the bearings in the turbocharger via oil flow, not the turbocharger housing which is air cooled.  This cool down is applicable to all kinds of turbochargers, not just those for aviation, especially those that have been rapidly spinning for a period of time. 

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The turbo doesn't have absolute seals. If the bearings fill with oil it will pass through the seals.

Your problem is most likely with one of your check valves. They are there to keep oil from draining out of the lines into the turbo and leaking out all over the ground. I would take them both off the plane and take them apart, clean them and inspect them. That may be all they need. If you find broken springs, hinge pins or seals you will have to replace them.

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43 minutes ago, carqwik said:

The turbocharger cool down is for cooling the bearings in the turbocharger via oil flow, not the turbocharger housing which is air cooled.  This cool down is applicable to all kinds of turbochargers, not just those for aviation, especially those that have been rapidly spinning for a period of time. 

And APS has instrumented an aircraft turbo and what they discovered is the whole thing was coolest at touchdown. Exhaust heat then heats it all back up again. The oil may cool he bearings (which are pressed into the CHRA) but  exhaust heats up the whole thing more than the oil cools it. 

This stuff has been beat to death and hashed all the way out on Beech Talk. They just discuss things like this at a higher level than they do here. 

https://www.beechtalk.com/forums/viewtopic.php?f=3&t=136187&hilit=Turbo+cooldown

 

 

F7C55483-09C3-4E84-8AAD-B1EB8D2D08BA.png

Edited by jetdriven
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  We've been down this road before and I think that APS has done a fantastic job putting some OWTs to rest.  However, for folks to put a blanket statement out there that APS has sensored an engine and by doing so they've proven that my Mooney's turbo is coolest at touchdown and I should just shut it down when I get to the chocks without them knowing what it takes to get to the chocks is somewhat unreasonable.  I joined 50+ other Mooneys in the caravan to Osh this year and by the time we taxied to parking (through the grass) my tit was almost 1200df and oil temp was well above normal cruise temps, I have the JPI data to prove it.  I idled until temps were where I wanted them.  There was a poster on the BT turbo cooldown thread (referenced above) that said they will not allow anyone back for B2osh that doesn't shut down there engine immediately and disregard cooling their turbo, I can only assume he owns a turbo rebuilding company cause that is simply insanity in my opinion.  I am absolutely not doubting what APS proved, I am only suggesting that there may be extenuating circumstances that may put some turbos in a bad situation prior to shutdown if their science is taken as a blanket solution.  Giving folks a better way to determine what factors lead to coking of the shaft bearing and other things that lead to turbo failure and how to recognize them may be a better avenue to getting some folks on board with the science.

 

  I have a lot of experience with a lot of different turbocharger applications and I can manage my own system as I see fit, I understand this,  I will shut down when CHTs, EGTs, TIT and oil temperature have stabilized or are headed in the direction that I want them headed in, if they are there when I arrived at the chocks then I'll shut down, if they are not then I will run the engine in a certain configuration as long as necessary to get them there, even turn into the wind if need be.

 

  I think the APS course is a great tool and I support it, I just have a difference of opinion on how they state this solution, or how folks that have listened to their explanation are regurgitating it.

 

Ron

 

 

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Do you always taxi for 20 minutes at 1700 RPM through soft grass and up hills? I think that is an extreme outlier with regards to taxi after landing before you can shut it down.  And of course it’s going to get hot. Mine got hot, too. But that’s once per year for me. 

Wouldn’t you agree that most flights end in a 1-3 minute taxi at low power? And if so, that’s your 4 minutes of idling, if you go back to the point 3 miles out where you put the gear down and pull the throttle back to a low value. 

If you have instrumented data, other than the outlier OSH taxi, that shows  idling on the ramp before shutdown cools the turbo that conflicts with the APS instrumented data, I think we would all love to see it.  

 

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@jetdriven,

 

  Yes, agree that the Osh procedure is an outlier and I used it as such to point out that there are situations that go in the face of what people are stating APS says is gospel.  Everyone is saying that the turbo (housing and bearing) are coolest at touchdown, which I completely agree with, but no one seems to think about what it takes to get to the chocks.  I taxi for approximately 2 minutes at my home field to get to my hanger.  I taxi between 1000-1200 rpm because it keeps a charge on the battery and my POH says at least 1000 rpm, also leaned aggressively on the ground (which adds heat).  I will send you any of over 50 flights worth of data that shows the oil temp, CHTs, EGTs, TIT rising after touch down during taxi, thats whats supposed to happen according to APS and everyone thats quoting them, and it does.  My point is not that APS isn't correct in their statement its that none of us make it a regular habit to shut down at the point where they say its the coolest, so give people a bit more information on what to look for to put them in the best state before they pull the mixture, that's all.  And they may do this, I've never been to their course, plan on going, just haven't been, but no one is saying anything other than we should shut down immediately upon touch down cause that's when its the coolest.

 

  My procedure is to taxi as stated above, get to the hanger and watch the TIT, when it starts falling and the oil temperature starts falling I move the mixture to full rich throttle to lowest idle wait 10-15 seconds while I watch TIT plummet and then pull the mixture.  That's my process, beat it up if you like, but I'm looking for these things to trend in the right direction, most importantly (to me) is the oil temperature.  I'm not trying to argue with any one and I apologize if I'm coming off that way, I just don't see the blanket statement fitting in most of my situations.

 

Ron

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From Garrett (now Honeywell) that makes turbochargers:

https://www.turbobygarrett.com/turbobygarrett/faq

Q. Do I really need the cool down procedure on my turbo?
A. The need for a cool down procedure depends on how hard the turbo and engine is used, and whether or not the turbo is water-cooled. All Garrett turbochargers must pass a heat soak test and the introduction of water-cooling has virtually eliminated the need for a cool down procedure. Garrett is one of the few turbocharger manufactures that subjects their turbos to several OE qualification tests. When you buy a Garrett turbo you can be sure it's a reliable one!

 

Q. Should I run a Turbo Timer?
A. A turbo timer enables the engine to run at idle for a specified time after the ignition has been turned off. The purpose is to allow the turbo to cool down thus avoiding "coking" ("coking" is burned oil that deposits on surfaces and can lead to blocked passages). The need for a turbo timer depends on how hard the turbo and engine is used. Running at full speed and full load then immediately shutting down (heat soak) can be extremely hard on a turbo. Water-cooling of the turbocharger's center housing has essentially eliminated the need for turbo timers or extended idling periods.
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