What is the purpose of a compression gauge?

A compression gauge is a specialized instrument used to measure the pressure within the combustion chamber of an engine when the piston is at the top of its compression stroke. The primary purpose of this measurement is to evaluate the condition of piston rings and the overall health of the engine's compression system.

When the piston moves up during the compression cycle, it seals against the cylinder walls, and the compression gauge indicates how much pressure is built up in that sealed space. Low pressure readings can indicate that the piston rings are worn or damaged, potentially leading to inefficient engine performance due to loss of compression. This makes the gauge a vital tool for diagnosing engine problems related to wear and tear or improper sealing.

The other choices involve different aspects of engine performance. For instance, measuring oil pressure relates to lubrication and engine oil health, which is not the function of a compression gauge. Checking spark plug performance focuses on ignition efficiency, while assessing fuel mixture quality is about fuel delivery and ratios, neither of which are related to the function of a compression gauge. Thus, the understanding and use of a compression gauge specifically center on evaluating the condition of piston rings.