Pickling

[Pinecone]

On 10/26/2024 at 7:12 PM, EricJ said:

The idea being, by then it is outside of the engine.

It is not hard to get the engine oil and case above the boiling temp of water while on the ground.   A few minutes of that to assure the water vaporizes and then has a chance to cycle out the vent will decrease the amount of water in the engine if it has been sitting and accumulating water due to condensation.

Running an engine periodically also pumps the oil around to relubricate everything.

There are tradeoffs to everything, though.  YMMV.  You can also leave an engine sit for as long as you wish.    

No, the air in the engine is fully saturated.

And the manufactures state that it takes 30 - 60 minutes to evaporate the water from the oil.   Do you have actual data that says differently?

Also, a LOT of anecdotal info about engines that were severally corroded with ground runs only.  

[MikeOH]

1 hour ago, Pinecone said:

No, the air in the engine is fully saturated.

And the manufactures state that it takes 30 - 60 minutes to evaporate the water from the oil.   Do you have actual data that says differently?

Also, a LOT of anecdotal info about engines that were severally corroded with ground runs only.  

Hmm, on the one hand you want to criticize his argument without 'actual data' but then expect your argument to prevail based on "a LOT of anecdotal info"???

Sorry, not very convincing

[Pinecone]

Did you read any of the links or quotes?

Have you heard of anyone saying they did ground runs and their engine is OK?

Show me ONE good source that says that doing ground runs on a stored plane is a good thing.

[MikeOH]

Yes, I read both.

I haven't heard of anyone saying their engine was ruined by ground running, either.  I'd bet there are people that have had corrosion ruin their engines that they flew!  More hyperbole than logical argument.

I started this discussion because it reeks a lot like the LOP debate.  IIRC, manufacturers (Lycoming/Cont) didn't approve of it and there were countless 'anecdotes' from 'reputable sources', A/Ps, and self-appointed cognoscenti denouncing the practice.

I'm just questioning the conventional wisdom on this.

My contention is that damage from corrosion is due to moisture in the AIR, acids in the oil, and time:

AIR: That's why if you're in Tucson corrosion isn't going to be as big a concern vs. St. Pete.

ACID: Note that one of your cites talks about CHANGING the oil and filter and then flying for an hour.  Why would that be?  Maybe to dilute the remaining acid in the old oil that remains after changing?

TIME: I think that one is kind of obvioius  The longer it sits, regardless of any other factors, the more time oxygen and moisture have to do damage.

Personally, I think the 'moisture in the oil' thing is a bit of a red-herring.  I posit a couple of arguments to support my position:
One, whether you ground run or fly, the oil temp is what it is: somewhere around 180F (per your cites, even 165F is minimally acceptable).  From a 'evaporating' moisture point of view how does the engine 'know' if it is airborne or on the ground for reduction of oil moisture content?  I was always told to avoid prolonged ground runs at even moderate power for fear of overheating the cylinders as airflow is NOT the same as flight.  BUT, that is a DIFFERENT argument completely UNRELATED to 'getting rid of moisture in the oil'.
Two, both of your cites refer to the NEED to examine the desiccation material every 15 days!  If 'moisture in the oil' was the real issue vs. moisture in the AIR, why would this be necessary?  After all you just put fresh, moisture free, oil in the plane as part of the preservation procedure.
A further point is where did the moisture in the oil come from in the first place?  If from combustion then how does running the engine 'drive out the moisture' when running it is creating the moisture in the first place?  Also, note that at the temps we are discussing we are NOT boiling off any water but merely increasing its rate of evaporation.

From the FIRST paragraph of your Continental cite: "There is no practical procedure that will insure corrosion prevention on installed aircraft engines. Susceptibility to corrosion is influenced by geographical location, season and usage. The owner/operator is responsible to recognize the conditions that are conducive to corrosion and take appropriate precautions".
Thus, they address geographic location/season (moisture in the AIR), and usage (TIME).  And, more importantly, with the phrase "there is no practical procedure" pretty clearly acknowledge their own procedure is inherently limited/incomplete/not guaranteed.

