A combustion engine is subject to wear. Regular maintenance, such as timely oil changes, and a responsible driving style—such as allowing the engine to warm up gently and periodically applying sufficient load to reach high temperatures, thereby preventing internal contamination—contribute to a longer service life. As components become dirty or wear out, noises may develop, engine performance may decrease, or oil consumption may increase. There can also be cause-and-effect relationships. For example, unburned oil that ends up in the exhaust can cause damage to the catalytic converter.
When wear is suspected, a diagnosis can be made based on measurements. This can be done using external measuring equipment on the engine, such as a compression test with an oscilloscope (cylinder pressure measurement), as well as by inspecting disassembled components and measuring them with tools such as a caliper and a cylinder wear gauge.