filter | Blackstone Laboratories

Oil Filter Inspection

Routine oil filter inspections are a useful tool in the aircraft owner’s diagnostic toolbox. We use spectrometers to test for metals on a microscopic level, smaller than you can see and smaller than an engine’s oil filter will remove from the oil. Larger pieces of metal that might not show up in spectral testing will be trapped in the oil filter. By checking the filter at each oil change, you’ll get a good idea of what normal is for your engine and be able to quickly identify any changes that might be the early signs of a problem.

Cutting the housing

In order to inspect the filter pleats, they must first be removed from the housing. While a hacksaw or angle grinder might get you there, we strongly recommend using a filter cutter to remove the lid of the filter housing. A filter cutter cleanly cuts the robust steel housing without producing metal shavings that might find their way onto the filter pleats you are about to examine. Plus, who doesn’t like a good specialty tool?

The AFC-470 from Airwolf Filter Corp is our go-to cutter here at the lab: http://www.airwolf.com/aw/products/oil-filter-cutter. This tool fits the filter from any Lycoming or Continental engine we’ve come across. Airwolf also offers a smaller cutter for Rotax engine filters. For those who might also want to examine filters from other engines, like their car or truck, filter cutters that cover a wider range of filter sizes are available from speed shops such as Summit Racing. (https://www.summitracing.com/parts/sum-900511)

Secure the filter lug in a bench vice. If the filter doesn’t have a lug, you can secure the lower section of the filter housing in the vice – just be careful to not crush the housing or it may trap the internal cartridge with the filter pleats. Poking a hole in the housing to allow oil to drain can also trap the internal cartridge, so we recommend avoiding that as well.
Place the filter cutter on the filter and gently tighten the cutting wheel. We like to take a conservative approach in cutting the housing, progressively tightening the cutting wheel over a few rotations, rather than trying to cut through in one pass.
Once the lid has been cut, the cartridge with pleats can be removed from the housing. It is also good to inspect the inside of the filter housing for metallic particles and other debris that may not be trapped in the filter pleats.

Removing pleats from the cartridge

You have two options at this point. You can use a solvent such as mineral spirits to wash debris from the pleats, leaving the cartridge assembly intact. The resulting solvent/debris slurry is then filtered for examination. In our experience, this flushing method may not always remove all of the debris from the filter pleats. We prefer to cut the filter pleats from the cartridge for examination by the following method.

Disclaimer: There is the potential to guillotine a finger or two during this process. Proper technique greatly reduces the chances of extensive cursing and an unplanned trip to the local emergency room.

Place the filter cartridge horizontally on the bench and hold with your non-dominant hand. Locate the filter pleat seam that adjoins the two ends, usually with a metal band or glue.
Hold the knife with your knuckles against the bench for stability. Starting at the seam and using only downward force, cut along the edge of the pleats opposite the side you are holding. We prefer to rotate the pleats into the knife blade, firmly holding the knife in a fixed position. This method, when done properly, protects your off-hand’s fingers from the knife blade, where the knife moves downward into the bench if it were to slip.
Flip the cartridge around and repeat steps 1-3 on the other side. You may have to make a few passes on each side to fully cut the pleats. Using a new razor blade helps.
Again locate the seam where the two ends of the filter pleats are joined together. Cut across the pleats on either side of the seam.
The pleats can now be removed for examination. If properly cut, the pleats will come out in one long piece with a clean edge on both sides.
The pleats will still contain a fair amount of oil at this point, making it difficult to see metallic debris. If time allows, you can place the pleats on paper towels to drain overnight. You can also squeeze the pleats like an accordion and mop up the oil that squeezes out with paper towels.

Inspecting the pleats and basic identification of common particles

Stretch the pleats out under a bright light or outside on a sunny day. Larger metal slivers will be obvious, but you may have to look quite closely to identify smaller particles. Here at the lab, we have a dedicated space with clamps that stretch the filter pleats out in one long section. You can improvise in the shop by placing something heavy on both ends of the pleats.