A couple of final thoughts for further speculation.

If the moisture in the oil is really responsible for corrosion then there are two possibilities:
One, the moisture 'comes out of the oil' while it is sitting at room temp and becomes "available" for the corrosion process to occur in air.
Two, somehow the moisture in the oil, along with oxygen in the oil, corrode parts that they are coating.
The latter seems unlikely to me as it goes against the 'conventional wisdom' that one of the reasons for Lycoming camshaft corrosion problems is that the cam's 'high position' in the engine facilitates the oil draining off and exposing the cam to oxygen/moisture in the air.

What do you think the ambient humidity in the crank case would be, compared with the outside ambient humidity, three days after flying one hour with 50 hour oil, and with freshly changed oil?

It seems to me that some real science (i.e. controlled experiment) is needed here.  Absent that we are all speculating as that Continental introductory paragraph is hardly compelling evidence that even the manufacturer has this figured out!

[Pinecone]

Since you start with saturated air when you shut down, it will stay saturated when it cools to room temperature, but the excess water will have condensed out.  And the engine is pretty well sealed, so I don't expect the water to be removed unless you have an active system to move drier air through the engine.

I am not sure of the exact mechanism, but I suspect that water in the oil doesn't evaporate out as quickly as it would if it was just plain water heated to that temperature.   

Also, there may be an emulsion issue when the engine is running and the oil (and water) are being mixed and whipped.

I see to recall a report of a engine that was just ground run for a number of years that ended up with substantial water in the sump.

Bottom line is, based on what I have read, I will NOT ground run my engine to heat it up and try to remove moisture.  Anyone who wants to do so, please report back how it works.

[MikeOH]

Your first paragraph is exactly why I have an issue with the point of running the engine to 'get rid of moisture'.  It seems to me that upon shutdown all that moisture is going to condense out on everything, just as you say.  So, what's the point? Regardless of ground run vs. flight!
And, again I ask, how does the engine oil 'know' it's being run on the ground vs. in flight?  I.e., why is in-flight effective at getting rid of moisture and ground-run is not?

I tend to agree that 'suspended water', by whatever definition, is likely more difficult to remove than plain water.

I am curious enough to see what it would take ($$) to have sample oil tested for moisture content; I'd love to compare fresh oil (presumably near zero) with 40-50 hour oil. For those that do Blackstone analysis is moisture content reported?  Of course, then we are back to if moisture 'suspended in oil' actually causes corrosion while coated on engine parts.

[Schllc]

22 hours ago, A64Pilot said:

Actual pickling is a lot more than merely putting preservative oil in it, and maybe others can tell the difference but to me it just looks like oil.

Thanks for that explanation, it makes a lot more sense than just putting oil. 
the plane was idle for 20+ years. I would think a proper pickling would have been more than oil and if it was intentional it would have been logged. 
If you intend to leave idle for a period of time, you would want to preserve properly.  Regardless if you wanted to sell or keep, you would want to do it properly.  
Being told it was done, when it was clearly not done is troublesome. 

[Pinecone]

18 hours ago, MikeOH said:

I am curious enough to see what it would take ($$) to have sample oil tested for moisture content; I'd love to compare fresh oil (presumably near zero) with 40-50 hour oil. For those that do Blackstone analysis is moisture content reported?  Of course, then we are back to if moisture 'suspended in oil' actually causes corrosion while coated on engine parts.

Yes, Blackstone reports water.

But if the water condenses and the engine sits for a while, the water will not be in the oil.

[EricJ]

19 hours ago, Pinecone said:

Since you start with saturated air when you shut down, it will stay saturated when it cools to room temperature, but the excess water will have condensed out.  And the engine is pretty well sealed, so I don't expect the water to be removed unless you have an active system to move drier air through the engine.

