What does a cylinder leakdown test determine?

A cylinder leakdown test is specifically designed to assess the integrity of an engine's internal components, particularly focusing on whether air is escaping from the combustion chamber due to issues such as worn valves, piston rings, or cylinder walls. During the test, pressurized air is introduced into the cylinder at top dead center of the compression stroke, and any loss of air can indicate where leaks are occurring.

When the test reveals pressures or sounds indicating that air is escaping from the cylinder, mechanics can diagnose whether the source of the leak is from the valves or the piston rings. This makes it a critical tool for evaluating engine health and determining if repair or rebuild is needed.

The remaining options do not pertain to the primary function of a cylinder leakdown test. Fuel mixture efficiency, overall engine temperature, and oil pressure levels are assessed through different diagnostic methods and do not provide information on the condition of the cylinder's sealing components.