It’s impossible to overstate the importance of regular oil changes. During engine operation, the oil becomes contaminated with nitric and sulfuric acids, water, lead salts, carbon, metal and other contaminants. It is essential to flush these out of the engine on a regular basis. In addition, the cleansers and acid neutralizers in the oil’s additive package wear out, and must be replenished. This can only be accomplished by changing the oil.
If your engine is equipped with a full-fl ow oil filter, you should change your oil and filter every 50 hours or less. If you have only an oil screen, you should change every 25 hours. In any case, you should change your oil every four months even if you have flown only a few hours during that time. The oil may look clean but the additive package is probably shot. In any case DO NOT EXCEED THE MANUFACTURERS RECOMMENDATIONS.
Whenever you change your oil, fly the airplane first in order to full operating temperature and to agitate any contaminants that may have settled out, back into suspension. Drain the oil as soon as possible after completion of the warm up flight to ensure that you drain out all of the contaminants. It is a good idea to drain the oil from the sump through a paint filter or similar strainer to catch any metal particles that may be in suspension.
Any particles found can be used in conjunction with any findings in the oil filter to determine the condition of engine. Insist that your mechanic cut open the filter and inspect the filter element for metal at every oil change.