Which valve is commonly filled with sodium to improve heat dissipation from the valve stem?

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

Answer: (C)

When a valve handles the hottest gases, moving heat away from the valve head is essential to prevent overheating. Some exhaust valves are designed with a hollow stem that’s filled with liquid sodium. Sodium conducts heat very well and remains liquid at engine temperatures, so it circulates heat from the hot valve head up the stem to cooler regions where it can be carried away by the valve guide and into the cooling system. This convection-based heat transfer helps keep the exhaust valve from overheating and reduces the risk of damage to the valve, seat, or stem under demanding use.

Intake valves don’t run as hot as exhaust valves, so they don’t typically need this sodium-filled stem. The valve spring and rocker arm aren’t involved in this heat-transfer mechanism, so they aren’t equipped or used this way.