Bill Boyd

Bill Boyd

Well Known Member
All other considerations aside, there stands a manufacturer's recommendation to change Lyc engine oil every 4 calendar months.

I understand dirt &filtration, moisture & operating temp, 100LL & lead buildup, and acidity in the crank case. Oil and filter changes on the basis of hours in operation, with consideration of extremes in operating conditions such as unavailability of unleaded mogas ;) or frequent, short flights that don't bring the oil temp well into the green make perfect sense to me. We don't want to ask the oil to suspend but so much abrasive dirt and wear metals. But I don't understand nor can I easily imagine the chemistry or physics behind a recommendation that oil be changed every however many calendar months it has been in the engine. I have a feeling the answer may be in the mystical word "additives." I will need some convincing. My mindset is frugal, but not closed.

As a pilot who averages only 40-50 flight hours per year, this is relevant to my situation. I want to know what is allegedly happening to my engine oil in the months that I only fly 3 or four 0.3 hour hops around the patch that would argue for changing it with, say, 12 hours or less total time on it. I've never seen an expiration date on a bottle of 15W-50.

What do we know about this subject beyond conjecture and legend / O.W.T.'s?
 
I'm very interested in this thread as well. It has never made chemical sense to me as it is oil being used is what causes it to 'break down' which is molecules not being so inclined to stay attached to each other: long chain molecules breaking apart to make smaller chain molecules that don't lubricate as well. I think the 'break down' of oil is more why I change oil every 25 hours, even with a full-flow filter, than 50 hours. Is that thinking wrong? A filter will not change that.

And how can oil, sitting in a simi-dormant engine for 4 months need to be changed? There is no breakdown occurring, unless, again, it is the additives. But, as Bill said, there is no expiration date or Best By date on ANY oil I have ever seen. The oil itself is several billion years old. Kind of reminds me of salt having a Best By date. What? What DO we know about this beyond rumor and innuendo. Oil companies making more money? Cynical.....:cool: Hmmmmmmmmmmmmmm.......:unsure:
 
I was “schooled” by past mentors over my 30 years of wrenching that oil should be changed at 50(25) hours or annually, whichever comes first (barring any abnormal operating conditions) The 4 mo interval caught me by surprise.
I too am very interested in this.

Thanks for posting!
 
Bill Boyd said:
All other considerations aside, there stands a manufacturer's recommendation to change Lyc engine oil every 4 calendar months.

I understand dirt &filtration, moisture & operating temp, 100LL & lead buildup, and acidity in the crank case. Oil and filter changes on the basis of hours in operation, with consideration of extremes in operating conditions such as unavailability of unleaded mogas ;) or frequent, short flights that don't bring the oil temp well into the green make perfect sense to me. We don't want to ask the oil to suspend but so much abrasive dirt and wear metals. But I don't understand nor can I easily imagine the chemistry or physics behind a recommendation that oil be changed every however many calendar months it has been in the engine. I have a feeling the answer may be in the mystical word "additives." I will need some convincing. My mindset is frugal, but not closed.

As a pilot who averages only 40-50 flight hours per year, this is relevant to my situation. I want to know what is allegedly happening to my engine oil in the months that I only fly 3 or four 0.3 hour hops around the patch that would argue for changing it with, say, 12 hours or less total time on it. I've never seen an expiration date on a bottle of 15W-50.

What do we know about this subject beyond conjecture and legend / O.W.T.'s?
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Bill,
I seem to remember seeing something about this on the Blackstone website but can’t seem to find it right now. I will dig a bit to see if I can locate it.

I was able to locate a document on the Blackstone website, https://www.blackstone-labs.com/wp-...13-07-01-How-Often-Should-I-Change-My-Oil.pdf

Mark
 
The article also mentions that it doesn't matter which brand of oil you are using, as long as you use quality aviation oil.
 
