Aviation From My Rocking Chair: Check Your Oil, Sir?

Hello again Troopers and welcome to a new installment of: “Aircraft…it’s a sickness.” Let me see a show of hands. How many of y’all maintain an Oil Analysis Program on your aircraft engines, transmissions, or gearboxes? Come on, put’em way up. Wow! Looks like I have some ‘splaining to do. Oil analysis is the evaluation of lubricating oil and any contamination that is present in a sample. It can be performed on any component lubricated by an oil bath or closed lube system. Did I hear someone ask, “What is involved in testing an oil sample? Thank you for the question and let me try to explain the process, and along the way, provide some other useful information.

Oil analysis is only part of an oil monitoring program. Particle analysis and filter analysis are also included. I’ll take them one at a time.

(1) Oil analysis:

a) Viscosity- Measures the thickness of the sample against new oil specifications. Helps determine condition of oil and is an indicator of water contamination and oxidation.

b) Water content - Detects water content greater than 1%.

c) Spectroanalysis- Tests oil for metal content and additives. Checks 19-23 elements (depending on type of tester used) and reports them in parts per million (ppm). Used to check for bearing or bushing wear in the form of copper, lead, or tin. Also looks at dirt levels in the form of silicon. Oil additives can be identified and evaluated. Note: Spectroanalysis will not detect particles in oil larger than 5 microns (25 microns=.001”). (2) Particle analysis:

a) Particle count- The most important test for filtration efficiency. Measures all particulate jn oil larger than 5 microns, including dirt, carbon, metals, fiber, etc. Can determine size, quantity, distribution, and identity of elements found.

(3) Filter analysis-a) Used to determine system cleanliness, predict component failure, and determine the source of contamination (internal or external).

b) Checks particles picked up by the filter or screen, usually 25-100 microns in size (40+ microns for a standard screen).

O.K., we have covered some of the tests done on an oil sample/filter, so let’s look at how a sample is taken: (1) As oil analysis is based on trends established over time, oil samples should be done at each oil change. (2) Run engine or component to bring oil to normal operating temperature.

(3) Be sure to let about a quart of oil drain before taking a sample. This will limit contamination from the bottom of the oil sump.

(4) Never take a sample out of the drained oil container.

(5) Cut open the old oil filter and inspect for contamination.

(6) You will receive a written report from the testing facility for each sample sent in. If you have more than one engine or component being tested, make sure the reports are kept in a separate file so trends and especially spikes in particle counts are attributed to the correct component.

Let me cover a couple more things, and I’ll let you go for another month.

(1) If you find particles of something in your oil filter or screen, you might try these tests to determine what it is:

a) Does the particle feel hard? If not, it could be fiber from external sources, like rags. b) A strong magnet will indicate ferrous metal such as steel.

c) Magnesium will flare when exposed to fire.

d) Tin will melt when exposed to fire.

e) Aluminum will fizz when exposed to Muriatic acid (HCL).

(2) A good oil sample program should find problems before they end in catastrophic failure, but if your filter shows a large amount of metal contamination, GROUND the aircraft until the source is determined. Finally, oil sample kits cost $22-$43. If you change oil and filter at 25-hour intervals, it will cost you $88-$172 per 100 hours. I think this is cheap insurance, don’t you?

Well, troopers, I’m shuffling back to my rocking chair, and cogitating on what I can come up with next month. Google is a tough act to follow!

Rick Vaux TC4130