A strong magnet (covered with a plastic baggie or cling wrap) will remove ferrous particles from the pleats. We also suggest checking the pleats themselves with a magnet. Severe steel wear may generate enough small ferrous particles to make the pleats react to magnet.
Aluminum has a bright, silver appearance and will not react to a magnet.
Copper-containing alloys, such as brass or bronze, vary from a light straw to copper color and will not react to a magnet.
It is also common to find carbon, especially in the filters from turbocharged engines. Carbon is black, hard particles that can be broken apart between your fingers. A large amount of carbon might indicate excess blow-by, but what counts as excessive is unique to each engine. Regularly checking the oil filter will give you a good idea of how much carbon is normal for your engine. You might also find carbon with steel embedded in it, so it is good to check carbon particles with a magnet.
Small bits of sealer material may also be found, especially after repairs. We generally don’t worry about this sort of non-metallic debris.
You might also find lead deposits from fuel blow-by. These particles have a bright, foil-like appearance that can look very much like a metallic wear particle. These deposits can be distinguished from metallic wear by their soft and “smudgy” texture. It is worth mentioning that these deposits are not lead from the wearing surface of a crank or camshaft bearing.

Steel sliver

Aluminum flakes under magnification

Brass/bronze under magnification

Carbon deposit

Sealer material

Lead deposit

Evaluating Filter Debris/Conclusion

In some cases, a filter will contain so much metal that a looming problem is almost certain. But it is more often the case for the findings to land in an ambiguous gray area, where the severity of the metal is situationally dependent. You can expect to find some metal and other debris in the filter from a fresh overhaul, for example, where the same findings would be unusual in a routine filter inspection for that same engine at 500 hours since major.

Lycoming offers good guidance on the identification and evaluation of filter debris in Service Bulletin 480F. In our opinion, a lot of the information in that bulletin can also be applied to Continental engines. Blackstone also offers a filter and filter screen examination service as a compliment to oil analysis – but we recommend doing routine filter screenings yourself to get familiar with what’s normal for your particular engine. Save your money for flying — check your filter yourself!

Annual Inspection

Well, the building is over and my RV-12 is in the air. Now that I’ve got an airplane I can actually use to go places and have fun, life is a bit less hectic. Still, the fun has to stop sometime and for airplane owners, the opposite of fun is often the annual inspection. Since my aircraft is an experimental, I have to do what’s known as a condition inspection. There is maybe less paperwork involved than the annual inspection that certified aircraft have to go through, but the potential for pain is there. To be clear, this inspection is an extremely important thing to do and the pain will often be limited to just a lack of flying, though there is always the possibility that a major repair will be needed and then the pain can quickly spread to your wallet.

Inspection #2

I am actually on my second condition inspection. The first one was done in July of 2021 and it went really well. The airplane was new (only 26 hours on it), so there really weren’t any issues involving worn-out parts and other things that older aircraft have to deal with. Nope, just checking to make sure everything was working properly and all the fasteners were still holding fast.

This year has been different, but it’s not really the plane’s fault. My wife and I started the inspection in mid-July, when the weather was nice and there was still plenty of year left, but didn’t get it completely done until just last weekend (the end of January). Again, the plane is still fairly new (only at 46 hours now), so there really weren’t that many problems to address. No, this year the problem was with me. Life and work tend to have a way of keeping you busy and this year it’s been a struggle to string a few weeks together to do the inspection.

DIY maintenance

As many of you with experimental aircraft know, one of the perks of building an airplane is getting to do all of your own maintenance. No more having to find a mechanic and work around their schedule or pay their bills. The other side of the coin is, you have to do all your own maintenance. In fact, there isn’t a mechanic in this area that will touch an experimental aircraft, so I couldn’t hire this job out even if I wanted to. Thankfully, the work itself is pretty simple overall and the nice thing is there is a checklist to follow. These are printed in the maintenance manual and include a systematic checklist of everything that needs to be looked at.