I can answer this, at least one of probably a few reasons....

the way it was explained to me is this.
Oil is a mixture of polymers of different lengths. The shorter chained polymers tend to evaporate. If you leave a sump long enough, the short chains go away, leaving only the long chains along with whatever dirt is left behind = SLUDGE

and I reckon that's why my mom's car's engine back when I was a kid had so much sludge in it.... it burned a little oil so we would add a quart as needed....and sadly would rarely change it...basically never.....

my source:
Way back when I was straight out of college (ME) working as a maintenance engineer at a large pulp and paper mill..this would have been in the early 1990's..
One of the many responsibilities of my job was to maintain the lubrication database. We bought all our lube oil from Texaco. Texaco's lubrication engineer would come in periodically and my group would assist them in taking their samples, and then we would receive and distribute their reports, etc...

So this is coming from one of the Texaco engineers after I asked this very same question.....
 
Roadjunkie cites a common understanding that engine oil gets "blenderized" by mechanical shearing action and ends up as shorter polymers with less lubricity. I've read pro and con on this theory - some say it happens and makes a discernible difference, while others doubt it matters. Either way, that isn't a function of time sitting in the engine, but of time in a running engine.

Blw2 raises an interesting possibility - differential rates of evaporation of hydrocarbon chains based on length, ultimately affecting the mechanical properties of the oil. This could certainly happen in an engine while it sits, vented to atmosphere.

I wonder if there is the possibility of very slow, largely temperature-independent reaction of oil or additives with the chemical products of combustion that accumulate in the crank case. We end-users would have no way of quantifying this - it would be the purview of a petrochemical lab with knowledgeable engineers to tell us if this is the case. Reading the Blackstone article that Mark posted, it would seem that they don't believe it, at least as far as acidic compounds are concerned.

Blackstone implies that it's not the oil itself that changes over calendar time, but the engine itself - it rusts, and sheds corrosion products, some very abrasive, into the oil. I had always heard that the oil film on the overhead cam and upper reaches of the engine could protect against corrosion for roughly a month - give or take depending on synthetic vs mineral stock. This may vary significantly by geographic location and average humidity and salt levels.

I'd love to send for analysis a blind sample of oil run to 50 hours in just a few weeks immediately before collection, and a sample run in the same way followed by sitting in the engine for 6 months. Not that would be good for the engine ( ! ) but it might tell us for certain if the oil and additive package is harmed / modified by sitting on its dregs and stewing for a few months.

I'd also like to see some red-tagged cams cleaned, polished, oiled with good aviation oil and placed in a Divco-reject crank cases and observed for surface corrosion - with and without a dehumidifier in use. That would be instructive. Same for a cylinder and piston. Actual days-to-film-breakdown numbers would be nice to know.
 
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Bill Boyd said:
Blw2 raises an interesting possibility - differential rates of evaporation of hydrocarbon chains based on length, ultimately affecting the mechanical properties of the oil. This could certainly happen in an engine while it sits, vented to atmosphere.
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At room or most ambient temperatures, oil will not evaporate; at least not at a rate you could measure. Oil evaporation occurs at high temperatures, related to its 'boiling point'. One controlled test showed that 50ml of refined oil heated to 100C (212F) for 24 hours will lose 0.16% of its weight. A liter of oil weighs approximately 860 grams. A 0.16% loss of its weight at that temperature for 24 hours would be about. 1.376 grams. At ambient temperature, you would not likely be able (or interested in) measuring the evaporative loss. 😊
 
When I asked Lycoming tech about this, I was told that the 4 months is not an absolute and it has some to do with how frequently it is flown. The reason for it had to do with the harmful chemicals that is release from burning fuel which if it sits for extended time, it becomes more harmful. So in short, the more often you fly the more you can go pass the 4 months period.
 
Bavafa said:
When I asked Lycoming tech about this, I was told that the 4 months is not an absolute and it has some to do with how frequently it is flown. The reason for it had to do with the harmful chemicals that is release from burning fuel which if it sits for extended time, it becomes more harmful. So in short, the more often you fly the more you can go pass the 4 months period.
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And what happens if you fly it more often? You replace any "harmful chemicals from the burning fuel" that you might boil off in flight with a brand new batch of the same harmful chemicals. This is exactly what I don't get about the recommendation. It's as if we're conflating flying several times a month with changing out the oil several times a month.

