What is the primary purpose of a heavy, flat steel plate bolted to the oil pan rails?

The primary purpose of a heavy, flat steel plate bolted to the oil pan rails is to stiffen the crankcase to reduce torsional twisting. In high-performance or heavy-duty engines, ensuring rigidity is crucial for maintaining proper alignment and performance of internal components. The added stiffness helps to maintain the structural integrity of the engine under various operating conditions, including high revolution speeds and heavy loads. This rigidity minimizes the flexing and twisting that can occur during operation, which in turn maintains the correct clearances and promotes optimal engine function.

While preventing oil from splashing onto the cylinder walls, enhancing aesthetics, and serving as attachment points may have some relevance in engine design, the primary function of the steel plate is to provide structural support and stability to the crankcase, which is essential for the durability and efficiency of the engine.