🔍 Key Concepts

• Compression pressure in a diesel engine and what parts of the engine actually seal the air in the cylinder • The role of valves vs. piston rings/liner sealing rings in keeping compression from leaking out • Differences between problems that affect compression and problems that affect fuel delivery or cooling

💭 Think About

• Which components in the list are directly involved in sealing the combustion space so that compressed air cannot leak out? • Do issues with fuel oil pressure change the air compression in the cylinder, or do they affect something else? • Would low water in an expansion tank change the pressure of the trapped air in the cylinder during the compression stroke?

✅ Before You Answer

• Identify which options involve air sealing surfaces inside the cylinder (top, sides, and around the piston). • Separate options that affect cooling or fuel system from those that affect compression sealing. • Ask yourself: if this part failed, could air escape during the compression stroke and lower the measured compression pressure?