Bob Palamara: Oil Analysis Values And Ranges
I had my engine overhauled 3 years ago at Penn Yan and it runs great and uses about a quart of oil every 15 hours. When it was overhauled I opted for the Cerminil cylinders which saved about $2,000 and gave me a better warranty than new cylinders. I am now changing my own oil and have done 2 samples with Aviation Oil Analysis. The numbers are as follows (see text).
Bob, I have inserted the numbers I have seen over the past 7 samples, on my IO360. I burn (not leak or “blow out”) about a quart of oil every four hours, with 1,600 hours on a Zephyr Engines 1991 overhaul. The lowest oil consumption I ever saw was about 8 hours per quart, back around 1997-1998, with slowly increasing consumption since then. Based on six engines I once tracked, I believe that low oil consumption in a Lycoming or Continental is not necessarily a good thing (and especially not in Continentals, where cylinder wear is a serious issue). Aircraft engines have large clearances and rely on oil for wear reduction, sealing, and compression (along with cleaning, cooling, etc.). To a reasonable point, more oil is better than less, on the cylinder walls of an aircraft engine. My current engine compressions are the best they have ever been; 74, 76, 79 and 80 over 80. I would not have believed the 80 over 80, as I have never seen it before, but it has been recorded at two successive Annual Inspections, by three different people, using two different testers on each inspection (including one tester with the Continental-specified Master Orifice for calibration). I get no oil fouling on the spark plugs. I just pulled them for inspection and they remained fine, with virtually no deposits, at 250 hours on the set. I run slightly lean of peak, at peak, or 100 degrees rich of peak, depending on circumstances. I avoid operation in the range of 30 to 50 degrees rich of peak. When the overhaul was done, the original first-run cylinders were bored .010 per the Superior STC, and I have had no regrets; and have had no problems at all with the engine. I will have to make another cylinder choice on the next overhaul. Based on experience to date with the Lycoming factory steel jugs, that’s probably what I will use. I have described all this just to provide a relative engine benchmark to your engine’s cylinders, time, etc. You did not mention engine hours, and compression values.
You are not being given absolute ranges because there are so many variables; cylinder count, cylinder type, ring type, hours on the oil, type of oil, type of engine, turbo versus non-turbo, high or low-altitude aircraft ops design, type of air and oil filtering, typical ambient conditions, and more. The “range” for your engine is developed by four or five consecutive samples on your engine. Then the analysis watches for a sudden change; or an adverse trend over time.
I can’t pretend to be expert on the Cerminil cylinders. I believe that they are nickel plated (similar to the former chrome plating). Then, since the nickel doesn’t “wet” well with oil, a ceramic material is embedded into the nickel. It has the dual purpose of holding oil and resisting cylinder wear, while assisting with ring break-in. I suspect that the Cerminil cylinders also require the use of standard iron piston rings, rather than chrome-faced rings (as are used in uncoated steel cylinders). Because of the shop you used, and the low oil consumption (abnormally low for this engine, in my opinion), I’m pretty sure that the rings are correct for the cylinders. If chrome rings are used in coated cylinders, they usually fail to seat in, and cause high oil consumption.
The oil analysis outfit is probably telling you “it’s OK” because they suspect the nickel is from the cylinder plating and the iron is from the standard rings. Having said that, your copper and chrome also seem a mite high. It’s possible that your wear rates are a bit high due to too-low oil consumption on this high-output engine. On the other hand, if it only has 150 hours on it, it is probably still breaking in, and you don’t yet have an adequate number of samples over enough hours to see things stabilize. If you are not finding any significant visible material in the suction screen and filter media (other than the usual carbon granules), it is unlikely that there is a serious impending problem. Just take a sample every 50 to 100 hours, and make sure that the screen and filter media is getting examined during every oil change. Oil analysis is a useful tool, but in the absence of a trend history, and regular screen/media examination, it has a poor track record at predicting impending failures. You have to use all the available tools.
I hope that the numbers I plugged in don’t get scrambled in MML. Just in case, I am emailing you directly, and will post this on BAC.
|Element||Sample 1||Sample 2||My Norm||My High||My Low|
Values for Iron and Nickel were noted to be abnormally high. After I called the lab today and told them my cylinder material they now say that they are normal. Is anyone else out there doing sampling? Does anyone know what “normal” values are for this material? I contacted Penn Yan and also called ECI who apparently owns the process and neither had any numbers.
I/O 360 AIB