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What Does Black Smoke from Exhaust Mean - All Possible Reasons

 
By Nidhi Nangia. Updated: July 25, 2017
What Does Black Smoke from Exhaust Mean - All Possible Reasons

As an engine starts to wear out and age, it begins to change as well. It may still work fine, but it isn’t as powerful and efficient as it was when it was new. Many old engines become hot and seep out excess emissions from their exhaust pipe. Initially, you may not notice these emissions, but as time passes and you leave them unattended, they begin to emanate as smoke from your exhaust. Smoke coming out from your exhaust may be of different colors, and each color may mean different issues. Smoke from your exhaust can be white, blue, black or gray. In this oneHOWTO article, we will talk about what does black smoke from exhaust mean.

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Black Smoke from a Diesel car exhaust

If your vehicle runs on diesel, then over-fueling may be the primary cause of black smoke coming out of your exhaust pipe. When the fuel injector of a heavy duty diesel engine wears out, it causes the nozzle hole to enlarge or the injector needle to erode. This allows excess fuel to enter into the engine’s combustion chamber. Many times, the needle and nozzle wear down due to corrosion from high sulfur or contaminated diesel fuel. A diesel engine is not designed to burn excess fuel. Due to this, fuel is wasted and it exits from the exhaust while it is not combusted completely. This partially combusted fuel coming out of the exhaust pipe appears as black smoke.

In this case, it's best you take your car to a professional mechanic so he/she can change your fuel injector and stop your car from emitting this black smoke. To avoid this from happening, make sure you clean your fuel injector.

Black smoke when accelerating

If you see black smoke coming out of your exhaust when you accelerate it hard or when it is heavily loaded, then it may indicate incomplete combustion of the diesel fuel in it, along with a few traces of the engine lubricant. The exhaust usually contains soot (elemental carbon), sulfates (mainly sulfuric acid), water vapor, and semi-volatile organic hydro-carbons. Elemental carbon is black and is made when fuel in the car’s combustion cylinder does not get combusted completely. Incomplete combustion leads to the formation of soot, especially when there is excess of lube oil and diesel fuel. It is also caused when it stays in the combustion zone for a shorter period of time, and when there is lack of sufficient oxidants.

In order to remove the soot from the car, you can try removing it with a paint cleaner, although, if it is too far inside, you will have to take it to a professional to have it cleaned and fixed.

What Does Black Smoke from Exhaust Mean - All Possible Reasons - Black smoke when accelerating

Other Causes Of Black Smoke From Exhaust

There are other reasons why black smoke comes from your car exhaust, take a look at other symptoms to identify your problem.

Dirty Air Filters

Dirty air filters do not allow oxidants to enter into your engine’s combustion chamber, due to which the fuel does not get combusted completely and this ultimately leads to black smoke coming out of your exhaust pipe. According to an estimate, dirty air filters can increase particulate matter coming out of your car’s exhaust system by as much as 50%.

Excessive consumption of oil

Worn out valves, valve stem seals, cylinder liners and deposit rings may lead to excessive oil consumption, due to which black smoke may come out of your exhaust pipe.

Engine wear

Black smoke from exhaust can result from excessive intervals between oil drains, contaminated oil, wrong oil for application, improper maintenance of proper levels of oil in the engine etc. Ensuring regular maintenance with the right lubricant will minimize deposits and wear to prevent black smoke. At oneHOWTO we recommend you take a look at our article on how to maintain a turbo diesel engine.

Poorly maintained oil levels

If you are seeing black smoke from your exhaust, then probably you are not maintaining the right oil levels in your engine. If you keep them at optimum levels, your engine will steadily consume the oil in your car as it drives, which means that engine is consuming all the oil you have entered in it. But if black smoke is coming, then it may mean that some oil is left behind unburnt, and it is being forced out from the exhaust pipe in the form of black smoke.

Clogged catalyst

Another of the reasons of black smoke coming from your exhaust is because you have a clogged catalyst. You will identify this problem because you will also hear a rattling noise and will notice a distinct "rotten egg" smell. This may also cause a carbon buildup as mentioned before, but at a more advanced stage.

What to do

Regular maintenance of your vehicle and use of right oil can prevent pre-mature wear of your engine that contributes to emission of black smoke from your exhaust. Clean your fuel injector nozzles regularly, and replace them when needed. Check and clean or replace your air filters whenever required. Change and top up your oil consistently and use recommended oil only to prevent excessive wear to your ring, train and cylinder.

If you want to read similar articles to What Does Black Smoke from Exhaust Mean - All Possible Reasons, we recommend you visit our Car Maintenance and Repair category.

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