What Does This Exhaust Color Mean?

The Indication Behind Blue, White, Gray or Black Smoke

CAR EXHAUST PUMPING OUT FUMES
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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 — some of which might not be normal or good. Things like burning oil, evaporating coolant and leaving unburned fuel in the exhaust 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 before they get worse and lead to expensive repairs.

Smoky Tailpipe Issues

Here, take a look at the most common symptoms and their causes to help you troubleshoot your exhaust by color and by smell. The symptoms below are the most commonly found smoky tailpipe conditions. 

  • Blue or gray smoke coming from the exhaust pipe.
  • White smoke or water vapor coming from the tailpipe, especially in the morning when the engine is cold.
  • Black smoke or very dark smoke coming from the exhaust pipe.
  • A new fuel odor or drop in MPG that seems to be coming from the exhaust pipe. 

Possible causes:

The engine's piston rings may be worn.
The Fix:
Replace piston rings. (This is generally not a DIY job)

The engine's valve seals may be worn.
The Fix:
Replace valve seals. (This is generally not a DIY job)

Damaged or worn valve guides.
The Fix:
Replace valve guides. (This is not a DIY job)

Burning Through Oil and Accompanying Smoke

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:

The PCV system is not working properly.
The Fix:
Replace PCV valve.

The engine may have mechanical problems.
The Fix:
Check compression to determine engine condition.

The engine's piston rings may be worn.
The Fix:
Replace piston rings. (This is generally not a DIY job)

The engine's valve seals may be worn.
The Fix:
Replace valve seals. (This is generally not a DIY job)

More Reasons Behind Abnormal Exhaust Smoke

Transmission fluid may be entering the intake manifold through vacuum modulator.
The Fix:
Replace vacuum modulator

Cylinder head gasket(s) may be bad.
The Fix:
Replace cylinder head gasket(s).

Cylinder head(s) may be warped or cracked.
The Fix:
Resurface or replace cylinder heads. (Resurfacing is not a DIY job)

The engine block may be cracked.
The Fix:
Replace engine block.

If you have a carburetor, the carburetor choke may be stuck closed.
The Fix:
Repair or replace choke.

Fuel injectors may be leaking.
The Fix:
Replace fuel injectors.

You may have a dirty air filter: Replace the air filter.

There may be some other type of ignition problem.
The Fix:
Check distributor cap and rotor. Ignition module may be bad.

If you have a carburetor, the carburetor choke may be stuck closed.
The Fix:
Repair or replace choke.

The engine may have mechanical problems.
The Fix:
Check compression to determine engine condition.

The ignition timing may be set wrong.
The Fix:
Adjust ignition timing.

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. (This is generally not a DIY job)

The engine may be running too hot.
The Fix:
Check and repair cooling system.

The fuel injectors may be stuck partially open.
The Fix:
Replace injectors.

There may be an emission-control device that is not working properly.

There may be some type of ignition problem.
The Fix:
Check and replace distributor cap, rotor, ignition wires, and spark plugs.

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. (This is generally not a DIY job)

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