Clean engine oil is essential to long engine life. Generally, service experience has shown that the use of the external full flow filter can increase the time between oil changes provided that the filter elements are replaced at each oil change. Under normal operating circumstances the oil should be changed every 50 hours, and the oil filter element should be replaced after each 50 hours of engine operation. It is very important that the filter element be cut open in order to examine the material trapped in the filter for evidence of internal engine condition. However, operation in dusty areas or cold climates may require more frequent oil changes despite the use of an oil filter. An engine which sits for long periods between flights should have an oil change at four month intervals regardless of the limited flight time accumulated. The filter cannot filter water and acids which may accumulate in the oil.
Oil consumption is a very important trend to monitor in an engine. The operator and maintenance people should know the general history of oil consumption during the life of the engine. It is typical of an engine during seating of new piston rings that oil consumption may be erratic or high; but after the rings are seated, generally within the first 25 to 50 hours, oil consumption should level off below the maximum limits established by the manufacturer. Later, during the life of the engine, if there is a noticeable increase of oil consumption within a 25-hour period (one quart or more per hr.), this could be a danger signal and calls for an investigation.
The oil screens and filter should be carefully observed for signs of metal, and maintenance personnel should take a compression check of the cylinders, preferably using differential pressure equipment, and also look inside the cylinders with a borescope or gooseneck light to detect any unusual condition.
THE AIR FILTER
The induction air filter is a very important element in the life of an aircraft engine. With the modern high performance powerplant, the operator must keep dirt and abrasives out of the engine if it is to attain the expected life and trouble-free hours. Although this is a maintenance responsibility, the pilot/owner should be aware that excessive wear and early failures of reciprocating engine parts is due, in many instances, to contaminates introduced through or around the air filter. The aircraft manufacturer’s instructions for maintenance of the air filter must be closely followed. When operating in very dusty or sandy conditions, it may be necessary to service the filters daily or every few hours in accordance with the airframe manufacturer’s recommendations.