A CLEAN ENGINE OIL ANALYSIS REPORT CAN BE FALSE “PEACE OF MIND” AND HERE’S WHY.

If you’re an aircraft owner, then chances are you’ve had an oil analysis done on your engine oil before. Why did you request an oil analysis? Was it recommended to you by another pilot, or your mechanic? Or, were you told that having an oil sample sent in for analysis will give you “peace of mind” that your rotating engine components are in good condition and not tearing themselves apart? There is this preconceived notion that getting back a clean oil analysis report means your engine is not producing metal and is in good condition. I have learned that clean oil analysis reports can give you false “peace of mind” and here’s why.

In my years of maintaining general aviation aircraft, I’ve probably sent in hundreds of oil samples. It was such a good feeling to get clean results back. You may have felt that before. It always gave myself and the aircraft owner the “peace of mind” we were looking for…until the one oil sample that completely changed my perspective on engine oil analysis. 

A few years ago, a customer came in for an oil change. With the owner present, I cut the filter open and found the most metal I’ve ever seen a Lycoming engine produce. I pulled the sump screen and found very large chunks of metal. It was clear that this engine was destroying itself and was unairworthy. The owner said, “Hey, let’s send in an oil sample so we can get a report of what type of ferrous or non ferrous metal this is.” I replied, “That’s a great idea!” So, with a stupid grin on my face and giggling with excitement, I collected the very large chunks of metal from the sump screen and piles of pulverized metal from the oil filter, and poured them into the clear sample container. The oil sample looked like a glitter bomb. I was already imagining what the sample report would look like: spiked bars in the bar graph, red flags everywhere, that big 4 letter word, “STOP!” I waited impatiently for the results. 

A week later, the results were in: “ All clean, no unusual wear or abnormalities.” I thought to myself, this must be some kind of a mistake. Surely they gave us the wrong oil analysis report. I called them on the phone and explained the situation. They put me on with the technician who performs the oil analysis tests. He verified and assured me that it was the correct oil sample that was tested, and the report was accurate. All of my “peace of mind” assurances were just thrown in the trash. I asked the technician, “How is this possible? Help me understand how this is a clean oil sample?” The technician explained the process to me. 

In a rough and dumbed down way so that I could understand, the technician explained; the oil sample flows through a glass tube and passes by a camera that counts metal particles towards the parts-per-million count, and the size of particles counted are 6 microns in diameter and smaller. Let’s put that into perspective. Imagine the size of 1 human red blood cell. A single blood cell is 8 microns in diameter. So, pieces of metal 6 microns in diameter and smaller were counted (smaller than a single blood cell) and the larger chunks of metal passed by the camera without being counted. The camera only counted those microscopic pieces of metal! My customer’s oil analysis report came back clean because the sample contained larger pieces of metal and not those tiny pieces the camera was looking for. My mind was blown.

The technician said they still had the sample and could offer a more advanced analysis that would consist of them putting the sample under a microscope and physically counting with the human eye. Then they would physically measure the size of the larger particles. We accepted. The advanced analysis report was much more accurate, represented the oil sample very well, and was very detailed. It included full descriptions and close up pictures of the chucks of metal in the sample. That is what we were originally expecting. 

Looking back at my history and experience taking oil samples for customers, I came to the conclusion that the knowledge available to us about oil analysis isn’t enough to understand the analysis process let alone decide which process is right for your engine. Allow me to explain. You and I first heard of oil analysis testing through the aviation community we reside in. You and I both probably went to Aircraft Spruce’s website and ordered the oil analysis kit for the first time. The oil analysis kits on the website give a general overview of the product. Who wants to research more than that? Reading the general overview about the product gave me “peace of mind” that this oil analysis kit will tell me if my customer’s engines are in good health or in need of attention. That was my mistake. I should have done more research. 

There are several companies out there that offer aviation oil analysis kits.They have great websites that offer much more information about their product, the process, and which oil analysis is right for you. By researching their websites, I learned a few more things I didn’t know that would have helped me understand a little more about the process. As an example, the differences between Oil Analysis and Oil Filter Debris Analysis. Oil Analysis only monitors the fine particles that are suspended  in the oil. Oil Filter Debris Analysis monitors the larger wear particles that are trapped by the filter. When oil analysis is combined with oil filter analysis, all of the various wear particles and sizes can be counted and reported. 

Now, with this knowledge and understanding of the oil analysis process, I can explain to my customers what is the real function and limitations of the standard oil analysis kit you can buy. I can also give them options of a more advanced oil analysis service these companies have to offer. If you have been sending in oil samples religiously, and have developed a wear pattern history, my advice to you is to keep doing it! Keep sending in those samples and keep the trend going. Just be aware of what the limitations are of the standard oil analysis kit. If you want a better “peace of mind” that your engine is in good health, order the more advanced kits and send in filter samples. Understand the possibility that your engine may be producing metal and the standard kit may not detect a problem. 

I had a recent customer come in for a cylinder change. When I removed the cylinder, I discovered the camshaft and lifters were heavily damaged from spalling. The engine was toast. I notified the owner and he was very upset to find out his engine was done for. What a gut punch. He asked me the question, “How the heck is my engine making metal?? I take oil samples every oil change! They’ve all come back clean! That doesn’t make any sense!” I had the answer to his question.