Oil darkens quickly

RyanB

RyanB

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The oil in the Archer turns opaque pretty quickly. By 15-20hrs it’s getting dark. By 25 it’s opaque. It seems like it should look pretty clean for several hours beyond this, as does the oil in other aircraft I fly. The engine hardly burns any oil (~13hrs/qt) and the compressions are in the low to mid 70’s. I don’t do oil analysis, but maybe that would provide some sort of explanation? I know they say not to change oil based on color, but I have a hard time choosing not to, when I can barely see through it at 25hrs.

Any reason in particular why it would darken up so quickly?
 
I am not an IA or AP... but I've never heard of changing oil based on color.

And why wouldn't you start the oil analysis?
 
I'm guessing one ring is stuck enough to hasten the oil color change but maybe not enough to burn through it quickly.

We have one ring sticking. It discolors the oil in about 8 hours but burns between 1...1.5qts in that time.

Look at the airflow where the exhaust will hit the airframe, is it abnormally dirty or black. Our copilot cowl flap is another indicator.

Hopefully yours is simpler.
 
That is a good thing, it means that your oil is doing its job, and cleaning the engine as designed.
My oil does the same thing, and around 50 to 55 hours I change it.
 
RyanB said:
Any reason in particular why it would darken up so quickly?
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The are various reasons why oil darkens but for the most part it's a normal process. For example, radials tend to darken oil very quickly vs horizontal engines. So long as there is no increase in debris/particles in the oil then everything should be good. But if curious as to what some of the reasons are that affect the timing of the color change: piston ring/cylinder tolerances, dirty sump area, type/brand of oil, oil additives, type engine, etc.
 
Could just be the carburetor is providing a richer mixture at full power than the other planes you fly and more carbon is deposited in the oil.
 
Building on what @Sinistar said, look at your lower plugs. If one is really oily, that might be the cylinder with the ring issue (if that's the problem).
 
Hang 4 said:
Building on what @Sinistar said, look at your lower plugs. If one is really oily, that might be the cylinder with the ring issue (if that's the problem).
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Mechanic pulled the plugs not long ago and despite some lead deposits, they all looked fine. Might be worthwhile to check again.
 
Do you ever check your oil color after a flight? Or only before?
 
RyanB said:
The oil in the Archer turns opaque pretty quickly. By 15-20hrs it’s getting dark. By 25 it’s opaque. It seems like it should look pretty clean for several hours beyond this, as does the oil in other aircraft I fly. The engine hardly burns any oil (~13hrs/qt) and the compressions are in the low to mid 70’s. I don’t do oil analysis, but maybe that would provide some sort of explanation? I know they say not to change oil based on color, but I have a hard time choosing not to, when I can barely see through it at 25hrs.

Any reason in particular why it would darken up so quickly?
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It's supposed to darken. What are these other planes you talk about where it doesn't? How much time on each of the engines? What kind of oils are used in each? Additives? Does non detergent oil figure into any of this?
 
How are your cht's?

Do you run 65%, 75%?

ETA: I was just commenting to my mechanic how much I hate trying to check fresh oil and wish they'd put some dye in it. Starting to darken up by 25 hours sounds about right. I change at 50 and it's maybe not black, but pretty dark.
 
asicer said:
Do you ever check your oil color after a flight? Or only before?
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Only before. Of course right after a flight it’s nice and translucent from being hot and churned up. Once it cools and settles the color becomes much more opaque.

Just took this image this morning. 25.3hrs.

728EC671-2F1F-4380-8395-35141AA93386.jpeg
 
luvflyin said:
It's supposed to darken. What are these other planes you talk about where it doesn't? How much time on each of the engines? What kind of oils are used in each? Additives? Does non detergent oil figure into any of this?
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I realize that, I’m just questioning the rate at which it darkens, to determine if there’s something I need to be considering or if it’s just par for the course. Two other airplanes I fly seem to retain a translucent and clean colored oil beyond 25hrs. Their engines are newer (calendar time) than the O360 in the Archer. Same oil (Phillips XC) and CamGuard additive.
 
RyanB said:
Only before. Of course right after a flight it’s nice and translucent from being hot and churned up. Once it cools and settles the color becomes much more opaque.

Just took this image this morning. 25.3hrs.

