Plane & Pilot
Tuesday, October 22, 2013

Issues With Oil

Oil may be more important than fuel

I bought my first airplane, a Globe Swift, from a retired petroleum engineer and A&P mechanic who had lavished hundreds of hours on his airplane. In fact, he refused to sell it to me unless I agreed to maintain it his way.

Ed Kaston lectured me several times that the typical horizontally opposed piston aircraft engine is a complex mechanism with parts thrashing in all different directions, trying its best to tear itself apart. He explained that the only thing preventing that destruction was oil, and that the best preventive maintenance measure I could possibly take was simply to change the oil every 25 hours or three months, whichever came first.

He also suggested I not allow the airplane to sit for long periods of time without running it for at least 30 minutes around the pattern. That would bring the oil up to an adequate operating temperature to burn off the contaminants generated by lack of use.

I stuck to petroleum expert Kaston's advice religiously, even hired him to do the annuals, and true to his promise, the little 125 hp Continental ran perfectly for the eight years and 800 hours I owned the airplane.

Oil is no longer as cheap as it was in those days, but it's probably still the least expensive and most effective preventive maintenance measure I can take. Accordingly, I've become something of a student of aviation oil, and as a result, I change it every 20 to 25 hours, guaranteed.

In the perfect engine, oil would keep every part from ever contacting any other part. Without metal-to-metal contact, there would be essentially no wear, and a piston engine might last 5,000 to 7,000 hours or longer between overhauls rather than the typical 1,000 to 1,500 hours we see today.

In the real world, there's always some metal contact, because oil has a limited film strength. If two metal surfaces are thrown together with high enough temperature and pressure, even the best oil will break down, and the metals will begin to meet and wear.


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