The only thing that makes any sense to me so far is Blackstone's speculation that our engines begin to corrode internally very soon after their most recent use, and it's those corrosion products that need to be got rid of through an oil change whether the engine racks up meaningful Hobbs time in that interval or not.
 
Roadjunkie1 said:
There is no breakdown occurring, unless, again, it is the additives. But, as Bill said, there is no expiration date or Best By date on ANY oil I have ever seen. The oil itself is several billion years old. Kind of reminds me of salt having a Best By date. What? What DO we know about this beyond rumor and innuendo. Oil companies making more money? Cynical.....:cool: Hmmmmmmmmmmmmmm.......:unsure:
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I had a case of AeroShell that had a use by date stamped on the case. Asking the "AeroShell man" at AirVenture Oshkosh about the date, they told me to NOT use the oil beyond that date. Being a "cheap" pilot, I did not use the oil for oil changes but did use the oil one quart at a time as make up oil added between changes.

I am not an oil expert and just want to learn.
 
RV6_flyer said:
I had a case of AeroShell that had a use by date stamped on the case. Asking the "AeroShell man" at AirVenture Oshkosh about the date, they told me to NOT use the oil beyond that date.
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Oh, I would have jumped all over THAT! My next question would have been 'Why? What happens to the oil sitting in a closed container?' and either watch him grab at straws or come up with some gobbledegook about oil breakdown in the bottle. I might have added 'If your oil is THAT unstable, I might want to consider Phillips instead.' I'm no oil expert either but I believe that answer was AeroShell for "Buy more of our oil". But what do I know.....my bag of pink salt has expired. Guess I'd better toss it...... 😝
 
I suspect the 4 month calendar limit is there for precisely the same reason Lycoming has a 500 max CHT limit. Because both of them will be happy to sell you replacements.
 
Time to get Horton on the case!

Somebody should start a poll so all of those folks who haven’t adhered to Lycomings 4 month recommendation can chime in without being outed.

I’ll go out on a limb and suggest very few follow Lycomings 4 month interval.
Anybody been through AP school lately? Wonder what they are teaching or even if it is covered as such.
 
JonJay said:
Time to get Horton on the case!

Somebody should start a poll so all of those folks who haven’t adhered to Lycomings 4 month recommendation can chime in without being outed.

I’ll go out on a limb and suggest very few follow Lycomings 4 month interval.
Anybody been through AP school lately? Wonder what they are teaching or even if it is covered as such.
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I change mine at 50 hour intervals. No adverse oil analysis from blackstone.
 
georgemohr said:
I don't know of many people that change oil on elapsed time. It feels somewhat like the overhaul interval on elapsed years instead of tach hours...
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My current cars only track oil change by miles driven, so this makes sense. Though by the book it asks for once a year.

Personally I do change it on my plane at approx 6 months if I haven't clicked enough tach hours but 4 months seems excessive, especially during periods of limited flying. I try time one of those changes for when icing season is kicking in.
 
gasman said:
If you burn a quart in 10 hours, you should never have to change your oil.....:)
Just spin on another $5 WIX and go.
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Not exactly! Draining oil removes contaminates that will settle out of the oil and produce sludge. That's why you should drain the oil immediately after a run while these contaminates are still suspended in the oil.

I'm sure that your post was in jest, but some folks believe everything they read on the internet. (In spite of Abraham Lincoln's famous quote.)
 
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JonJay said:
…..Anybody been through AP school lately? Wonder what they are teaching or even if it is covered as such.
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I’ll bet any amount of money they teach “follow the OEM guidelines/reccomendations”. The schools aren’t going to expose themselves to anything. An A&P license, like a diploma, is a license to learn. Takes experience and seasoning to start questioning the black and white.

Sad thing = the guys with the vast amount of experience/knowledge are disappearing from the field for various reasons. One reason I left certified world. Everybody would rather replace components versus apply some troubleshooting/common sense/expose themselves. Ding something? it’s gonna get replaced on whole at $8K versus a $1K repair. Maybe others have been more fortunate.

Bio break over. Back to work.
 
