What Does This Exhaust Color Mean?

Blue, White, Gray or Black Smoke From Your Tailpipe?

Exhaust Pipe Smoking
Don't tie it in a knot, find out why your car is smoking. Getty

If you've noticed that your car has thick smoke coming out of the exhaust pipe, it may be a sign that your engine needs some attention. Just like you can examine an animal's stool to get an idea of its health, you can pay attention to the quality of your car's exhaust to get an idea of what's going on inside the engine. As the engine burns fuel and creates exhaust, lots of different things are happening.

Unfortunately, some of these things aren't supposed to happen. Things like burning oil, evaporating coolant and leaving unburned fuel in the exhaust -- these are not good to see. Pay attention to what's coming out and you can get a good idea as to what problems your engine may be having, often before they get bad. This saves you money.

We've listed the most common symptoms and their causes to help you troubleshoot your exhaust by color and by smell. Follow the links to read up on what's happening in your engine. The symptoms below are the most commonly found smoky tailpipe conditions. 

  • My car has Blue or Gray Smoke coming from the exhaust pipe.
  • My car has White Smoke or Water Vapor coming from the tailpipe, especially in the morning when the engine is cold.
  • My car has Black Smoke or very dark smoke coming from the exhaust pipe.
  • My car has a new Fuel Odor or Drop in MPG that I think is coming from the exhaust pipe. 
    Symptom: Gray or blue smoke from the exhaust. You notice gray smoke coming from the exhaust when you start your car. The smoke may or may not disappear after the car is warmed. If it is, it is less noticeable. The smoke may have a bluish tint to it.

    Possible causes:

    1. The engine's piston rings may be worn.
      The Fix: Replace piston rings. (Generally not a DIY job)
    2. The engine's valve seals may be worn.
      The Fix: Replace valve seals. (Generally not a DIY job)
    1. Damaged or worn valve guides.
      The Fix: Replace valve guides. (Not a DIY job)

    Symptom: Engine uses more oil than normal, and there is some smoke from the exhaust. The oil level is low between oil changes. It appears that the oil is being burned by the engine because of the smoke in the exhaust. You may or may not notice the engine doesn't have the same power as it used to.

    Possible causes:

    1. The PCV system is not working properly.
      The Fix: Replace PCV valve.
    2. The engine may have mechanical problems.
      The Fix: Check compression to determine engine condition.
    3. The engine's piston rings may be worn.
      The Fix: Replace piston rings. (Generally not a DIY job)
    4. The engine's valve seals may be worn.
      The Fix: Replace valve seals. (Generally not a DIY job)
    Symptom: White smoke or water vapor from the exhaust. You notice white smoke coming from the exhaust when you start your car. If it is cold out, this may be normal. If the smoke does not disappear after the car is warmed, you have a problem.

    Possible causes:

    1. Transmission fluid may be entering the intake manifold through vacuum modulator.
      The Fix: Replace vacuum modulator
    2. Cylinder head gasket(s) may be bad.
      The Fix: Replace cylinder head gasket(s).
    1. Cylinder head(s) may be warped or cracked.
      The Fix: Resurface or replace cylinder heads. (Resurfacing is not a DIY job)
    2. The engine block may be cracked.
      The Fix: Replace engine block.
    Symptom: Black smoke from the exhaust. You notice black smoke coming from the exhaust when you start your car. The smoke may or may not disappear after the car is warmed. If it is, it is less noticeable. Engine may or may not be running rough or misfiring.

    Possible causes:

    1. If you have a carburetor, the carburetor choke may be stuck closed.
      The Fix: Repair or replace choke.
    2. Fuel injectors may be leaking.
      The Fix: Replace fuel injectors.
    1. You may have a dirty air filter: Replace the air filter.
    2. There may be some other type of ignition problem.
      The Fix: Check distributor cap and rotor. Ignition module may be bad.
    Symptom: The car uses more fuel than normal, and there is a strong odor from the exhaust. You notice that gas milage has gone down quite a bit. There is a strong smell like rotten eggs coming from the exhaust. You may or may not have noticed that the car doesn't have the same amount of power it used to.

    Possible causes:

    1. If you have a carburetor (seriously?), the carburetor choke may be stuck closed.
      The Fix: Repair or replace choke.
    1. The engine may have mechanical problems.
      The Fix: Check compression to determine engine condition.
    2. The ignition timing may be set wrong.
      The Fix: Adjust ignition timing.
    3. There may be a fault in the computerized engine control system:.
      The Fix:Check engine control systems with a scan tool. Test circuits and repair or replace components as required. (Generally not a DIY job)
    4. The engine may be running too hot.
      The Fix: Check and repair cooling system.
    5. The fuel injectors may be stuck partially open.
      The Fix: Replace injectors.
    6. There may be an emission-control device that is not working properly.
    7. There may be some type of ignition problem.
      The Fix: Check and replace distributor cap, rotor, ignition wires and spark plugs.
    8. The fuel pressure regulator may be operating at too high of a pressure.
      The Fix: Check fuel pressure with a fuel pressure gauge. Replace fuel pressure regulator. (Generally not a DIY job)