Why do cylinder heads have coolant passages?

Cylinder heads have coolant passages primarily to remove heat from the combustion chamber. The combustion process in an engine generates a significant amount of heat, and if this heat is not effectively managed, it can lead to overheating, which may cause engine damage or reduced performance. The coolant passages allow coolant fluid to flow through the cylinder head, absorbing heat from the engine components and maintaining optimal operating temperatures.

By keeping the combustion chamber at the proper temperature, the engine can achieve better thermal efficiency, thereby enhancing overall performance and longevity. This heat removal process is vital for preventing knocking, maintaining the integrity of engine materials, and ensuring that the oil remains effective in lubricating the moving parts.

The other options, while relevant to engine operation, do not directly address the function of coolant passages in the cylinder heads.