Pistons are cooled primarily by transferring heat through which medium?

• A. Lubricating Oil
• B. Air
• C. Ring contact with cylinder wall
• D. Water cooling

Answer: (A)

Lubricating oil is the primary way the piston is cooled. The oil bath in the crankcase surrounds the piston and flows through passages that contact the piston surfaces, absorbing heat from the crown, rings, and skirt. This heated oil is carried to an oil cooler and then returns cooler to continue the cycle, removing heat effectively. Air cooling isn’t sufficient to cool the piston directly, and water cooling mainly removes heat from the engine block and cylinder walls, not the piston surfaces. The heat that does transfer to the cylinder wall ultimately ends up in the water jacket, but the piston itself relies on the oil to carry away most of its heat.