View attachment 107702
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That's fairly dark for 25. How many hours on the engine? The archer I used to fly would get like that as it got closer to tbo.
 
Jim K said:
That's fairly dark for 25. How many hours on the engine? The archer I used to fly would get like that as it got closer to tbo.
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475SMOH in 1997. It didn’t fly much before I got a hold of it, but that said, compressions are good, doesn’t burn oil and the filters have been clean.
 
RyanB said:
Only before. Of course right after a flight it’s nice and translucent from being hot and churned up. Once it cools and settles the color becomes much more opaque.

Just took this image this morning. 25.3hrs.

View attachment 107702
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Translucent from being stirred up?? That may just be a result of what sticks to the stick. Cold, it's a thicker layer. Hot, thinner layer. However much 'stuff' there is in the oil, theres less of it to look through to see the stick underneath. As you can see from that pic, by the time you pull it out, it's already thinning out at the top by the 6 qt mark. looks a little cleaner up there. But it's all the same oil.
 
luvflyin said:
Translucent from being stirred up?? That may just be a result of what sticks to the stick. Cold, it's a thicker layer. Hot, thinner layer. However much 'stuff' there is in the oil, theres less of it to look through to see the stick underneath
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Exactly what I’m referring to.
 
luvflyin said:
Oh. Gotcha. I thought you might have been implying that somehow being hot and stirred up somehow made the actual cleanliness of the oil different
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Nope. :)
 
RyanB said:
Only before. Of course right after a flight it’s nice and translucent from being hot and churned up. Once it cools and settles the color becomes much more opaque.

Just took this image this morning. 25.3hrs.

View attachment 107702
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Looks normal for 25 hours in ever plane I've ever flown. My Aztec oil looked at least that dark in 5 hours, not 25.
 
RyanB said:
Only before. Of course right after a flight it’s nice and translucent from being hot and churned up. Once it cools and settles the color becomes much more opaque.

Just took this image this morning. 25.3hrs.

View attachment 107702
Click to expand...

Always hard to tell in photos but that doesn't seem terribly abnormal for a carbed engine to me. I wouldn't worry unless it's black.
 
I know a boat powered by a pair of Detroit Diesel 6V-53’s that were run at 100% power for hours on end. The oil turned pitch black within a few hours of an oil change. Boat was sold after 6000 hours so I lost track of it.

-Skip
 
Skip Miller said:
I know a boat powered by a pair of Detroit Diesel 6V-53’s that were run at 100% power for hours on end. The oil turned pitch black within a few hours of an oil change. Boat was sold after 6000 hours so I lost track of it.

-Skip
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I change oil in city diesel trucks for 30+ years now. Oil is black soon after I start it back up after a oil and filter change. They run for 1/2 million miles in the city.
The latest Detroit DD13 diesel engine has a 45000 mile oil change interval.
 
Might not be leaning enough in cruise. More carbon past the rings, especially if compressions are falling off.

The heat alone will darken the oil.

Are you draining the used oil hot, right after a good runup? If not, the black stuff settles out of it and lays in the sump instead of draining with the oil. That will darken the new stuff right away.
 
Oil migrates around some of the hottest spots in the engine. Among them are Cylinder Heads, Exhaust Valves and the underside of Pistons. Some of these areas may be hotter than shown on CHT.

High heat alone will darken most oils. When checking for contamination I put some of the oil on a clean tissue and hold up to the light. Golden = good & Black =bad
 
OP what does oil analysis say?
If not doing any, why not do it for at least the 3 next oil changes and look for a trend.

I do oil sampling every 2nd oil change.
 
Mine tends to go from invisible right after change, to a darkish honey at about 30-35hrs...then pretty dark by 50. Never black or opaque on the stick, but a jar full does look 'pretty much' black at 50.

The FBO I trained at had 2 DA40's and two 172's. None of those had black oil on the stick that I ever saw in the three years I rented there.
Another FBO I rented from for about 2 years, always had the blackest oil on the dipsticks I've seen in any planes, and it was seemingly across the board. Warrior, 172, 172 Cutlass, etc.
I know the Warrior was at 2000 hrs when they replaced it (and was still running).

