🔍 Key Concepts

• Diesel exhaust valve operating temperatures in the exhaust port and at the valve head and stem • How heat is removed from exhaust valves (conduction through the stem to the valve guide and cooling system) • Purpose of sodium-filled hollow components in high-temperature engine parts

💭 Think About

• Think about what part of the engine the exhaust valve is exposed to and which stress is most severe: heat, pressure, corrosion, or weight? • Ask yourself what a liquid metal like sodium inside a hollow stem might do when it gets hot and moves inside the valve. • Consider which option directly relates to protecting the valve from its biggest source of damage during exhaust stroke operation.

✅ Before You Answer

• Identify which choice deals most directly with temperature and heat transfer, not just strength or corrosion. • Recall that sodium has a low melting point and high thermal conductivity—how would that be useful inside a hollow valve stem? • Verify which problem is more critical for exhaust valves in high-output diesels: overheating of the valve head or valve spring surge.