What is specified for oil tank filler markings in piston engine powered airplanes?

The correct response focuses on the requirement for clear and comprehensive markings on oil tank fillers in piston engine powered airplanes. According to aviation maintenance standards, it is mandated that the oil tank filler must be clearly marked with the word "OIL" to ensure that individuals servicing the aircraft can easily identify the correct fluid to use. Additionally, it should reference the permissible grades of oil that can be utilized in the engine. This information is crucial as it helps prevent the use of incorrect oil types, which could lead to engine damage or failure.

Proper labeling enhances safety by minimizing the risk of mistakes during maintenance or operations, ensuring that only suitable oil grades are added to the engine. Markings that include both "OIL" and guidance on acceptable oil grades play a vital role in promoting compliance with manufacturer specifications and maintenance practices.

Other options do not meet regulatory standards or safety practices in aviation. For instance, having only the word "OIL" would lack the crucial information about acceptable oil grades, leading to potential misuse. Not requiring any markings would create confusion and could compromise safety. Similarly, requiring the grade of oil to be painted on the top of the engine does not provide the convenience and clarity needed during refueling operations at the oil filler location.