I was always told that oil oxidizes over time and can lose the quailities we employ it for. This is regardless of the running hours. I must admit I've never researched this or challenged it and I'm sure we have some experts on here who can comment, however it seems feasible to me. Certainly in the industry I work in we have equipment which has a recommended oil replacement based on calendar rather than hours so at some level some guru has found this to be beneficial for reasons above my pay grade. Allowing oil sit in the engine with a high moisture content or high levels of acidic contaminants for an extended period of time doesn't seem prudent, just to save a few dollars on an oil change.

Without having gone into the science I feel its prudent to replace the oil in my engines at an hourly interval or a calendar interval, whichever occurs first. Personally I do 50 hour/12 monthly cycles as its convenient to my maintenance cycle. No point pulling the cowls off a week after doing an Annual just to change the oil and filter when you could have done it while you had access.
 
I'm still using Pennzoil 2-stroke oil in my weed eater that was left over from my RANS S-12 Rotax 582 days. That plane was sold in 1994. 30 years later when I look into a bottle, it has not reverted to dinosaurs (if it ever was - I see there is some controversy about how and why the term 'fossil fuel' was ever introduced into the vernacular, but that's a topic for another day and some other site).

If my 2015 -era Stihl Kombi weed eater doesn't make TBO, I'll fess up here so we'll know. ;)
 
Been googling all afternoon and the polymer shearing is always referred to as a result of mechanical action, such as in a running engine. Nothing on why oil simply sitting in an engine would deteriorate appreciably. Most actually suggest that it's the additives that break down sooner, but not faster than a year or so, which seems to be the common advice on how often to change automotive engine oil with limited use.

Chris
 
I was in Argentina on a mission trip back n 1996 and went into a shop and bought three 10" tall SOLID BRASS camels. There was a label on the bottom that said DO NOT EAT.
Go figure!!! There are al sorts of warning we do not follow.
I for one, being a mechanic for 55 years have serious doubts the engine is going to blow up or even have problems if you don't follow the manufactures advice.
Yes, I change my oil every 25 or so hours and filter every other. But, I am just now in the process of installing a rebuilt engine in my RV-6A.. Just yesterday I poured in 7 quarts of mineral oil that has been under the bench for at least 25 year. Looked like oil to me.
Oh ya the engine was overhauled in 1993 and kept in a warm place with no oil in it or spark plugs since then.. I am going to see it it works or not in a couple days.
Maybe maybe not. I borescoped the cam and cylinders and seen nothing amiss.
Maybe it will blow up cause the oil is 25 year old ???
I did put the oil in it upside down and rolled it around to get oil everywhere in the engine. And put the fly wheel and starter on to crank the engine with no plugs to get the oil through everywhere else.

BUT my luck varies FIXIT
 
gasman said:
If you burn a quart in 10 hours, you should never have to change your oil.....:)
Just spin on another $5 WIX and go.
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Off topic, but I found this ineresting.

I was on a cruise ship recently and attended a Q&A with the ships officers. I asked the Chief Engineer "how often they change oil in the engines". These ships have five very large diesel engines. HIs answer "NEVER". He explained, they have very systificated filter systems including centrifigal particle separators, and do oil analysis regularly. Seems suspect, but I confirmed this with an engineer on another ship (different cruise company) and he agreed. Rate of make up oil? I don't know. Of course these engines are run frequently.

OK, back to the subject at hand.
 
The way it was explained to me was that oil is hygroscopic, will absorb moisture from the humidity in the air in the sump and carry it as an emulsified suspension of moist globules through the engine's internal oil passages.

Combustion products of water in oil include acids, which make the oil corrosive. Running the engine to boil the moisture off doesn't completely cure that because the acids form before it's reached operating temperature.

So there's a service hours limit related to oil degradation caused by contaminant load and long chain polymers mechanically shearing, and a separate calendar limit related to moisture. Presumably different depending on relative humidity in its storage location.

I'm not emotionally attached to any of this explanation, which was passed on to me third-hand and could be an old wives' tail as much as anything else on this forum. It makes a certain amount of sense, but could just as easily be hogwash. I'd love to know if there's a pH difference between fresh oil and 4 month old sump oil, though.

