since 1940

Why examining the oil filter and oil sampling may not give a true picture of engine condition

Nothing you see above will be detected using spectrometric oil analysis or examination of the oil filter because the pieces are too big to end up in the sample.

The oil filter is the secondary filter in the oil system. The engine has a screen that filters out large chunks of metal such as the ones above. For this reason the amount of metal in the oil filter is not representative of the amount of metal that may be in the oil sump.

The large dark pieces of metal above are from the connecting rod bearing. The black burnt appearance is typically of oil starvation to the connecting rod. Pilot reported that he had zero oil pressure a couple of times at idle. The rod bolts would have broke and the connecting rod would have flown out the side of the engine crankcase on the next flight. Whenever a loss of oil pressure is reported the engine must be grounded and the engine disassembled enough to examine the engine bearings.

The photo below shows a piece of bearing Babbitt found in the suction screen.

Badly spalled tappet from Continental IO-520 installed in a Cessna 210   Lots of pieces of steel have broken off the tappet. Now take a look at the oil analysis chart below  from this same engine. Only when the wear has become severe did the oil analysis start to trend up. By this time it's too late. The small pieces of steel have dinged the connecting rods and crankshaft. They have settled in the bearings where they are gouging the crankshaft; and they may lodge under the oil pressure seat face and prevent proper oil pressure. An examination of the oil filter would have detected this wear long before oil analysis did.

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