FAA Powerplant Written Practice Test

After the break-in period of a new reciprocating engine, what type of oil is typically recommended?

1. Straight mineral oil

2. Ashless-dispersant oil

3. Semi-synthetic oil

4. Single-grade oil

The correct answer is: Ashless-dispersant oil

After the break-in period of a new reciprocating engine, the use of ashless-dispersant oil is typically recommended because it offers a range of benefits essential for the proper functioning and longevity of the engine. Ashless-dispersant oil is designed to minimize engine deposits by keeping contaminants in suspension, preventing them from settling on engine components. This helps maintain engine cleanliness and efficiency, which is particularly important after the break-in period when the engine surfaces have begun to wear in and any debris from this process needs to be managed effectively. Additionally, ashless-dispersant oils are formulated to provide good thermal stability and oxidation resistance, which is crucial for the demands placed on an engine after initial operation. These properties protect the engine from wear and reduce the risk of sludge formation, ensuring optimal performance. In contrast, other oil types, such as straight mineral oil and single-grade oil, may not provide the same level of protection or cleaning ability, while semi-synthetic oils may be used in some applications but are not as commonly recommended immediately following the break-in period. Using an ashless-dispersant oil ensures the engine operates smoothly and efficiently as it continues to be used and subjected to varying operating conditions.