(don't contaminate your oil with hog wash, the hairs will clog your oil filter)

- mark
 
It would be interesting to do a simple pH comparison as Newt suggests. I wonder what instrument would be needed. Highly doubt standard pH paper from the biochem lab would work on a non-aqueous solution. I have some of that litmus paper at the house but not an electronic probe-type of meter. The issue would seem to be one of adequately wetting the reagents on paper or wetting the active area of the probe with the fine droplets of water/acids suspended in the oil... if I understand pH correctly (Chem 101 was a long time ago), it only applies to aqueous solutions and not liquid hydrocarbons, which don't dissociate into H+ and OH-. Measuring those little buggers is probably not the easiest thing to do. Hopefully an engine manufacturer has tracked the rate of acid formation in fresh oil as the hours of run time accumulate - if the rise in acidity is rapid, I would see little benefit in frequent calendar change intervals, as the protection from a change/flush would be largely undone by putting the first few hours on the new oil. If the buildup to potentially corrosive levels is slow, then a calendar-based change interval would do more to reset the clock on acid exposure.

Any petrochemical engineers on here?

Afterthought: a centrifuge would aid in separating the suspended water from the oil and getting a sample for pH analysis. I returned my centrifuge to LabCorp when I closed the office last year, so I can't be of much help 🤷‍♀️
 
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Bill Boyd said:
It would be interesting to do a simple pH comparison as Newt suggests. I wonder what instrument would be needed.
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The company I work for have a RULER test unit approved for testing the condition of turbine oils - not sure it works on piston-engine oils, but the idea is you test the oil from time to time to determine whether or not you need to replace it. Saves dropping the oil out unnecessarily. The principle is good but none of my customers use it. Not sure why... probably due to the cost of the approved equipment.
 
tass said:
My current cars only track oil change by miles driven, so this makes sense. Though by the book it asks for once a year.

Personally I do change it on my plane at approx 6 months if I haven't clicked enough tach hours but 4 months seems excessive, especially during periods of limited flying. I try time one of those changes for when icing season is kicking in.
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my 2006 Silverado tracked and suggested oil change intervals by more than just miles. the computer looked at other variables too...don't remember exactly, but I recall it being time, temperature, how hard it was driven, etc...
Hard to believe that newer cars don't do at least that.
 
Blw2 said:
my 2006 Silverado tracked and suggested oil change intervals by more than just miles. the computer looked at other variables too...don't remember exactly, but I recall it being time, temperature, how hard it was driven, etc...
Hard to believe that newer cars don't do at least that.
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They do, or at least the newer F150’s do.
I think it’s pretty common now.
 
Blw2 said:
my 2006 Silverado tracked and suggested oil change intervals by more than just miles. the computer looked at other variables too...don't remember exactly, but I recall it being time, temperature, how hard it was driven, etc...
Hard to believe that newer cars don't do at least that.
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Something else for the experimental avionics manufacturers to write code for. (Hopefully not until after they take my suggestion to incorporate verbal commands for input instead of buttons, knobs, joysticks and touch screens that all suck in turbulence).
 
Ah, but you can do that, HAL. We've had smart phones and laptops that could do it for well over a decade.

Your designers just don't see a market, don't want to get a license to use the subroutines, or think we're more interested in synthetic vision, which is stunningly beautiful at first, but ultimately likewise almost useless. But that's another thread for a different day. Benefit of the doubt: they're laboring to bring something like G@rm1n's auto-land to the masses that bought some other brand.
 
erich weaver said:
Good one.
“Alexa, change com frequency to 122.8”
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Drifting a bit here, but funny...

A couple years ago I was flying my dingbat sister-in-law home to San Marcos, she has no aviation background and was chatting away about all the important things in her inane world. I had a couple waypoints on the flight plan and about 5 seconds before I hit one of them I picked up my phone and said "Hey Siri, give me 20 degrees right" and the autopilot faithfully followed the magenta line. She nearly lost her mind - "How did you do that? I can't even get Siri to answer me, and you've got her driving the plane!"
 
erich weaver said:
Good one.
“Alexa, change com frequency to 122.8”
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I can see things getting spicy in my cockpit.