I don’t think you have to be especially mechanically inclined or talented to do this job yourself, but a little mechanical knowledge probably helps. I took a 2-day class in Dallas to get a repairman certificate with an inspection rating. It was full of good information, but possibly the most important thing they did was show all the many ways people can die as a result of taking shortcuts and not following the checklist. By the time I was done with that class, I was fairly gripping the chair arms with white-knuckled fists, and ready to triple check to make sure I dotted all my i’s and crossed all my t’s.

Oil change at annual

The checklist has all kinds of things on it, and I can see how it might be tempting to skip something that seems unnecessary. One of the things on that checklist is normally an oil change. This is a standard part of most annuals and often times it’s done whether the oil actually needs changed or not. We see short-run samples like this all the time at Blackstone and often wonder if the owner is looking for a problem, or if the plane is just in for annual and this was on the list.

In my mind, if there was any one item on the inspection checklist that could be skipped, it would be an oil change that’s not needed (Blackstone’s lawyers would like to remind you that this is one man’s opinion only; officially, Blackstone advises you to follow the checklist!). Still, with that being said, an oil change is really an excellent diagnostic tool. You can send in an oil sample to see if the engine is wearing poorly and cut open the oil filter to see if it has any visual metal present. The problem with a short-run sample is, we can rarely tell the customers a lot other than there wasn’t much metal in the oil, so it looks okay from what we can see.

Unless you suspect a problem, a short-run filter inspection would also be of minimal value, for the same reason—there really isn’t enough time for any significant metal to accumulate. So how about a situation where you are halfway through a typical oil change? Where you have enough time on the oil for an analysis to tell you something, but not enough time that the oil really needs to be changed? For situations like that, you might want to get an oil sample by pulling one up via the dipstick tube. We sell a pump for just that purpose. It’s reusable and the money you’d save on an unnecessary oil change would likely pay for the pump in pretty short order.

Sampling from the filter

Or, what might be an even better option is to just change the oil filter at that point. Then you can pour an oil sample right from the filter and still cut it open to look for metal. If you do follow this route, just let us know you got the oil sample from the filter. We might see a little more insoluble (solid) material in this situation, but the metals and all other results should be basically the same as if you got the oil as it was draining out of the sump.

We understand there might be some situations where it’s not possible to stray from the checklist and it’s just easier to dump the oil and start fresh, though if you have some leeway in that regard, skipping an oil change can save some time and money, making a potentially painful job a little less so.

By Ryan Stark|2024-09-18T14:20:13-04:002023|Aircraft, Articles|Comments Off

Under Pressure! (Part 2)

In Part 1 of this saga, our flying club’s newly installed O-360 lost oil pressure in flight with a student pilot at the controls. After a brief landing then an immediate a go-around (you read that right), and a fair amount of sweat and tears – but fortunately no blood – we found the engine had digested an errant paper towel, which was blocking the suction screen.

Crud in the pan

The hard part begins

Now that we knew the engine actually did suffer a loss of oil pressure (it wasn’t just the gauge) and the filter analysis showed that some damage had been done, our next step was to figure how to proceed.

We consulted as many experts as we could and received suggestions ranging from “just go fly it” to “pull a cylinder and look for damage” to “overhaul it” and everything in between. The jury was out, and we had to decide whose suggestion to follow.

Lycoming has a convenient Service Bulletin about what to do if you find metal in the oil filter, so we started there. Service Bulletin 480F suggested, based on the amount and size of metal in the oil filter, that we remove the oil pan and check for metal. That seemed like a good idea; not only were we still troubleshooting mechanical wear, but also, we didn’t know how much paper towel was still in the engine.

It took two solid days of work to remove, inspect, clean, and reinstall the oil sump, which still had paper towel in it. Once that was done, after finding no large pieces of metal in the sump and being sure there weren’t any leftover paper towels in the engine, we did a 30-minute ground run then drained the oil, and cut the filter to check for metal.

Intestinal fortitude

The oil analysis was unremarkable, but the oil filter report noted 10-15 non-ferrous metallic flakes per pleat with a few dozen larger pieces that had scrape marks on them. So – a little better than

Metal from the filter, magnified in analysis

before, but certainly not clean. But this was only a 30-minute ground run compared to the 20-some hour sample. Were the improvements from the shorter oil change, or an actual improvement? We didn’t know.