The engine is vented to atmosphere via the vent and naturally pressurizes a bit.   That's how the oil mist from the crank windage winds up on the belly, and how you can lose a quart via fine mist going out the vent in not very much time if it is overfilled.   It's also why many vent tubes have an ice hole, so that if ice plugs the end of the vent tube the crank pressure doesn't blow the main seal out.    So the motor is actively moving gas through the crankcase, some more than others depending on the amount of blow-by.

That's the mechanism by which it exchanges the existing moisture content, which may be elevated by accumulated condensation, for a lower level.    After shutdown as the engine and case cool it'll draw ambient air in through the vent which can reduce the moisture concentration further.    Again, the idea is that if there is a lot of moisture in the engine from accumulated condensation, that moisture level can be significantly reduced by running the engine up to temperature so that it vaporizes and can be driven out the vent.    The active dehumidifier systems are intended to do the same, but don't refresh the oil films to protect parts, and don't address the moisture in the oil.   They certainly can help to keep moisture off of internal surfaces, though.

If one can't or doesn't want to run the engine, removing a set of plugs and motoring it with the starter will at least refresh the oil film on the important parts.   That doesn't reach the same pressure as when running, and doesn't spray the oil mist from the crank windage around like running it does, but it at least gets the bearings and other surfaces refreshed.

 

19 hours ago, Pinecone said:

Bottom line is, based on what I have read, I will NOT ground run my engine to heat it up and try to remove moisture. 

It certainly isn't required.    People have been leaving engines sit for long periods since engines were invented.   It is sometimes fatal to the engine, sometimes not.

19 hours ago, Pinecone said:

Anyone who wants to do so, please report back how it works.

People have been running engines periodically for preservation since engines were invented.    It is a continuing practice due to the historic success compared to neglecting an engine.  YMMV, everybody does what they think best within their capabilities and circumstance.

[Fly Boomer]

2 minutes ago, EricJ said:

Again, the idea is that if there is a lot of moisture in the engine from accumulated condensation, that moisture level can be significantly reduced by running the engine up to temperature so that it vaporizes and can be driven out the vent. 

It's my understanding that some of the Bonanza people use pre-heat all the time to drive out moisture.

[Pinecone]

44 minutes ago, EricJ said:

The engine is vented to atmosphere via the vent and naturally pressurizes a bit.   That's how the oil mist from the crank windage winds up on the belly, and how you can lose a quart via fine mist going out the vent in not very much time if it is overfilled.   It's also why many vent tubes have an ice hole, so that if ice plugs the end of the vent tube the crank pressure doesn't blow the main seal out.    So the motor is actively moving gas through the crankcase, some more than others depending on the amount of blow-by.

That's the mechanism by which it exchanges the existing moisture content, which may be elevated by accumulated condensation, for a lower level.    After shutdown as the engine and case cool it'll draw ambient air in through the vent which can reduce the moisture concentration further.    Again, the idea is that if there is a lot of moisture in the engine from accumulated condensation, that moisture level can be significantly reduced by running the engine up to temperature so that it vaporizes and can be driven out the vent.    The active dehumidifier systems are intended to do the same, but don't refresh the oil films to protect parts, and don't address the moisture in the oil.   They certainly can help to keep moisture off of internal surfaces, though.

I was not talking about while running, but once you shut down.   I have started removing the oil filler cap after flying.  Amazing the plume of steam coming out.

Another point is, that our oil temps run in the 160 - 180 range.  So it is not like we are boiling off the water.

[EricJ]

19 minutes ago, Pinecone said:

Another point is, that our oil temps run in the 160 - 180 range.  So it is not like we are boiling off the water.

Not at the bearing surfaces or other areas when it is running, it is much higher than that.   That's the temperature when it is entering the engine, it's much hotter when it returns to the sump.

[ArrowBerry]

We also run a Cessna Ag Truck in our business with the IO-550. The airplane sits from October to May generally and we use the Phillips 20W50 Anti Rust oil in it during that time. We change the oil and filter at the end of the season and fly for about one hour to warm the oil to operating temperature and burn off moisture, then park it.

