Car exhaust smoke - Cheki Nigeria

Car Exhaust Smoke: Different Colours and What They Mean

Your car’s exhaust is easy to ignore because it is located at the back of your car. You probably only begin to worry when you notice smoke emission from your car’s exhaust.

You need to pay attention to all parts of your car and this includes your car’s exhaust. If you, however, notice your car exhaust emitting smoke, don’t let it unsettle you. This piece will educate you on what you need to look out for as well as what different colours of smoke from your car mean.

What to Look Out For When Your Car Exhaust Emits Smoke

The first thing you need to find out is whether the smoke from the exhaust is emitted when the car is stationary or when the car is in motion. These two situations are not the same and could have two different implications for your car.

Your next line of action should be to pay attention to the type of smoke that’s coming out of your car. Below are some of the things you should be on the lookout for:

  • Is the smoke white like clouds?
  • Is it grey and comes with a bit of a blue tinge to it?
  • Is it thick and black?
  • Does the smoke coming out evaporate as soon as it’s in the air
  • Rather than evaporate, does the smoke linger with a hint of an acrid smell?
  • If the smoke you’re seeing is black, does it leave soot on the road under the tip of the exhaust when the car is stationary?

What Could Cause Your Car to Emit Smoke?

The major cause of your car emitting smoke can vary but it rests squarely on the condition of the car. If your car is serviced on a regular basis and well maintained, then any emission or smoke should not give you sleepless nights. However, you will still need to have a look at it when you can.

You must understand that smoke from your car’s exhaust is first and foremost, a sign of neglect, which is why you should pay attention to it if you spot it during the inspection of a car you are plan to buy.

Below are highlights of the types of smokes you are likely to encounter as well as the implication they hold for the condition of your car.

White Smoke From the Exhaust

The white smoke from your car’s exhaust is the most common form of smoke but the truth is that it isn’t actually smoke. Here’s what happens – When the car’s engine is cold and you start the car, the engine begins to heat up and a byproduct of this is water vapour.

It triggers a condensation within the car’s exhaust system. This transforms into steam as the water vapour gets heated up by the rising temperatures in the engine and exhaust.

The moment the car’s engine is warmed up, this steam eventually evaporates completely. You are likely to encounter problems if your car constantly keeps covering short journeys, which prevents the exhaust system from getting completely warm all the way to the exhaust tip.

Blue Smoke From the Exhaust

If you come across blue smoke from your car’s exhaust, it will most likely be accompanied by a burning smell. What this means for your car is that you have a situation where oil is getting into the system somewhere.

The engine oil is expected to keep the moving parts lubricated and is not supposed to get into the fuel system if a car is running the way it was designed to run.

Other reasons you could have blue smoke from the exhaust could be:

If your car has been serviced recently – or you’ve serviced it yourself – it could be that too much oil has been put back into the system, and this excess oil is burning off. If the smoke stops after a while, then there’s no problem. Another cause could be that some oil has spilt onto the exhaust while being topped up, only to be heated and burnt off by the hot exhaust while you’re driving.

The piston rings or valve seals are worn (in a car with high mileage)

Oil is getting into the fuel system around the cylinders or valves because the piston rings or valve seals are worn

Your car is using more oil than it normally should

Solutions:

  • Get new seals all round. This could be expensive as the engine has to be taken apart to get to them
  • Ensure you check the dipstick regularly to find out how much oil loss is occurring. If it’s a minor oil loss, topping up the oil will fix this easier than a repair, as long as the oil loss doesn’t get worse.

Grey Smoke From the Exhaust

Just like the blue smoke, grey smoke tilts towards a problem of surplus oil-burning somewhere in the engine. In a turbocharged car, the turbo might need urgent attention.

Another cause of grey smoke could be traced to a faulty PCV valve. PCV stands for ‘Positive Crankcase Ventilation’ and it is one of the most basic forms of emission control for your car. It is designed to draw unburnt fuel back from the lower part of the engine back to the top.

If your car has an automatic gearbox and you see grey smoke, it could mean that transmission fluid is getting drawn into the engine through a leak in the system. Such a problem requires urgent repair and should be handled by a qualified mechanic or service centre.

Black Smoke From the Exhaust

First, you need to point out whether your car is powered by petrol or diesel. For cars that run on petrol, the black smoke from the exhaust can be traced to your car burning too much fuel

The solution to this is to start by checking the replacing your car’s air filter. This is usually found towards the front of your car’s engine bay in a black plastic case.

If the air filter is fine, you need to have a look at your car’s fuel injectors to see if they are clogged. You also need to ensure that the pressure regulator is clean. However, this task should be carried out by a qualified mechanic or a trusted car service centre.

For cars that run on diesel engines, black smoke can be caused by soot building up from unburnt diesel. The DPF, which stands for ‘Diesel Particulate Filter’ is designed to trap soot from unburnt diesel before it gets pumped out of the car’s exhaust.

You should, however, note that if your diesel engine car usually gets driven at low speeds, the soot deposit has a strong tendency to build up over a period of time. This could result in a warning light flashing on your car’s dashboard.

Solutions:

  • You need to get the fuel/air mixture going through the car faster, by driving the car faster. Find a free road like the Third Mainland Bridge on a weekend and accelerate your diesel car to about 112.6 km/hr. This should help you dislodge the soot, which will ideally appear in the form of a ball of black smoke behind the car. It should naturally leave soot deposits on the road as well.
  • For a used diesel car that pumps out black smoke frequently when you are driving it, you might need to get under the car to ensure the DPF is still part of the system. We have had cases of some rogue car sellers who remove the DPF from a problematic car to fix the issues but this will only cause the car to permanently pump out diesel soot. This will eventually transition into a potential MoT failure in the future.
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