Choosing & Maintaining the Right Engine Oil for Aviation Performance & Protection

It is accepted wisdom that your engine will last longer if you change the oil frequently. What the heck does “frequently” really mean? Engine manufacturers have their recommendations, which are sometimes hard to find and even harder to follow. 

What do they recommend for the typical aircraft owner?

There is no good answer for what the oil change interval should be for a super low-usage aircraft, like one that is only flown 20 hours a year. I would not expect this owner to change the oil every four hours. But going four years without an oil change will probably result in a ruined camshaft and other problems.

Instead of worrying about the tiny bits of metal in the oil, which show up at analysis- your engine is on analysis, right?-we really should be worried about corrosion. While modern aviation oils do a good job of lubricating and are good at minimizing corrosion, combustion byproducts eventually overcome even the best oil chemistry. Corrosive acids can start showing up in as little as 20 hours of operation. After 20 hours, the oils chemical equilibrium shifts to a corrosive environment.

Short of changing the oil, the presence of contaminating chemicals and water is the main reason piston aircraft engine gurus urge pilots to make sure their oil is heated up when flown. An ideal oil temperature is 180 to 190 degrees F, which helps drive off water and minimizes its ability to react with contaminants and form the acids causing corrosion. The real problem here is that this is not a rare occurrence in general aviation

Tearing down this TCM O-470, disassembly is extensive- particularly on these bigger engines. There are a lot of steps required to ensure that we preserve the engine parts and detect any issues that might cause us grief later during assembly. As much as we enjoy the builds, teardowns are pretty interesting, and you get a comprehensive picture of the engine’s life. We can tell most of what an engine has been subjected to just by looking at the state of the components, from overspeeds down to even the quality of engine oil that was used. 

It all leaves a mark.

This particular engine was in a Cessna 182, and the owner came to us for diagnostic help when he noticed metal indications in his oil. We determined the cause of the indications to be cam failure. Upon disassembly, we noted that the camshaft, tappets, and many other engine components showed significant signs of corrosion, not normally present. 

The oil brand they were utilizing has been problematic for engines that get intermittent use because the detergent neutralizes after a short period and eventually turns acidic. If oil changes are infrequent (periods longer than 25hrs or 4 months), this and water can eventually lead to corrosion. 

This was an older series O-470 and parts were difficult to source so we did a lot of in-house repair on drive train gears, connecting rods, and rocker arms. The customer elected for a complete overhaul and a new camshaft, lifters, bearings, and six new CMI Nic3 cylinders were installed.

An expensive repair (overhaul), which likely could have been avoided with either a different engine oil and/ or by doing more frequent oil changes. Proper servicing matters, and makes a huge difference in extending the running life of an engine, and the preservation of components for future overhauls. 

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