I have read that when using this oil it's important not to turn the prop after you park it because the oil has coated the interior of the engine and you don't want to disturb it. If you are unable to fly, maybe a solution is to change the oil and do a really good run up before parking?

https://www.aircraftspruce.ca/catalog/eppages/phillips20w50.php?clickkey=3032011

[Paul Thomas]

Anecdotally, there was a guy in IL with a Pawnee and a twin. If I recall correctly, he'd (ab)use the Pawnee during spraying season and park it. Maintenance would be done at the beginning of the season. He said he had less engine issues with it than the twin he took great care of.

Without a large scale study, it's hard to know why some things are working and others are not. If my airplane was going to sit for months, I'd hope that I would have been able to take some steps to mitigate potential damage. The reality is that for most of us, those kind of downtimes are unexpected.

I try to run the engine for a minimum of 45 minutes at operating temperature weekly based on the research I've done. Generac programs my air cooled generator to only run 10 minutes each week; I'd imagine they've studied this a lot more than most of us.

[jetdriven]

On 10/26/2024 at 4:25 AM, ArtVandelay said:

When my plane was down for avionics work I just did an oil change. I use Camguard as always.
I have my old camshaft sitting on the floor of the hangar, it’s not showing rust after 5 years and Im in Florida. Based on this I think dirty oil is what destroys engines.

These are lifters out of a 2017 Acclaim Continental engine with 800 hours since new, two days after we were removed from an engine that flew in the day before.  And it flew regularly, was treated right and even had  cam guard in it. 

[A64Pilot]

For whatever it’s worth.

If you seal an engine from air intrusion, a very, very small amount of corrosion will occur, then the O2 is used up and without Oxygen corrosion can’t occur, even if it were filled with water

Way back in the 70’s during the oil embargo there was a push to reduce energy consumption by any means possible including houses as of course electricity and heating oil went thru the roof too.

One way was by thermal mass, mass in a hot day absorbs heat helping keep the house cool and releases the heat at night helping warm the house, particularly in Desert areas where temp swings are large.

One thing that was done to get this mass cheaply was to fill old steel 55 gl drums with water. No matter how long they stayed filled they would never rust out as long as the bung plugs were installed.

 

So in my opinion if you were really very concerned and didn’t want to seal your engine then instead of an aquarium pump pumping air through dessicant and then into the engine you should get a large bottle of N2 and very slowly as in take at least a month to bleed it empty into the engine. The N2 is completely as in absolutely no moisture dry where dessicant will still have some moisture, but also it will purge all of the O2 so.

In truth once you get below about 30% RH there is almost no corrosion. Don’t quote me on that number because it’s from memory but it’s why Desert storage works.

Edited November 8 by A64Pilot

[MikeOH]

@A64Pilot

I think you are spot on.  It's the moisture in the air.

A further data point: I've noticed many city road side electrical 'boxes' have a tank of N2 sitting next to them and feeding in a steady flow to displace the moisture leaden air.

[A64Pilot]

On 10/28/2024 at 3:55 PM, Pinecone said:

Since you start with saturated air when you shut down, it will stay saturated when it cools to room temperature, but the excess water will have condensed out.  And the engine is pretty well sealed, so I don't expect the water to be removed unless you have an active system to move drier air through the engine.

I am not sure of the exact mechanism, but I suspect that water in the oil doesn't evaporate out as quickly as it would if it was just plain water heated to that temperature.   

Also, there may be an emulsion issue when the engine is running and the oil (and water) are being mixed and whipped.

It is unquestionably an emulsion, if it weren’t then you would see free water in the oil when you drained it.

How many auto engines have you seen with blown head gaskets that the oil looks like a milkshake? That is of course because it’s an emulsion. No question that free water in a running engines oil isn’t happening.

