Diesel Engine Smoke: What Colour Means What?

Diesel Engine Smoke colour serves as a primary tool to understand and get to know the root cause of any ongoing problem with the engine.

Once you fall in love with the sheer power and torque offered by the diesel engines, there is no going back. Diesel engines are not only powerful and full of torque, but highly fuel efficient as well. However, a diesel engine has its own downsides and it is very important that these engines are maintained really well. A well-maintained diesel engine can go on for years, putting up huge miles on the odometer, without any major mechanical work.

One of the most prominent issues faced by the owners of the diesel vehicles is smoke. Yes, diesel engines smoke a lot and its not just limited to one kind of smoke.
Generally, smoke can be of three colours: black, white and blue. What smoke means what? Don’t worry, AutoHunters are here to help you understand diesel engine smoke.

  1. Black Smoke Black smoke indicates incomplete combustion of fuel and is a common site for diesel vehicle owners. A number of issues cause black smoke, such as:
    • Dirty or worn out fuel injectors.
    • Incorrect fuel injection timing.
    • Faulty turbocharger, or turbo lag
    • Faulty or dirty exhaust gas recycling (EGR) system
    • Incorrect valve clearance
    • Incorrect fuel to air ratio
    • Dirty or restricted air cleaner systems
    • Over loading the engine
    • Poor fuel quality
    • Cool operating temperatures
    • High altitude operation
    • Excessive carbon build-up in combustion and exhaust spaces

    While black smoke is most of the times, prominently visible under full power, or during the lag before the turbocharger boosts the air
    supply to match fuel usage, it can also be seen across the operating range of the engine. If some amount of black smoke is visible in the early stages of acceleration and during gear changes, you should not be worried, but if it is excessively high, you should get your car checked by a mechanic.

  2. Blue SmokeThe reason behind blue smoke is engine lubrication oil burning. The engine oil can enter the combustion chamber because of:
    • Worn valve guides, or seals
    • Cylinder &/or piston ring wear
    • Cylinder glaze
    • Piston ring sticking
    • Incorrect grade of oil .. too thin and getting past rings, or valves guides
    • Fuel dilution of the oil, making it too thin.

    During cold starts, blue smoke is most evident, which may reflect reduced oil control due to carbon fouling deposits around the piston rings and/or cylinder glaze. Blue smoke should not be evident at any stage. An engine may burn oil without blue smoke because modern engines have good compression which completely burns oil. You should regularly check engine oil levels and if the oil levels are found to be below than normal, even when you top up the oil to the maximum, then it is the time to go to the mechanic.

  3. White smoke White smoke is caused by raw and un-burnt fuel passing along with the exhaust gases. It can be caused due to:
    • Incorrect fuel injection timing: If the white smoke is constantly evident, it indicates a mechanical defect, or incorrect fuel timings.
    • Defective fuel injectors
    • Low cylinder compression: May be caused by leaking valves, sticking piston rings, ring wear, cylinder wear or cylinder glaze.

    When white smoke occurs at cold start and then disappears as the engine warms up, the most common causes are fouling deposits around piston rings and/or cylinder glazing. White smoke from the engine is any serious issue and you should take your car to the mechanic ASAP to save your car from any further damage.

    We hope that you found this article helpful.