Now, I’ve been an analyst at Blackstone for over a decade. I’ve helped countless customers diagnose their own engine issues and told people to go fly it and check back. But there isn’t any amount of intestinal fortitude that prepares someone for the reality of experiencing a problem, diagnosing engine damage, doing what you can to fix it, and know that the next step is to go flying and see how it goes.

The two A&Ps on the field agreed that if we made it past the first 10 hours (if) without any oil pressure issues, then we should be fine. “But watch that oil pressure,” they cautioned.

Going up

We took all the precautions we could: we went up in pairs (so one person could watch the oil pressure), we selected calm days, affording us four runway options for an emergency landing, and we stayed within glide distance of the airport for 10 long hours.

I am glad to say that those first 10 hours were uneventful. Oil pressure remained strong, the engine ran great, and we had no issues. With each hour that passed, our confidence grew, so we eagerly sent another oil and filter sample for analysis, hoping for hard data to bolster our confidence.

The oil analysis was unremarkable, but the filter – not great. Approximately 30 variously sized non-ferrous flakes were present per pleat, along with one piece of steel.

Not what you want to see

This wasn’t what we were hoping for, but this oil run was 10 hours long as opposed to the previous 30-minute ground-run sample. There was bound to be more metal, right? Regardless, there was still more metal after 10 hours than there was in our previous 50-hour samples, so we weren’t in the clear yet.

Our solution? Do another 10-hour oil run for an apples-to-apples comparison. At this point, with 10 hours of uneventful flying under our belt, our confidence was starting to grow, so we ventured out a little from the airport environment. After 10 hours, we sent the oil and filter for analysis, fairly confident that this second sample would reveal the improvement that was bound to come.

Instead, we received the disheartening news that “the overall quantity and size of the non-ferrous flakes was similar to the previous filter.” Dang.

Hard discussions

We debated what to do next. Are we throwing money away on oil and filters when we might need an overhaul anyway? Do we keep wasting filters when the nationwide filter shortage might ground us anyway? Do we run 25 hours, despite not seeing an improvement in the metals?

We reconsidered an earlier suggestion to pull a cylinder and look for crank/bearing damage, but that might raise more questions than answers: what should a 1500-hour crank/bearing look like? How will we know if the damage is excessive without pulling all four cylinders and comparing? And at that point why not just overhaul?

Opinions varied among our club members. One thought we were overreacting and that a paper towel couldn’t cause engine damage. Others of us were more cautious, remembering how little metal our engine used to make in 50 hours. As a group, we exchanged some vibrant text conversations as we decided how to proceed.

With our concern about irreversible, ongoing damage, we opted to do another short 10-hour oil change to try and limit further damage and get another good comparison to gauge progress. I was afraid that if this sample didn’t come back cleaner, we’d start considering exploratory surgery and watch the summer tick by from the ground.

Baby steps

We knocked those 10 hours out in less than a week and had results early the following week. I jokingly told my coworker that I’d bribe him with beer if he gave us a good enough report that we wouldn’t have to ground the aircraft for the summer.

Still with the metal

As it turned out, no bribery was needed: the oil analysis came back clean and the filter report contained good news: less metal than before. Finally! Maybe everything was going to be okay. Granted, we’re not totally out of the woods yet – we’re still monitoring and we’re going to change the oil in 25 hours, but at least we’ve got data that suggests we’re past the worst of it. If the numbers are good in 25 hours, then we’ll try 50. That night of the improved report was the best night’s sleep I’d gotten in months.

Lessons learned

Hindsight is always 20/20, as they say, but looking back I think there are several lessons to be learned.

First, when you’re troubleshooting a problem, do your research and get as much data as you can. It honestly shocked me how many different opinions we received. At one point I called Lycoming. They called me back several days later, and after listening to my story the tech said we needed an overhaul.

