How to Inspect the aircraft oil filter
 | Hold the oil filter - either in our oil filter holder shown here or in a vise as shown below
Our oil filter holder can be mounted in a vise or mounted to a work-bench. Just drop the filter into the holder and the nut engages into the hex and locks it into position. |
 | Vice mounted oil filter. You need to really tighten the vise to prevent the oil filter from slipping sideways. |
 | Squeeze and slightly rotate the can cutter to completely pierce the shell. Once pierced rotate the cutter 1 time around the oil filter. For automotive oil filters you can adjust the cutter depth by changing the set-screw on the handle. For smaller automotive filters you can move the rollers to the inside holes. |
 | Take some of the residue engine oil out into the sun and look at it with the sun shining on the oil. Look for any sparkles in the oil. Your inspection has be-gone!
This seems kind of a strange request but I have found that a bushing failure can result in many microscopic sized particles suspended in the oil. Sunlight brings out the sparkles. Under artificial light you don't see the sparkles. |
 | Lift the top off Notice the nice chocolate brown color. We know from the color of this oil that the engine has good piston ring compression. If it didn't the oil would be black - black like black lacquer paint. We also know that the engine has not operated for too long between oil changes as the oil would be darker than this. |
When I first started examining oil filters I would cut the can open and then cut out the paper filter media with a sharp knife. Aviation oil filters use thick tough paper and I thought eventually I would cut off a finger trying to cut out the paper media. A better and safer method is to place the filter media into a coffee can with some solvent (Stoddard solvent if you can find it) and shake well; This rinses the debris from the filter paper. Pour the solvent mixture thru a coffee filter and let dry. Drag a magnet under the coffee filter to separate out the iron from the rest of the stuff on the coffee filter.
Oil Filter Media Condition
Non-turbocharged: Tan colored, small amounts of hard carbon. Filter paper should not be brittle. Dark filter media without significant hard carbon means the filter has not been changed often enough. Dark filter media with significant amounts of hard carbon indicate high oil temperatures. Suspect compression blow-by, or poor engine baffle.
Turbocharged: Tan to dark colored with more amounts of hard carbon. If filter media is brittle then filter should be changed more often or oil temperatures should be reduced.
Things you might find -- Morphology
small aluminum slivers from the oil filter of a Lycoming O-320H2AD engine. Possibly from the piston pin plugs.
Here is where the aluminum slivers came from - the Lycoming piston pin plugs. All of them should look like the one on the left.
Chunks:
Dents and deformation indicate secondary damage has occurred when chunks wedged and jammed between moving engine parts. With secondary damage two or more separate damage sites may exist in engine. Evidence of fatigue markings indicates chunk originated from a primary failure point. Brittle fracture indicates impact failure from some other failed part. | Warning: any chunks larger than the oil filter pick-up screen will not be in the oil filter. Your oil filter is the second filter in the system. |
Melted:
Melted aluminum globules indicate preignition or detonation damage. Source is usually the piston.Slivers:
Small flat slivers are most likely tin or chrome. Probable tin source is washers. Particularly on Continental engines the rocker arm thrust washer is suspect. Usually not cause for concern. Cut and gouged slivers indicate metal on metal gouging. Source should be identified. Large amounts of bronze slivers in Continental engines is most likely from starter adapter gear. Continental IO-520AE doesn't use a bronze starter adapter gear.Platelets
Flat round steel slivers with possibly small cracks at the edges are from roller fatigue. Most possible source is camshaft lobes and camshaft followers. Chrome flaking off of chrome plated cylinders is another source for platelets.Machine marks:
Machine marks gives clues to the possible source.Carbon deposits:
Carbon or varnish deposits indicate the source was in a high temperature zone.Metallic:
Very small metallic particles found in the oil are best seen in bright sunlight. Take a oil sample out into the sunlight. Any small metallic particles such as microscopic particles of brass will reflect sunlight. Indoors the same particles may be invisible.
Oil filter analysis Links
Aircraft Oil Sampling and Aircraft Oil Filter Analysis
Why examining the oil filter and oil sampling may not give a true picture of engine condition
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