An Informative Guide To Identify Causes For Strange Exhaust Colours

by IndianAuto Team | 03/12/2018
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On one fine day, you take your car out for a run. Suddenly you see a waft of visible smoke coming from your car’s exhaust pipe. Before freaking out and calling your trusty mechanics, do you know what the exhaust colour really means?

In a lot of cases, spotting a trail of vapour being emitted from the exhaust pipe is not an alarming thing, especially in wintertime. The exhaust pipe is where toxic and noxious gases are guided away from the engine, it is normal to have some smoke back there. Most of the smokes that you see coming out of the pipe on a daily basis have nothing to worry about. However, if you see the fume has a dark or grey tint, you may feel the need to contact your mechanics because that is an indicator that something is not working properly. A rule of thumb is that the longer the smoke keeps coming from the exhaust pipe and the darker its colour is, the faster you need to fix your car.


1. White exhaust smoke

Before feeling worried about your petrol car when you detect white exhaust smoke, you first need to see if it is actual smoke. It may sound silly, but in many situations, the light and thin white smoke that comes from the exhaust pipe can just be water vapour. If the “smoke” disappears quickly after you start your car, then you do not need to feel anxious about the chance of your car blowing up in the middle of your street. This happening occurs quite often, especially on cold days, and the “smoke” will naturally go away as the engine warms up.

Nonetheless, if the smoke is true smoke, which means that it is consistent, thick, heavy, and sometimes grey-tinted, your car is in trouble. The culprit could be cracked block, leaky head gasket, or cylinder head. No matter what the cause is, the car should be taken to the repair shop as soon as possible because these are serious problems and you probably do not want your car to break down on the side of the road.

petrol white smoke

Light white smoke means there is nothing wrong with your car, while thick white smoke indicates some serious troubles

2. Blue exhaust smoke

While there can be a few reasons as to why white smoke coming out of the exhaust pipe of a petrol-powered car, blue smoke in petrol car means only one thing: burning oil. That being said, the causes of burning oil are pretty plenty. The problem can lie in piston rings, valve seals, or cylinder walls. The damage in one of these part allows the oil to leak into the combustion chamber and burn with the fuel. If you do not take the car to repair quickly, your car will have some real issues with performance and the spark plugs can be ruined.

Note: You may notice that the blue smoke sometimes appears and sometimes disappears. If it streams out of the exhaust pipe when you accelerate, your piston rings are wrecked. In the case of deceleration, the valve seals are damaged. You may help your mechanics repair more quickly when you know these symptoms and notify them of the details.

petrol blue smoke

Burning oil causes the exhaust smoke to turn blue

3. Gray or black exhaust smoke

Even though the general rule is that the darker the smoke is, the faster the car should be checked out, you need not freak out when your beloved four-wheelers cough up some dark filthy black smoke. When your car does, the engine is probably burning too much fuel. The dark smoke can be attributed to a number of factors such as malfunctioning fuel injector, clogged air filter, and so on. In case you see black smoke, you should stop your car and check the air filter and intake components first, then you should examine the fuel return line to see whether it is clogged. A blocked air filter is a problem that is easier to tackle and poses little harm. If nothing is wrong with those parts, then call your mechanics immediately so they can figure out why your car is not burning fuel properly.

petrol black smoke

When a petrol-powered car emits black smoke, it is likely to burn more fuel than usual


Petrol and diesel engines are not very different from each other, but still, there are some dissimilarities. For example, a diesel-powered car does not have spark plugs, so if your diesel four-wheelers emit some nasty blue smoke, you do not have to worry about the spark plugs being damaged. Therefore, while their smokes can look similar in colours, the contributing factors can sometimes be different.

1. White exhaust smoke

Thin white smoke also occurs in diesel engines on cold days when you just start your car, and this kind of smoke is not anything to worry about; you can carry on with your day as usual.

In other cases that are more complicated, white smoke indicates that diesel is burned very little or not burned at all when going through the combustion chamber. A cold engine can be a cause to unburned diesel. Some more serious factors that may lead to this occurrence are:

  • Incorrect injection timing

  • Damaged injector

  • Leaky head gaskets

  • Cracked cylinder

  • Low cylinder compression

Most parts that may be involved in white smoke creation are pretty easy and inexpensive to repair, but if the problem lies in the head gaskets or the cracked cylinder, you should prepare your money.

diesel white smoke

White smoke coming from diesel car implies that little to no fuel is being burned

2. Blue exhaust smoke

When diesel car emits blue exhaust smoke, there is a high chance of oil burning just like how it goes with petrol cars. And the causes and details are pretty much the same as petrol engine.

When a diesel-powered car gives off blue smoke, it is quite the same story as a petrol-powered car

3. Gray or black exhaust smoke

Believe it or not, black smoke is actually the most common smoke that can flow out of the exhaust pipe of a diesel car. When you see your diesel car creates a black cloud behind, there is poor and incomplete combustion of the fuel. The cause of such happening is various, some of which are incorrect timing, overheating engine, overfueling, dirty or worn injectors, wrong grade of fuel, incorrect valve clearance, incorrect air/fuel ratio, and so on. Since there are so many elements that could potentially lead to the production of black smoke in diesel cars, it is recommended that you take your car to the mechanics so that they can take a look and decide on the best course of actions.

Black smoke is very common in diesel cars and can be generated by a multitude of factors

Read more tips and guides from IndianAuto

8 Common Reasons Why Your Engine is Overheating

5 Common Reasons Why Your Car Won’t Start & Troubleshooting Tips

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