Which color of smoke indicates excessive fuel burning in the combustion chamber?

The presence of black smoke indicates excessive fuel burning within the combustion chamber. This occurs when there is an imbalance in the air-fuel mixture, typically resulting from an overly rich mixture where too much fuel is supplied compared to the amount of air. This situation leads to incomplete combustion, where not all of the fuel is burned, causing the unburned carbon particles to exit the exhaust system as black smoke.

In contrast, white smoke often suggests the presence of coolant in the combustion chamber due to a blown head gasket or a crack in the engine block. Blue smoke indicates that oil is being burned along with fuel, which can occur due to worn piston rings or valve seals. Clear smoke generally indicates normal operation or water vapor, which is not related to excessive fuel burning. Understanding these smoke colors is crucial for diagnosing engine issues effectively.