First of all, the suit says, some of the oil that enters the combustion chamber is burned off, which reduces the overall oil level in the engine and, consequently, increases the risk of engine damage due to improper lubrication.
Second, oil in the combustion chamber that doesn’t burn off may coat the spark plugs’ electrodes and keep them from firing properly or at all, the complaint says.
The unburned oil could also harden and cause carbon buildup, leading to pre-ignition detonation, commonly called “spark knock,” according to the suit. Spark knock, the case says, causes the piston rings to be unseated from their positions and wear out even more quickly and vaporizes the thin film of oil on the cylinder walls, causing it to be vacuumed into the intake manifold.
Further compounding the problem, according to the case, are oil spray jets that “overload[]” the piston rings with excessive spray, and the engine’s positive crankcase ventilation (PVC) system, which apparently vacuums oil from the valve train and ultimately feeds it into the combustion chamber.