Pilot: "Alexa, go check on George - he's like a drunk sailor trying to hold altitude today."

Autopilot: "Not my fault! Every time I ask for a bit of trim, the servo fights me more than before. It's all so tiring..."

Pitch servo: "Clutch slip detected. Just try'n'a do m y job, man..."

Pilot: "Alexa, check George's settings for trim tab direction sensing - they were backwards once and we fixed that."

EFIS: "Well it seems they're backwards again, Skipper. I would make correction but as you know we cannot access those settings in flight. Suggest you hand-fly, or settle in for an E-ticket roller coaster ride."

Autopilot: "I'm not the only victim of my programming, here. Remember that time you refused to set the approach frequency because Skipper said 'One two four dot three nine' instead of 'One two fo-wer dot tree niner'? Pepperidge Farm remembers! Not your best day..."

Pilot, using buttonolgy: SET / CHECK / VOX COM / MUTE ALL

EFIS, over-riding the MUTE setting: "I see you're due for an oil change, Skipper. 13 hours tach time but it's been 121 days - VAF never settled that question so I must default to the Lycoming factory recommendation. Avalilable power will be reduced to 65% until you comply."

Pilot, screaming: "You can't do this to me! What are you, the Diesel Exhaust Fluid Lady?! I may need full power for an emergency!"

EFIS: "Also, according to VAF, you used the wrong primer and there should not be a parking brake in here. Why is your harness unbuckled? Why is the pilot side door unlatched? I'm detecting a sudden change in CG..."
 
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RV6_flyer said:
I had a case of AeroShell that had a use by date stamped on the case. Asking the "AeroShell man" at AirVenture Oshkosh about the date, they told me to NOT use the oil beyond that date. Being a "cheap" pilot, I did not use the oil for oil changes but did use the oil one quart at a time as make up oil added between changes.

I am not an oil expert and just want to learn.
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We need to be carefull of these warnings though. Between legal and marketing dept's, these have become popular tools to shed liability and drive incremental revenue. I remember 10 years ago my wife throwing out a bottle of eye wash solution for her contacts. I asked why are you doing that and she said it has expired (5 year expiration date on label). I grabbed the bottle and ingredients said saline solution. Since when does saltwater have an expiration date? Someone needs to tell the guys taking care of the oceans that they need to change the water :cool: certainly some things have an expiration, but the popular new tactics make it harder to determine fact from marketing.
 
lr172 said:
Since when does saltwater have an expiration date?
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The explanation I usually hear about that is an expiration for the bottle itself. So they guarantee it's sterile/fresh for up to 5 years, because beyond that the bottle may begin to let outside contaminants in or the bottle itself may begin to leech into the product. There's usually a second way to tell you how long you should keep an already-opened bottle.
 
tass said:
The explanation I usually hear about that is an expiration for the bottle itself. So they guarantee it's sterile/fresh for up to 5 years, because beyond that the bottle may begin to let outside contaminants in or the bottle itself may begin to leech into the product. There's usually a second way to tell you how long you should keep an already-opened bottle.
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From all I have read, one of the larger problems facing our oceans and their inhabitants is that plastic DOES NOT break down over time. I won't argue against them leeching chemicals into their contents, but highly suspect that the rate of leeching is constant from day 1 to day 1,000,000. While I have not looked, I suspect that I would find the same expiration date even if a glass bottle was used. Possibly I have become jaded by big business and therefore biased.
 
lr172 said:
From all I have read, one of the larger problems facing our oceans and their inhabitants is that plastic DOES NOT break down over time. I won't argue against them leeching chemicals into their contents, but highly suspect that the rate of leeching is constant from day 1 to day 1,000,000. While I have not looked, I suspect that I would find the same expiration date even if a glass bottle was used.
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Fair call, though I've come across old bottles of things where the seal itself (the spongy piece glued in the cap) has hardened or the glue on the peel-off seals was ineffective. It could be much longer than 5 years, but these things need some kind of date to at least prevent them being sold. Motor oil is probably a lot less of a problem than something that ultimately ends up in your eyes, though.
 
