What Causes Black Exhaust Smoke from Cars? (With Solutions)

How do I know what is causing black exhaust smoke from my car?

And how nervous must I be about black exhaust smoke? As I cruise down the highway with a plume of black smoke billowing from my exhaust.

Here are a few essential questions and solutions for the black exhaust smoke coming from your car.

Types of engine smoke

  • White Smoke: The engine might be burning coolant. The head gasket probably has a leak that allows coolant to drip through. It can also be caused by a damaged cylinder head or a cracked engine block.

This can cause overheating for your engine. There is also a chance the coolant might mix with the oil. Take your car in for a service as soon as you notice white exhaust smoke.

  • Black Smoke: This indicates your engine is using too much fuel. A clogged-up air filter can cause this. This will hamper the amount of air flowing through the filter.

The fuel pressure regulator can also be damaged. Or sensors and fuel injectors can be damaged.

If the fuel line is clogged up, it can also cause black smoke.

  • Blue Smoke: indicates the car is burning engine oil. When the piston rings wear out oil leaks into the combustion chamber. This means the oil is being burned with the fuel.

Turbocharged cars create blue exhaust smoke when the blower needs to be replaced.

The car won’t start smoothly as the oil can damage the spark plugs.

  • Grey Smoke: this can have two causes, one is that the car is burning oil. The other is that it has a bad turbocharger.

The automatic transmission fluid can be getting burned up in the engine. This means that the car has a faulty transmission modulator. This causes transmission fluid to get into the engine and be burned up.

What does black smoke from exhaust mean?

Black exhaust smoke means that your car’s engine is burning too much fuel.

If too much fuel is in the combustion chamber, it probably means there is not enough oxygen as well. Your car needs fuel and oxygen to burn at the same time. This lack of oxygen can cause black smoke.

Black smoke can be an indication there is something wrong with your car’s air filter, fuel injector, or EGR (for diesel).

These can all be fixed easily and inexpensively at your mechanic or service center.

Is black smoke from exhaust bad?

If you do not repair the cause of the black exhaust smoke, it can damage your engine.

This can lead to problems like; high fuel consumption, poor idling, and difficult starts. Stalling and misfiring can also happen.

Different scenarios of black exhaust smoke (with solutions)

a) What causes black smoke in a diesel engine?

Besides clogged filters and fuel injectors. Causes in a diesel engine are:

Bad Mass Air Flow (MAF) Sensor can be faulty when it thinks there is more air than fuel in the engine. This results in too much fuel being burned while the car indicates there is too much air.

Dirty Exhaust Gas Recirculation (EGR) Valve’s purpose is to re-circulate some of the engine exhaust back into the combustion chambers. This lowers the combustion temperature. This reduces the nitrogen oxides. If the amount is wrong, the EGR valve will stop working, and a build-up of nitrogen oxides takes place, causing black smoke.

b) What causes black smoke in a petrol engine?

A dirty air filter stops clean air from going into the engine. Dirty air will affect how the emission control systems work. This can lead to spark plugs wearing out.

Bad or faulty oxygen sensors can be the cause. If they are not sending the correct information to the engine control unit, this can cause your car to run inefficiently.

c) Black smoke from exhaust on startup

 Possible causes are a lack of oxygen to the engine or a faulty turbo. The engine is running on too much fuel.

Solutions can be to do the following if you have the necessary skills.

For a petrol car, you need to clean the air filters, replace oxygen sensors and replace or fix the auto computer (ECU).

For diesel cars, you need to clean the air filters and combustion system, check piston rings, invest in a common-rail fuel injection system, and use fuel detergent additives.

There may only be one of these causing a problem, so it is best to take your car to a mechanic or service center.

d) A black smoke when accelerating

 Possible causes area leaky fuel injector, faulty oxygen sensor or MAF sensor, too much fuel pressure. There can be a computer engine fault. It can also be caused by hard acceleration.

The fuel mixture can be too rich. There can be a stuck choke, a faulty fuel pump, or your carburetor might need to be adjusted.

The solution is to replace any faulty parts if you have the required knowledge. Otherwise, it is best to take your car to the mechanic or service center.

e) Black smoke from the exhaust when revving

A possible cause is most likely a dirty air filter. This is an indication the fuel is not being burned correctly. This can cause a solid carbon residue which then produces black smoke when revving your car.

Solutions are simply cleaning the air filter. If this does not solve the problem, then take your car to your mechanic or service center.

f) Black smoke on startup then disappears

A possible cause can be as simple as residual soot build-up in the exhaust pipe. Once it is burned away, then exhaust smoke will become clear. As stated above, if the smoke does not clear quickly, it can indicate a more serious problem.

Solutions can be to monitor the exhaust color and how quickly the black smoke is burned away. The longer the black exhaust smoke occurs, the more serious it can be. It is advised to take your car to the mechanic or service center.

If you have the required skills, you can replace the necessary parts.

g) Car shaking and smoking from hood

 A possible cause can be from oil or fluids that have been spilled onto the engine or exhaust system. It can be oil or fluids that are leaking onto a hot engine or the exhaust system.

Besides oil, the fluids can be engine coolant, power steering, brake, or transmission fluid. It can also be a window washing solvent.

The solutions are to pull the car over as soon as possible. Check if any warning lights have come on.

Check if there are any liquids dripping from the engine onto parts or onto the ground, then the car is no longer safe to drive. Do NOT touch the hot engine.

If you continue to drive, you can cause serious damage to the engine.

If you are not sure, then call a tow truck.

FAQ

  • Is it illegal to drive a car with black exhaust smoke?

If a car gives off smoke for more than 10 seconds, it is illegal to drive that car. You can be fined about $150 on the spot.

  • What color of exhaust smoke is bad?

The exhaust color must be light or a thin white. There will be some white, especially on a cold day.

  • Does black smoke mean running rich?

Yes, there is an imbalance of too much fuel and too little air.

Author: DJ

Dave Junior is a hands-on automotive technician with experience in performing service, diagnostics, and repairs on domestic and imported vehicles. He enjoys writing and sharing his knowledge far and wide.

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