Who is correct regarding the engine oil specifications used in the summer?

Technician B’s statement about newer engines using 10W-30 oil is correct because many modern diesel engines are designed to operate effectively with lower viscosity oils, especially in warmer temperatures. This can enhance fuel efficiency and provide adequate protection under typical summer conditions.

In recent years, advancements in engine design and oil formulation have led to a transition in some applications from heavier oils like 15W-40 to lighter options like 10W-30. This choice can provide better performance and reduced friction at operating temperatures, which is particularly beneficial in summer conditions when engine temperatures can rise.

While Technician A asserts that all heavy-duty diesels use 15W-40, this is not universally applicable, as the recommendation for engine oil can vary based on manufacturer specifications, engine design, and intended application. Therefore, the idea that all heavy-duty diesels utilize 15W-40 does not reflect the current trends and specifications that include lighter oils for various engine types.

Choosing the correct viscosity oil based on the engine's specifications and operating conditions is vital for optimal performance and engine longevity, and Technician B’s assertion reflects a more modern understanding of those specifications.