Not sure what the difference is.
Maybe like Dan said, one of them changed oil without warming up first.
I doubt leaning was a difference as they both were flight schools and probably got the same renter mixture. (no pun intended)
 
Well, I got my oil changed, the clock is reset and I’ll keep an eye on things. Thanks for the thoughts everyone!
Dan Thomas said:
More carbon past the rings, especially if compressions are falling off.
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Compressions aren’t falling off, if anything they’re holding steady the past few years and rising a little since I’ve been flying it regularly.
 
In straight propane fueled engines it doesn’t darken. I’ve always been told it’s the carbon from the fuel that darkens it.
 
My last oil change was a week ago, and I didn't take a sample from it, but did from the oil change before that. The oil had 53.7 tach hours on it, looked filthy, yet the oil analysis came back good, and the oil still had plenty of service life left in it. I've been thinking about going to 75 to 80 hour oil changes, as it's never close to the end of its life at 50 to 55 hours.
 
Whitney said:
the oil still had plenty of service life left in it. I've been thinking about going to 75 to 80 hour oil changes, as it's never close to the end of its life at 50 to 55 hours.
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FYI: the oil is changed not due to a lack of "service life" but due to contamination. One of the biggest culprits being the fuel used. And even though oil change intervals are only recommendations, some OEMs actually provide a way to go to 100hr oil changes with a filter or 50hrs with a screen provided you use one of the approved unleaded fuels out there.
 
Rgbeard said:
You'd **** your pants if you saw what the Turbo Lance looked like after only five hours. ;)
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Word. By some on here, they'd probably snitch me to the FAA if they saw my engines oil color and burn rates. During my O-320 days my version of oil change was, add more oil. I don't even ....do oil analysis.
freak-out.gif

:rofl:


Me and the clean your belly/oil analysis crowd just don't run in the same circles. Takes all kinds.
 
Bell206 said:
FYI: the oil is changed not due to a lack of "service life" but due to contamination. One of the biggest culprits being the fuel used. And even though oil change intervals are only recommendations, some OEMs actually provide a way to go to 100hr oil changes with a filter or 50hrs with a screen provided you use one of the approved unleaded fuels out there.
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When i had my Citabria it was flown so much that I changed it every 90 to 100 hours, whether I was supposed to or not. I flew the heck out of that poor thing, damn it was a good plane, despite being small and slow.
And if all you had to land on was a short road, beach, gravel bar, or dozer scraped area at a gold mine, it was up to the task.

First time I flew into a large airport with it, joked with the controller when cleared to land, if I should use the runway sideways, the width was so enormous.
He laughed, and suggested that I still use the length.
 
After about 600 hours on Swift 94 the oil is definitely staying cleaner longer on our O-200 which now has 1500 hours on it from new.

Now changing the the aeroshell 15W50 every 75 hours and will probably increase that to 100 hours at some point. Never got any oil analysis done and it will be interesting to see what the insides are like when its stripped at overhaul.

Zero lead fouling problems and had one spark plug replaced in the last 800 hours.

Unleaded fuel it's the way forward.
 
My 2 cents... I am an A&P and I'm on my third personal airplane and have flown professionally for 45 years twenty of which I flew and maintained a brand-new Cessna 340A for twenty years and over 8000 hours.
The oil turning dark is a result of blow-by from the combustion process. All air-cooled aircraft engines do it to some degree. Compression readings tell you nothing about the cylinder health below TDC. I do compression checks, but I rely on a borescope inspection more to determine the overall health of my engine. The picture of your oil on the dipstick looks normal to me. I rarely run my oil past thirty hours unless I am out on a trip, and I wait till I get home to change. Most oil gets pretty contaminated at thirty hours or so from that blow by combustion gas and to me oil is cheap... well it used to be, but that's another chapter. Oil analysis is a tool that is used to establish a base for your individual engine's health. You should get three or four consistent reports then monitor the elements for change. The drastic changes indicate something new is happening and you need to identify it and make a plan of action. If you are concerned with blow-by an above normal fuel presence would be an indicator but not the only sign. Each engine has its own proclivities when it comes to weaknesses that show up on an analysis report. I have an IO-360 in my 1968 Cessna Cardinal and like a lot of Pipers it has a cam corrosion problem if not flown often and because of the engine construction there is no way to borescope it to see what condition it's in. You stated you burn one quart every 13 hours and that's actually pretty good.
 
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