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What happens if you don't change your engine oil?

nigelspeedy

nigelspeedy

Well Known Member
My engine is fitted with a filter so by rights I could change the oil at 50 hours but given that it is the single most expensive part of the plane changing it at 25 hours seems like a reasonable idea. Since new I have sent a sample away for analysis. Well all good intentions but SnF came up when I had 20 hours on the oil and I was in a rush getting ready so I pressed on to 50 hours before the next change. Turns out engine oil gets dirty as you can see in the attached plot. Pretty normal but the second to last sample is the one with 50 hours on it then back to normal with a 25 hour change at the end. So I guess the good news is that even small changes are picked up. What I am not sure of is the major source for each of the different metals detected. Seriously where does Lycoming use Silver in an IO-360?
So for my continuing education and recreation where does the majority of the metals come from.

While the graph for an individual engine will show variations from its normal state are there any published absolute limits for these engines?

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Cheers

Nigel
 
Silicon

SI=Silicon

Elemental silicon also has a large impact on the modern world economy. Most free silicon is used in the steel refining, aluminium-casting, and fine chemical industries (often to make fumed silica).
 
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Do analysis companies "pro-rate" the results depending on how many hours you have on the oil? It seems like the more hours on the oil, the higher the readings would be. In other words, if you only have ten hours on your oil, do they multiply the numbers by 2.5 to normalize them to 25 hours? Conversely, if you have 50 hours on the oil, one would expect the numbers to be higher across the board, so do they divide them by 2 so that they're comparable to a normal change interval? The reason I'm asking is one of my reports had the comment, "Wear metals improved for run time." Inquiring minds want to know what this means.
 
I usually use Blackstone, and they give you a baseline to compare to with 35 hours, I think. They don't adjust your numbers. If you send in a sample with only 10 hours, they will usually make a comment about that.

Silicon is usually a reflection of how well your air filter is working. High silicon means it's not working well. It's basically dirt.

As for higher numbers after 50 hours, the numbers are close to the same amount per hour, so I wouldn't worry too much about it. If the engine sits, then corrosion internally can cause high numbers in a short number of hours, or more likely the first minute of running after sitting as it scrapes the rust of whatever is rusty.

I try to always change my oil every 25 hours and sometimes do the filter every other oil change. The oil breaks down and becomes less lubricative (is that even a word) over time. Oil is cheap, engines are expensive.
 
+1 on silicon - it is an indicator of how long the ring/bores will be lasting. One exception though, RTV (silicone) seems to drive up the silicon reading when used as a sealer, at least for a while. My guess is the sand at SNF got sucked into the intake. Silica dust can float for a while. Lots of wind and activity. Taxi lines etc. Drove up Fe and will drop again.

Wear particles are generally abrasive and effectively create a slurry that grinds away sliding things, and bearings when starting. Think like abrasive slurry honing. Look up extrude hone. It is a slow acting process so probably does not make much difference in 2000 hrs, but does have its effect.

The sump oil particles will rise with time, until the filter causes it to plateau. The oil filter is only about 30 micron (not an absolute thing) so it is always passing something. The idea is the passing particles are smaller than the oil film thickness in the bearings.

Long term oil use is more about total base number TBN. The additives ability to prevent acidification of the oil from sulfur and combustion gasses. Also look up oil oxidation. It is the thickening of the oil due to breakdown at temperature of the oil.

On highway truck engines are pushed to the limits to keep them on the road and not in the shop with oil changes. As high as 1000hrs (large sumps). They will track all the parameters, many more than touched on here. There are many many articles on oils from fleets. They have experimented with micron bypass filters and centrifugal filters for decades and many stationary long life engines use them 100%. This keeps the wear particles way down and they will supplement the sump oils with additives to keep up the base numbers.

Deere, Cat, Cummins all have their own oil analysis services. Typically lower cost than Blackstone, but no advisory services are available for our application.

Bobistheoilguy.com had the best information in the past, not sure about today. Too popular. Try the link it is a pretty good summary.
 
