May be sodium-filled to dissipate heat.

• A. Intake valve
• B. Valve spring
• C. Exhaust valve
• D. Rocker arm

Answer: (C)

Sodium-filled valve stems move heat away from the hot valve head by using liquid sodium inside the stem to conduct heat to cooler parts of the valve assembly. The exhaust valve is exposed to the hottest gases, so it benefits most from this cooling method, making it the common choice for sodium filling. Intake valves run cooler, so they don’t require this extra cooling as much. Valve springs and rocker arms are separate components and don’t use sodium-filled stems for heat dissipation.