What factors must an engine manufacturer consider when determining the proper oil grade?

When determining the proper oil grade, engine manufacturers need to consider operating load and temperature as crucial factors. The oil must be suitable for the specific conditions under which the engine operates, including the loads it experiences during various phases of operation (such as takeoff, cruise, and climb) and the temperature ranges it will encounter.

A higher operating load may require an oil with enhanced lubricating properties to withstand the additional stress, while different temperature ranges can affect the viscosity and flow characteristics of the oil. Oils that are too viscous in cold temperatures may not flow adequately, leading to inadequate lubrication, while oils that are too thin in high temperatures might break down and fail to protect engine components effectively.

In contrast, while factors like altitude, humidity, engine age, model, fuel type, and ignition systems do play a role in engine performance, they are not primary considerations for selecting the oil grade itself. Hence, focusing on operating load and temperature directly addresses the physical demands placed on the oil in the engine.