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nigelspeedy said:
Seriously where does Lycoming use Silver in an IO-360?
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I'm sure you know perfectly well that silver is Ag. I don't know for certain, but I seem to recall reading that the main bearings have some. I could well be wrong.
 
While Most Elements Listed are Typically Found in Steel...

Copper is an interesting one and has been previously discussed on the forum. The production of camshafts typically involve a copper plating/flash that is scrubbed off the bearing surfaces before case hardening - allowing those surfaces to accept the case while preventing penetration on the rest of the part. Some oils (Aeroshell 15W50) have agents that tend to leach the remaining copper off of the camshafts, resulting in spikes showing up with oil analysis. Apparently, you're not using the Aeroshell.
Silicon has been well covered in previous posts.
As far as residual silver - I don't have a clue.
Terry, Part Time CFI, Part Time Metallurgist, Full Time Forger
RV9A N323TP
 
You want to know where the Si comes from Nigel? Climb out from Mojave and look around....it's ALL Silica...... :)
 
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Oil

At 25 hours I'm down a quart and a half . Instead of adding I pump out the remaining 5-1/2 quarts and refill with 7 Fresh . At 50 hours it gets drained , screen checked and new filter . Cheap way to have fresh oil constantly
 
You might try running at 6 qts. instead of 7. Many engines throw out a quart if over 6.
 
Mel said:
You might try running at 6 qts. instead of 7. Many engines throw out a quart if over 6.
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They're called Lycomings, Mel :)

Years ago I spoke with a friend who worked sales for Lycoming. He told me to run the engine between 5 and 6 quarts. Anything above 6 will get thrown out. That was 10 years ago. I've run the engine between 5 and 6 ever since. I add a quart about every 13-15 hours to get back to 6 qt. The belly stays pretty clean.

Chris
 
I have to add 7 qts to an empty sump to get to the 6 qt mark on the dipstick. But, anything over that does indeed end up on the belly, so I don't fill beyond that mark.

Chris
 
Absoulute value limits for contaminants?

Anyone have any absolute values that can be used as limits for the various contaminants in Lycoming engines?

Cheers

Nige
 
Your engine is producing a pretty stable amount of metal. Each healthy engine will make a certain quantity of metal per hour due to wear, variable on factors, such as RPM, load, number or starts per hour, etc.

You should to expect to double the quantity of metal in your oil if you double the run time on the oil. It's not that the extended usage interval caused the metal wear, but that the oil was there twice as long to collect the metal the engine was producing. Your engine produces about 1 PPM of iron per hour. Therefore, a 25 hour interval will show ~25 PPM and a 50 hour interval will show 50 PPM.

I am not advocating extended oil changes, but not for metal reasons. Generally, it is the fact that lead and soot will, at some point, overload the oil's ability to hold it in suspension and it will deposit the excess in the engine as sludge once you reach this saturation point.

Larry
 
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duration of time

You also have to consider how long does it take you to fly 25 or 50 hours. I've easily flow 25 hours in a couple of weeks at times and at other times in the past when I flew a gas guzzler and fuel was $7 to $8 per gallon, I flew 25 hours in a year.... Obviously the time span has to be considered.
 
BCP Boys said:
You also have to consider how long does it take you to fly 25 or 50 hours. I've easily flow 25 hours in a couple of weeks at times and at other times in the past when I flew a gas guzzler and fuel was $7 to $8 per gallon, I flew 25 hours in a year.... Obviously the time span has to be considered.
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I follow Mike Busch's recommendation: 50 hours (with filter) or 4 months, whichever comes first.
 
turbo said:
sounds like the 6 qt mark is actually the 7 qt mark now. :eek:
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airguy said:
Remember that you're filling the new oil filter too.
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Yep, I fill the oil filter as much as possible when installing it, so that accounts for probably .5qt - I may end up a tad over the 6qt line on the dipstick, but after that it generally stays right at that line for 20-25 hours before I need to add anything.

In any case, not too worried about dipstick accuracy because I know how much goes is and how much comes out (not much).

Chris
 
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