Which issue is most likely to cause blue exhaust smoke?

• A. Worn piston rings
• B. Restriction in the air inlet
• C. Coolant ingestion in a cylinder
• D. Cold operating temperatures

Answer: (A)

Blue exhaust smoke means oil is burning in the cylinder. When oil slips past worn piston rings, it enters the combustion chamber where it mixes with the air–fuel mixture and burns, producing blue-tinted exhaust. Worn piston rings are the classic cause because they no longer seal oil from entering the cylinder. The other scenarios don’t create blue smoke: a restriction in the air inlet changes airflow and tends to affect fuel mixture without burning oil; coolant entering the cylinder burns as white steam; cold operating temperatures mainly show condensation smoke, not oil burning. So worn piston rings best explain blue exhaust smoke.