What does a cylinder compression test evaluate?

What does a cylinder compression test evaluate?

• A. Oil pressure in the crankcase
• B. Compression pressure to assess valve seating, piston rings, and cylinder condition
• C. Fuel flow rate
• D. Airflow through the intake manifold

Answer: (B)

Cylinder compression testing checks how well each cylinder seals when the piston compresses the air-fuel charge. By measuring the pressure produced in each cylinder during a crank, you learn about valve seating, piston ring wear, and the overall condition of the cylinder bore. If the readings are within spec and similar across cylinders, the engine seals are solid. Low readings point to leaks or wear, such as worn rings, burned or mis-seated valves, or a head gasket problem. A wet test—adding a little oil into the cylinder and rechecking—helps distinguish ring leakage (compression should improve with oil) from valve or head-gasket leakage (little to no improvement). This test is focused on sealing performance inside the cylinders, not on oil pressure, fuel flow, or air flowing through the intake.

Cylinder compression testing checks how well each cylinder seals when the piston compresses the air-fuel charge. By measuring the pressure produced in each cylinder during a crank, you learn about valve seating, piston ring wear, and the overall condition of the cylinder bore. If the readings are within spec and similar across cylinders, the engine seals are solid. Low readings point to leaks or wear, such as worn rings, burned or mis-seated valves, or a head gasket problem. A wet test—adding a little oil into the cylinder and rechecking—helps distinguish ring leakage (compression should improve with oil) from valve or head-gasket leakage (little to no improvement). This test is focused on sealing performance inside the cylinders, not on oil pressure, fuel flow, or air flowing through the intake.