What is the recommended engine oil for Truck 7?

The recommended engine oil for Truck 7 is SAE 15W-40 API CK-4 because it is specifically designed to provide optimal protection and performance for diesel engines, which are commonly found in larger fire trucks.

SAE 15W-40 is a multi-grade oil that performs well across a range of temperatures, ensuring that the engine is adequately lubricated during both cold starts and high-temperature operations. The API CK-4 specification indicates that this oil meets the latest performance requirements set for modern diesel engines, offering enhanced protection against wear, oxidation, and deposits, thus extending engine life and maintaining efficiency under heavy-duty conditions.

The other options, such as SAE 10W-30 API CJ-4, SAE 20W-50 API CD, and SAE 5W-40 API SN, may not offer the same level of protection or compatibility with the specific engine type or operational demands placed on Truck 7, especially if it regularly operates under stressed conditions typical of fire service vehicles.