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How often do you change your engine oil?





Let's answer this as it applies to the oils and engines in our two favorite toys, cars and airplanes.


You might be Interested to know that the auto manufacturers, as a group, define the quality of the oil required for their cars. They set all the performance standards for automotive oils. These include wear protection, piston deposits, rust protection, oxidation, fuel economy, sludge control, low temperature viscosity, oil consumption and catalyst protection.

You might be surprised to learn that the aircraft engine manufacturers have no input into the quality of the oils used in their engines. They simply approve the use of any FAA certified oil. And that certification standard is merely one of "Do No Harm". The current SAE spec, J1899, is still based on a WWII Navy Specification, MIL-L-22851 . Not exactly a modern high performance standard!

How often do you change the oil in your car? 3000 miles? 5000 miles? 10,000 miles? Do you know why? If you said 3000 miles, is it because you've that's what you've always done? And oil is cheap insurance. If you said 1 0,000 miles, is it because that's what the manufacturer says? If you said 5000 miles, is it because you feel it's a good compromise?

The auto manufacturers determine their oil change intervals based on a combination of three problems: One, the oil wears out (actually the additives get consumed.) Two, it does not hold its viscosity grade thru oxidation or polymer breakdown. Three, it gets contaminated with fuel and water. H the manufacturer sets the oil change interval at 1 0,000 miles for average use, they know that none of these problems will occur until well after this mileage.

How about your airplane?

How often do you change the oil?
25 hour? 35 hours? 50 hours? Once a year, at annual?
H you said 25 hours, is it because that's what your friends of the forums do? If you said 50, Is it because it's what the manufacturer or mechanic recommends? If you said 35 hours, is it because you feel it's a good compromise?

The aircraft engine manufacturers currently specify an oil change interval of 50 hours or 4 months with a full flow oil fitter or 25 hours or 4 months with an oil screen. Current filter technology offers nothing to warrant the doubling of the oil change interval.

Alters do not remove water, acids or the important 10 micron abrasive particles. There is no published information from either engine manufacturer that explains or justify this extension.

The Big Difference

Car engines are very different from aircraft engines. Car engines are water-cooled (radiators) and aircraft engines are air-cooled. This difference is crucial.
The reason is that air-cooled aircraft engines have large designed clearances between the pistons and the cylinder walls to prevent piston scuffing as the cold engine warms to operating temperature.

Water-cooled car engines do not require large clearances between the pistons and the cylinder walls because the of tight temperature control attainable because of water cooling.

This difference in cylinder/piston clearance is responsible for the dramatic increase in blow-by contamination of the aircraft oil. Blow-by is the small amount of combustion gas that squirts by the piston rings during every high pressure combustion event. Blow-by consists of unburned fuel, partially burned (and chemically reactive) fuel, water, and copious amounts of heat. And, when using leaded fuel, tiny lead bromide particles.



Aircraft Specialties Lubricants
2860 N Sheridan Rd. , Tulsa, OK 74115
Phone: 1-800-826-9252