I replied, “Well in the week I was waiting for you to get back to me, we did a 30-minute ground run, tested the oil and filter, and we’ve since flown a couple of uneventful hours, as per SB 480 and we’re planning on flying a total of 10 hours before retesting.”

He said, “Okay, that’s good. Do that and proceed as planned.”

In less than five minutes he went from telling me to overhaul to “go fly.” There’s a vast dichotomy there. I get that there’s a lot of liability in aviation, but that just makes it harder to make good, educated decisions. We did a lot of research, gathered data, and consulted with as many people as we could to make the best decision for us. Do your homework.

Second, remember that you have many tools in your toolbox for diagnosing problems. Our oil reports came back clean all along – it was the filter analysis that was showing metal. Oil analysis measures the microscopic particles in the oil; the filter/screen is where you’ll see visible metal. Always cut your filter open, and use oil analysis in conjunction with other tests (like borescope and compression checks). The more data you have, the better decision you can make.

Third, as we said last time – trust your gut. If your intuition tells you something is wrong, don’t ignore it. But the reverse is also true: after all those hours of flying the pattern with strong oil pressure, good RPMs, and normal oil temps, we had a strong feeling that our engine was going to be okay – we just had to wait a few oil changes for the data to support our intuition.

And last but certainly not least – keep the damn paper towels far away from your engine!

By Amanda Callahan|2024-09-18T14:21:50-04:002023|Aircraft, Articles|Comments Off

Under Pressure! (Part 1)

About a year ago I started a flying club at my local airport with three other pilots – that was a long and interesting process that I won’t go into here – but after a few months of trying to get the right people together then struggling to buy an airplane in a hot market, we were able to purchase a 1965 Cessna 172 F with the Air Planes 180hp Lycoming O-360-A4M upgrade, with about 1300 hours SMOH. The pre-buy inspection went well and I had the honor (with another member) of flying our new ship home to Illinois from Florida.

As a 12-year analyst at Blackstone Laboratories, of course I did an oil and filter analysis as part of the pre-buy inspection. With that data in hand and considering how active our new aircraft was, we decided to proceed with Lycoming-recommended 50-hour oil changes right off the bat.

The first few oil analysis reports were excellent, and the oil filters came back nice and clean. The first time we pulled the oil suction screen we found a small amount of fibrous material in it, but the previous owner confessed that they hadn’t ever pulled the screen, so we assumed the debris was probably years – if not decades – old. We didn’t worry too much about it. When the next screen came back clean, save for a mere spec of carbon, we forgot about the fibrous debris entirely and happily went about enjoying our new bird.

Lost oil pressure

That is… until March 29th, when one of our newer student pre-solo members texted that, 10 minutes after takeoff, the engine lost oil pressure. He and the instructor landed without incident and reported everything looked ok, hoping it was a bad gauge.

The questions from the other partners streamed in: where were you? How was the engine running? How was oil temperature? The student pilot clarified: they took off to the north, climbed to 5,000’ to work on maneuvers, and when they did the cruise checklist they noticed the low oil pressure. He reported returning to the airport immediately with no issue. The engine ran great the whole time, and oil temperature was fine. No apparent oil loss.

I was out having coffee with a friend at the time, but my heart sank and I couldn’t focus on anything else, so she and I ended up going to the airport, with an A&P friend on the phone to look for something obvious, like an oil leak at the oil pressure gauge or where the line comes through the firewall. I didn’t find anything, but I wasn’t too discouraged: I knew we had a lot of things to troubleshoot before suspecting engine damage, so I tried not to jump to any conclusions.

Filter pleats with slimy debris embedded

Initial shock and investigation

The following day, our club maintenance director – under the watchful eye of our A&P – started working through the troubleshooting list. We quickly determined it wasn’t the gauge, and it wasn’t the line, so the easy, cheap fixes were off the table.

Now concern was starting to mount; the deeper we had to dig, the deeper our pockets were going to have to be. We’re a new club, already operating on a shoestring budget, so we didn’t have time or money for costly repairs. But we had a problem to solve.