Being emulsified is why it takes as long as it does to cook off, I’m sure we have all deep fried something and seen how fast the free water flashes off when the frozen french fries are put into the oil etc.

Somewhere I read that for infrequently flown airplane that it was acceptable to put some amount of preservative oil in the oil and leave it there.

I don’t remember if it was the engine manufacturer or the oil manufacturer. 

Without trying to start a “ bun fight” I think that’s pretty much Camguard is.

[A64Pilot]

33 minutes ago, MikeOH said:

@A64Pilot

A further data point: I've noticed many city road side electrical 'boxes' have a tank of N2 sitting next to them and feeding in a steady flow to displace the moisture leaden air.

I think that’s to purge the electrical wires themselves that run through the ground, I know the telephone company used to do it. I think it flows through the outer sheath of a bundles of wires as I assume they’re not in conduit, but maybe they are?

[A64Pilot]

I think N2 is also used to purge O2 from food packaging, maybe that’s why Twinkies last so long?  

[A64Pilot]

Duck duck go found it, it’s here https://www.phillips66lubricants.com/news/suggestions-for-aircraft-engine-storage-and-infrequently-flown-aircraft/

From the article

“For infrequently flown planes, as one that sits for several weeks to a month or more, we recommend either reducing the drain interval suggested by the engine manufacturer or maintaining the suggested interval and adding a 10% concentration of Phillips 66 Aviation Anti-Rust Oil 20W-50 to the engine oil to boost the rust protection provided by conventional aviation oil. “

Edited November 8 by A64Pilot

[802flyer]

It’s a generalization, but I believe the relatively humidity at altitude tends to be a fair amount lower than at the surface (on a nice VFR day, at least). Skew-T plots show this temp/dewpoint spread well.

I suspect that the conventional wisdom to “run the engine for an hour in cruise to drive off moisture” might take advantage of getting both the air and oil into a low humidity environment. In theory, this will cycle a good volume of dry air through the engine while the oil is hot, aiding in the related-rates process of pulling moisture out of the oil. If any of this makes a difference, I can see why getting to altitude might be better than a ground run.

If moving to Tucson isn’t an option to achieve low humidity, just pick a clear day and climb

Sent from my iPhone using Tapatalk

[Fly Boomer]

1 hour ago, A64Pilot said:

Duck duck go found it

Great article.  Thank you!

[EricJ]

2 hours ago, 802flyer said:

It’s a generalization, but I believe the relatively humidity at altitude tends to be a fair amount lower than at the surface (on a nice VFR day, at least). Skew-T plots show this temp/dewpoint spread well.

I suspect that the conventional wisdom to “run the engine for an hour in cruise to drive off moisture” might take advantage of getting both the air and oil into a low humidity environment. In theory, this will cycle a good volume of dry air through the engine while the oil is hot, aiding in the related-rates process of pulling moisture out of the oil. If any of this makes a difference, I can see why getting to altitude might be better than a ground run.

If moving to Tucson isn’t an option to achieve low humidity, just pick a clear day and climb

Sent from my iPhone using Tapatalk

I think that's exactly right, and why flying it is preferred to just ground runs.   Flying it also allows that exchange of dry air with all of the ventilated spaces on the airplane, including the wings and tail, to help reduce corrosion due to moisture.  If one is limited to ground runs for a non-flying airplane that has been subject to potential condensation inside the engine case, then running it to exchange that moisture with ambient air can still be beneficial if the engine is brought up to temp for sufficient time.   If that's done on a dry day, that's better than if it's done on a humid day.  

[MikeOH]

5 hours ago, A64Pilot said:

I think that’s to purge the electrical wires themselves that run through the ground, I know the telephone company used to do it. I think it flows through the outer sheath of a bundles of wires as I assume they’re not in conduit, but maybe they are?

Maybe.  But cables in the ground are contiguous and covered with insulation. The equipment in the boxes have many CONNECTIONS that would be susceptible to corrosion, I would think.  But I admit to speculation