When engine oil exceeds the upper limit by 2 centimeters, the excess oil can easily enter the combustion chamber, leading to carbon deposits, increased resistance to crankshaft rotation, and excessively high oil pressure inside the engine. Carbon deposits: As carbon deposits accumulate, they can increase fuel consumption, clog the three-way catalytic converter, cause excessive exhaust emissions, and in severe cases, may lead to oil burning. Increased resistance to crankshaft rotation: This reduces the engine's power output, and the excess oil may enter the combustion chamber and participate in combustion, leading to oil burning, blue smoke emission, and even increased fuel consumption. The residue from burned oil (mainly composed of carbon, which is very hard) can accumulate on the walls of the combustion chamber, reducing its volume and thereby lowering the engine's compression ratio. At the same time, it can accelerate the wear of cylinders and pistons, reducing the vehicle's lifespan. Therefore, when adding lubricating oil, it is best to keep it slightly below the mark on the dipstick. Excessively high oil pressure inside the engine: Some parts sealed with oil seals may leak or become damaged. The most obvious is the valve cover. Overfilling with oil affects the engine's power output because the oil pressure can counteract some of the piston's power, making the engine feel sluggish.
