Q:

Why does my car emit black exhaust smoke?

A:

Quick Answer

Black smoke from a car's exhaust is a sign that the engine is running too rich. The fuel is burning with incomplete combustion, and the black cloud includes the unburned carbon compounds. The NSW EPA says this is a sign the car is not properly maintained or poorly tuned. It is creating unnecessary air pollution and costing the driver more in fuel to operate.

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If the vehicle has a dirty air filter, it does not allow sufficient oxygen to reach the engine's cylinders for complete combustion. Replacing the air filter on most cars is a quick and inexpensive fix that increases fuel economy. The operator's manual includes a recommended replacement schedule.

In vehicles with a carburettor, the black smoke is often an indicator of flooding or a butterfly choke stuck in the closed position. These problems are often due to the carburettor needing service due to varnish that builds up from the fuel as it evaporates.

The color of the smoke from the exhaust gives important clues to problems with the vehicle. Once they reach normal operating temperature, gasoline vehicles should not produce smoke. When the vehicle is cold, white smoke is usually water vapor from condensation and not a reason for concern. Blue smoke from a vehicle indicates excessive wear and severe mechanical problems.

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Related Questions

  • Q:

    Why does white smoke come out of a car's exhaust?

    A:

    White smoke coming from a car's exhaust can stem from a variety of causes, the most common being condensation. Because of condensation, which occurs naturally as engines cool, water can become trapped in the exhaust pipes. Steam forms as the car heats up, escaping through the tail pipe.

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  • Q:

    Why does blue smoke come from my exhaust?

    A:

    Blue or gray smoke coming from an exhaust pipe indicates either an oil leak or piston wear. Typically, oil leaks pass the seals and get into the engine cylinder. From there, they come into contact with gasoline and burns, producing blue smoke. When oil leaks into the cylinder, it produces rough idle, misfires and could affect the spark plugs, according to CarsDirect.

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  • Q:

    Why does white smoke come from an exhaust pipe?

    A:

    White exhaust smoke is usually the result of condensation and moisture buildup in the exhaust system; it can also be the result of burning coolant within the engine. When white exhaust smoke is thin and vaporous, it usually does not signify a problem within the car.

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  • Q:

    Why does white smoke come from my exhaust pipe?

    A:

    Thin, white smoke coming from an exhaust pipe usually indicates normal condensation buildup in the exhaust, but thick, white smoke can indicate a problem like the engine burning coolant, a cracked engine block, a blown head gasket or damaged cylinder head. Thick, black smoke is generally a sign that the engine is burning excess fuel, and is typically not an indicator of as serious a problem as thick, white smoke.

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