The next step in our troubleshooting process was to start looking for a problem. We drained the oil, pulling an oil sample in the process, and we removed, cut, and inspected the oil filter. The only abnormalities were some clumpy, slimy looking lumps (see figure 1) and a giant piece of carbon (figure 2). The carbon was large enough to wonder if something similar had gotten stuck in the oil pressure relief valve, so we pulled the oil pressure relief valve off hoping for a big piece of carbon to be our easy culprit.

Much to my dismay, the oil pressure relief valve was totally clean.

Looking at the screen

Later that night, with the oil drained, the filter cut and the oil pressure relieve valve not the suspect, I pulled the oil suction screen. My heart sank. The screen was completely blocked by fibrous

Debris on the end of a fingertip

material. It looked like the same stuff we found in our earlier oil change, only a whole lot more of it. The pickup screen was so caked full that I had to use a screwdriver to pry the debris out of the screen (figures 3a and 3b).

That’s when concern really started to set in: we actually did lose oil pressure, and there could be some serious damage here.

A few days later the oil analysis and official filter report came back: the oil report was unremarkable, but the oil filter report was disheartening. Our engine had gone from making “no appreciable metal” in 50-hour oil change intervals to making “non-ferrous metallic flakes at an approximate rate of 20 pieces per filter pleat” in a matter of 20 hours. Great. Now what?

Fact-finding

The filter report stirred up more questions than it did answers. The next step in the process was to figure out how much damage was done, what that fibrous material was, how it got there, how much remained, and, most importantly, what to do next?

The fibrous material turned out to be the easiest question to answer – it was a paper towel. When examined under a microscope, it had the very distinctive dimpled pattern you see on “quilted” paper towels (see figure 4). Once we identified the contaminant, the next step was figuring out how it got there.

Fluffy stuff that came out of the suction screen

Interestingly enough, the previous owners provided the answer in the photographs they shared with me during the pre-buy. A couple of photos showed the process of swapping the original O-300 with the O-360. In figure 5 you can see a couple of paper towels sticking out the back of the engine where the magnetos should be. I believe that some (or all) of that paper towel somehow ended up getting stuck in the engine – either someone turned the prop and the gears pulled it in, or some of it got wet with engine oil and broke off into the engine.

**You did what?**

There’s another interesting twist to this story: as we were trying to figure out how long the engine ran with no oil pressure, we looked at the flight track on FlightAware. As reported, the plane took off to the north, climbed to about 5,000’ turned around then did a 360’ turn, presumably to lose altitude. Then there’s a normal approach to landing and…a go-around.

Wait, what?

That’s right – a go-around. With no oil pressure measuring on the gauge. When we confronted the CFI about the flight track, he confirmed: the student pilot was flying, and he came in too high and too fast to salvage the landing, so a go-around was initiated. *face palm*

Why didn’t the CFI take control of that flight and land? Because he assumed it was a gauge problem. Oil temp was fine, the engine was running well, so he didn’t worry about it.

Ground up paper towel under a microscope

The good news was that the CFI confirmed that oil pressure wasn’t lost entirely (as the student pilot had reported). It was only lost when at idle. If there was some power, there was some (albeit not much) oil pressure reading on the gauge. With that information, and knowing the engine hadn’t seized entirely, we were hopeful the engine damage was limited.

Moving forward

So, we’ve finally found the culprit, and now the long road to recovery begins. The main takeaway from this part of the story is, if you see anything unusual at all – anything – get on the ground as soon as possible. Don’t assume a low oil pressure reading is a bad gauge, and don’t fly when something might be wrong. Don’t dilly-dally, waiting for traffic to clear. Declare an emergency if you have to and diagnose with two feet firmly planted on terra firma.

Check back in the next newsletter as we discuss the confusing, gut-wrenching process of figuring out whether we could salvage the engine!

By Amanda Callahan|2024-09-18T14:22:01-04:002023|Aircraft, Articles|Comments Off

By-Pass Oil Filtration

Want to run your oil longer than you used to? Lots of people do. We take many factors into consideration when determining your optimal oil change. Many people think choosing the right oil is important, but in reality, you can run any API-certified oil indefinitely, as long as it’s not contaminated. That’s the real key: not contaminated, with metal, solids, moisture, or fuel. So what can you do to keep your oil in pristine condition? Enter bypass filtration.

