Why does my car emit smoke of different colours?

White, blue or black are some of the smoke colours that may indicate a fault in the engine.

Diesel cars produce much more smoke when they burn than petrol ones, so it is normal for them to generate some emissions. However, not all car smoke is the same, and some of it may be drawing the driver’s attention and indicating that the engine has a mechanical fault.

Depending on the colour of the smoke coming out of the exhaust, it will be a symptom of one fault or another. In this way, if you notice it, you can tackle the problem several months in advance and thus avoid possible bigger scares and larger bills at the workshop.

Why does the car emit thick white smoke on start-up?

If the car struggles to start and once it does, barely, it begins to expel a large amount of thick, whitish smoke, the fault stems from a lack of proper tuning of the diesel injection system. This is one of the most expensive failures a car can have and it can shorten the life of the engine.

It is important to know that this whitish smoke is actually diesel vapour. It may be caused by the injection pump being out of timing, injecting the fuel too early or too late.

Another reason why your car gives off white smoke on start-up is that a heater, or glow plug in vehicles with Common Rail systems, is in poor condition.

Why does the car emit white smoke when it is warm?

There is no need to panic too much, because if the smoke is not very dense, it may be produced by water vapour present in the exhaust. This happens because burning fuel generates water vapour, which condenses as it cools and stays in the exhaust.

For this reason, when the engine starts to warm up it begins to evaporate and exit. If the driver notices that these emissions persist over time, it is very likely a fault in the cooling system.

It is important to know that this type of fault has a very distinctive smell and is usually accompanied by a rise in temperature and pressure in the cooling circuit. If it is not repaired in time, it can cause the cylinder head gasket to deteriorate.

Why does the car emit blue smoke?

If, while driving, the vehicle is seen giving off a bluish smoke with a peculiar smell, the fault is that oil is mixing into the combustion chamber.

This may be due to a deteriorated cylinder head gasket, a worn turbocharger, worn valve stem seals, or piston rings that have begun to deteriorate and lead to engine fatigue.

Why does the car emit black smoke when accelerating?

First of all, it is important to know that the car generates black smoke when diesel does not burn properly. It may be caused by a lack of oxygen or poor injection.

It is common to say that older diesel cars are “smoky clunkers”, and indeed many of them have this fault, which can be endemic. If it emits black smoke when accelerating at that moment, it is normal. What would be worrying is if it kept expelling smoke of this colour for some time.

In addition to a possible injection fault, it may be due to a deteriorated EGR valve, an air leak in the intake manifold, or even a faulty mass air flow sensor.