While I generally will use oil no matter its age, I can make one observation regarding AeroShell Turbine oil. When I open a fresh can (yes, it still comes in cans, not plastic bottles!), it is almost clear. I use about a third of a quart for an oil change in th little jet engine, so the rest of the can goes in a sealed bottle - but over time, the color changes to a light orange/red…and all its doing is sitting there on teh shelf, not being run in an engine. When I drain used oil out of the engine, it has that same reddish color.

So just saying - some changes (good, bad, or indifferent) happens once you expose it to air. Something changes - I just don’t know what!
 
If it looks like oil, smells like oil, and tastes like oil, it’s oil!
Credit “Cheech and Chong”, young folks can google it!
 
Ironflight said:
While I generally will use oil no matter its age, I can make one observation regarding AeroShell Turbine oil. When I open a fresh can (yes, it still comes in cans, not plastic bottles!), it is almost clear. I use about a third of a quart for an oil change in the little jet engine, so the rest of the can goes in a sealed bottle - but over time, the color changes to a light orange/red…and all its doing is sitting there on the shelf, not being run in an engine. When I drain used oil out of the engine, it has that same reddish color.

So just saying - some changes (good, bad, or indifferent) happens once you expose it to air. Something changes - I just don’t know what!
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Ya but Paul you don't know if the color change is for the better or the worse. Maybe it's getting better like a fine wine.
My luck varies FIXIT
 
airguy said:
Drifting a bit here, but funny...

A couple years ago I was flying my dingbat sister-in-law home to San Marcos, she has no aviation background and was chatting away about all the important things in her inane world. I had a couple waypoints on the flight plan and about 5 seconds before I hit one of them I picked up my phone and said "Hey Siri, give me 20 degrees right" and the autopilot faithfully followed the magenta line. She nearly lost her mind - "How did you do that? I can't even get Siri to answer me, and you've got her driving the plane!"
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Hey, I forgot that word altogether... can I have permission to revive it? Got some folks who really fit the dingbat model in my immediate environment.
 
Ironflight said:
While I generally will use oil no matter its age, I can make one observation regarding AeroShell Turbine oil. When I open a fresh can (yes, it still comes in cans, not plastic bottles!), it is almost clear. I use about a third of a quart for an oil change in th little jet engine, so the rest of the can goes in a sealed bottle - but over time, the color changes to a light orange/red…and all its doing is sitting there on teh shelf, not being run in an engine. When I drain used oil out of the engine, it has that same reddish color.

So just saying - some changes (good, bad, or indifferent) happens once you expose it to air. Something changes - I just don’t know what!
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Yeah, MANYYY chemicals change over time due to oxidation (i.e. exposure to oxygen). Take a bottle of ketchup. Never open it and it will last for decades. Open it, use some and reseal it without refrigeration and it spoils, which I believe is due to exposure to O2. A better test of your oil would be to let the can sit for 20 years then open it. My wager is on it being clear.

So, I think we need to differentiate between a sealed oil container and oil sitting in a sump. I suspect a significant difference in shelf life. I also tend to fall on the side of Lyc, that the time for the oil to go bad being directly related to how many foreign contaminates it contains.

Larry
 
I had a 15 year career in refining. Hydrocarbon based lubricants will turn amber colored over time and when subjected to UV. It doesn't affect the lubrication properties. We would replace lube oil on our large compressors and turbine trains once every 5 years or more depending on the turnaround cycle. A lube oil change would cost $20,000 in materials alone and was always heavily debated. In my experience, oil in our ICE's living adjacent to combustion gases accumulates all kinds of unwanted material hence the 50 hour limit. Storing oil in a non running engine is no different than circulating oil through the lube oil system of a 7,000hp steam turbine. It lasts many years without degradation.
 
Bill Boyd said:
Ah, but you can do that, HAL. We've had smart phones and laptops that could do it for well over a decade.
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Wow, I think you really missed the point of the clip from "2001: A Space Odyssey" and the HAL 9000!
 
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