In-line oil filtration — the oil filter that comes installed from the factory — filters oil entering the engine down to roughly 30–40 microns (millionths of a meter). This is about the most the in-line system can achieve, because when the oil is cold or the filter is partially plugged, a finer filter would cause too great a pressure drop, forcing open the filter bypass valve and allowing unfiltered oil to circulate through the engine.

Bypass filtration works differently. When this type of auxiliary system is installed, some of the oil bypasses the in-line filter system, flowing though a bypass filter and then returning to the oil sump. Using this method, sump oil is constantly being cleaned any time the engine is running, and it can be filtered down to a very fine size. All you have to do to maintain the system is occasionally change the bypass filter.

Bypass filtration systems remove blow-by and oxidation products from the oil and can help reduce silicon accumulations. Having a bypass filtration system installed increases the overall sump size of the engine, helping dilute the concentration of metals in the oil. Oil does not wear out. Its usefulness is limited only by contamination. Bypass filtration removes or dilutes many of those contaminants.

Is a bypass filtration system a good move for your engine? The only way to know is to test your oil. Send us a sample and tell us you’re considering adding a bypass filter. We’ll let you know what areas of the report might see improvements and whether those improvements would be essential to run longer on your oil. Bypass systems can be helpful, though not everyone benefits from a bypass system in the same way. In general, we have found bypass systems to be helpful in keeping the oil clean.

By Jim Stark|2024-09-19T10:21:01-04:002023|Articles, Gas/Diesel Engine|Comments Off

What are Insolubles?

The insolubles test measures the total insoluble materials in an oil sample — that is, all solid or liquid materials that are not soluble (won’t mix) in with the oil. We test insolubles using the centrifuge method. A measured volume of oil is mixed with a heated solvent, agitated, and spun at high speed. Insoluble materials collect at the bottom of a tapered glass test tube and can then be quantified. The insolubles level indicates how fast the oil is oxidizing and how effectively the oil filtration system is functioning.

Virgin oils shouldn’t have more than a trace of insolubles in them. The insolubles in virgin oils are from the normal oxidation process of the oil, which leaves free carbon in suspension when oxygen forms with hydrogen (oil is a hydrocarbon). Or they can be from additives that have fallen out of suspension.

Industrial oil normally contains a very low level of insolubles due to the few and relatively mild heat cycles the oil experiences (heat cycles accelerate the oil’s normal tendency to oxidize). Further, oil filtration on industrial machines may filter particles as small as 2 to 10 microns, keeping the oil pristine for a very long time, often years.

Automotive and aircraft oils however, suffer the most difficult environmental problems of all types of oils we analyze. They regularly receive blow-by products from the combustion process, and they suffer extreme heat cycles. Any contaminant will accelerate the oxidation process, causing insoluble materials to increase. Because excessive solid material in the oil limits the oil’s ability to lubricate effectively, an engine oil with a high level of insoluble material needs to be changed.

Excessive insolubles can form if the oil or engine is running hot, is receiving more than a normal amount of contamination or blow-by, is suffering more (or more severe) heat cycles than is normal, is being run longer than a typical use cycle, or, on the other side of the coin, if oil filtration is marginal or relatively ineffective.

If we found no contamination in your oil and your oil change intervals are normal, we often mention a problem at oil filtration as a possible cause of higher insolubles. Your oil filter may be inferior, or it is possible the oil filter bypass valve has relieved if the filter is becoming restricted. The filter system bypass may also open upon unusually cold starts when the oil is too thick to pass through the filter media. Once the bypass relieves, the filter is effectively out of the system.

The insolubles test is a fair measure of several possible problems in your engine. One high reading needn’t be a cause of concern. Several high readings in a row merit investigation of what the problem may be.

By Jim Stark|2024-09-19T10:45:32-04:002023|Articles, Lab Tests|Comments Off