🔍 Key Concepts

• Expansion tank function in a closed cooling system • How combustion pressure could enter the cooling system • Which engine parts separate combustion space from coolant passages

💭 Think About

• Which component, if damaged, provides a direct path between the high‑pressure combustion gases and the engine’s cooling water passages? • For each option, ask: does this part normally see combustion pressure on one side and coolant on the other? • Eliminate choices that would more likely cause oil–water mixing or loss of compression without pushing gas into the expansion tank.

✅ Before You Answer

• Identify which option has coolant on one side and combustion chamber on the other • Check which failures would show up as coolant in oil or oil in coolant instead of gas in expansion tank • Confirm which part, if cracked or leaking, would let compression or combustion gases enter the water jacket directly