Coking occurs when lubricating oil is exposed to temperatures high enough to thermally degrade the base oil, leaving behind a hard, abrasive carbon residue. This process typically happens in high-heat zones like turbocharger bearings or exhaust valves. The resulting deposits block oil passages, restrict heat transfer, and act as an abrasive that accelerates wear on mating surfaces.
Heard on the job
The turbo bearing coked up because the operator shut the engine down hot without letting it idle first.
Insider tip
Coking is often caused by hot shutdowns. Letting high-load equipment idle for a few minutes allows cooler oil to circulate and carry heat away from critical bearings before the flow stops.