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What causes black or white smoke to come from a diesel car’s exhaust?


Diesel engines are commonly associated with black smoke spewing from the exhaust, right?
You can often see, on uphill slopes and the like, trucks spitting out black smoke from behind.

I will tell you the reason why diesel engines produce black or white smoke.

Black smoke and white smoke are signals of a dangerous engine

Care must be taken when black smoke, white smoke, or both are emitted from the exhaust of a diesel engine.

Depending on the cause, this may be a sign of a malfunction or failure of the engine, so if you leave it as it is, in the worst case the engine may stop working.

What is the smoke?

The identity of black smoke

Caused by carbon buildup
Generally, the black smoke emitted by a diesel engine is soot produced at the time of combustion.

When some of the fuel injected into the cylinder evaporates before it burns, the carbon component remains, and it crystallizes. The carbon component mixes with the exhaust gas, so it comes out as a black smoke from the exhaust.

The color of parts of the car is black so that this carbon is not conspicuous.

The identity of white smoke

Caused by Engine oil
When engine oil burns for some reason, it may become white smoke and exit via the exhaust.

Caused by Water
As the engine runs, water vapor can become mixed with the exhaust gas, this steam may look like white smoke coming out of the exhaust.

What to do when you see black or white smoke

In the case of black smoke

The cause of black smoke is incomplete combustion. The main causes of incomplete combustion are as follows.

Cause 1: Insufficient air volume
Diesel engines constantly take a certain amount of air into the cylinder, and inject diesel there according to the depression of the accelerator.
However, if the amount of air is less than specified, all the diesel cannot be burned, causing incomplete combustion.

Corrective action
The shortage of air volume is caused by dirt clogging the air cleaner. Clean the air cleaner or replace it with a new one if the dirt is severe.

Cause 2: Fuel supply is defective
If the amount of fuel injected is too large, incomplete combustion will occur due to an excessively large proportion of fuel.
If the timing of fuel injection is bad, incomplete combustion will occur whether the timing is too advanced or too delayed.

Corrective action
Since there is a high possibility that malfunctions are occurring in the fuel injection system and the fuel pump, you should have them inspected and repaired by a mechanic.

Cause 3: Inadequate compression power
In diesel engines, the piston in the cylinder compresses air, and fuel is injected into the cylinder and spontaneously combusts. However, due to wear of the cylinder and piston ring, the required compression force is insufficient and incomplete combustion will occur.

Corrective action
Since it is caused by parts damage inside the engine, you will have to have the engine overhauled by a mechanic.
This is an expensive repair.

Cause of white smoke and its remedy

The causes of white smoke are engine oil or water vapour.
The main causes are as follows.

Cause 1: Oil rise
Oil rise is a phenomenon where engine oil rises from the oil pan at the bottom of the engine to the combustion chamber above it.
Because of wear of the piston ring which fills the gap between the piston and the cylinder, and scratches on the side of the cylinder, the engine oil enters the combustion chamber through the gap and burns together with the fuel.

Corrective action
Since piston rings and cylinders inside the engine are worn or damaged, if the engine is overhauled or cannot be repaired, the engine must be replaced and expensive repair expenses will be required.

Cause 2: Oil falling
Oil falling is a phenomenon in which engine oil drops from the stem seal filling the gap between the intake and exhaust valves in the upper part of the engine into the combustion chamber below the stem seal.

When the stem seal, which plays the role of filling the gap between the intake and exhaust valve, deteriorates or a gap is created due to expansion due to climate, engine oil enters the combustion chamber and burns together with the fuel.

Although replacing the stem seal with a new one will usually solve the problem, it is not a repair that a person not familiar with cars and engines can do. You should ask a professional mechanic to repair it.

Cause 3: Fuel is mixed with water
There are various causes for water contamination in fuel, for example, condensation in the fuel tank, fuel mixing, bad fuel originally mixed with water was put in, and so on.

Corrective action
One way to reduce air in the tank, which can help to prevent condensation from occurring, is by constantly filling up the fuel tank.
If water has been mixed in, basically, you should drain the fuel filter.
This is easy for anyone to do.

It seems that this will generally solve the problem, but in severe cases, it may be necessary to empty the fuel tank and drain the water.

Like the above, if abnormal smoke is seen coming out of your exhaust, you should ask a mechanic to inspect the vehicle immediately.

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