6 reasons for white, blue & black exhaust smoke: Diesel, accelerating, startup

What does white smoke coming from the exhaust mean?

It is normal for a new diesel engine to experience blow-by upon startup, especially if it is running at full load. It is a condition where the fuel and air are pushed into the crankcase of the engine. You should ensure that the correct pressure is always maintained in the cylinder chamber. It will allow for ideal combustion and good performance. 

If the diesel engine is working properly, it should not produce any kind of smoke. If you notice smoke coming from the exhaust, you should investigate the engine since this is a warning sign. You will experience three different colors of diesel engine smoke. It can be either white, black, or blue, and they are all indications of a problem with the engine. 

In older models, light white smoke can come out during quick acceleration, which is acceptable. It happens because there is a lag before the airflow can match the increased fuel volume. For new models, this problem is solved through rail injectors that easily match the turbocharger’s speed.

If you notice smoke coming from your vehicle’s exhaust, continue reading as we talk about 6 reasons for white, blue, and black exhaust smoke. Whether it happens with diesel engines during startup or while accelerating, we will explore each situation in detail. 

What causes white smoke from the exhaust of a diesel car?

There are many causes for white smoke coming out of the exhaust. They often occur in cars with a diesel engine. Let’s take a look at the 6 most common reasons.

1. Transmission fluid leak

transmission fluid

The transmission fluid causes white smoke if this liquid is leaking out of your vehicle. This liquid will generate white smoke when burnt, but a broken diaphragm valve might cause a leak of the transmission fluid. 

Cracked transmission gaskets can also cause leaks as they are exposed to high temperatures. Suppose you notice excessive smoke coming out of the exhaust. In that case, you should take your vehicle to an auto repair shop as soon as possible. 

A skilled mechanic can diagnose and locate the cause of the problem. Once they identify the leak, they can also fix it. However, you will need to replace some transmission parts if they are completely damaged and causing leaks. 

2. Leaking valve seals or piston rings

If the piston rings are damaged and worn, they can cause leaks of oil into the combustion chamber. Once this oil is mixed with the fuel, it will cause problems and lots of white smoke from the exhaust. Your engine will also lose power because it lacks compression.

Most likely, an expert mechanic will perform a pressure test on the engine. They are ready for such problems and know how to solve them easily. This test will determine whether a valve stem or a piston causes the leak and loss of performance. 

If the cause has been identified, the top part of your engine will be completely dismantled to replace the broken part. Labor costs can significantly increase for such an operation. 

3. Clogged fuel filter

fuel filter for a car

If the above causes do not apply to you, consider the fuel filter a possible problem. If this filter is clogged or damaged, it can result in a lot of white smoke coming out of the exhaust. 

It is well known that diesel fuel filters will get clogged over time, but water and rust can speed up this process. Eventually, an unbalanced mix of fuel and air in the combustion chamber will create other problems. It happens because the filter restricts the flow due to contaminants and debris. 

In some cases, the fuel will pass completely unfiltered. It causes water to mix with the fuel in the combustion chamber. You know this problem applies to you when you notice gray or white smoke that smells like raw fuel. 

4. Coolant leak

BMW coolant

If your engine is also overheating, the problem might be caused by a coolant leak. If there is a leak in the engine block, the coolant can pass through cracks and gaps. It will mix up with the diesel in the combustion chamber and turn into a thick white smoke once ignited. A specific smell will help you identify if a coolant leak causes your problem.

If this is true for you, you will have to open the hood and inspect the engine compartment. There should be green residue visible from the dried coolant. While under the hood, check the coolant level and notice if it is lower than usual. 

At this point, it is dangerous to start the engine because you might cause further damage to its components. Your most important priority is now fixing the leaks and gaps to prevent additional leaks. 

5. Condensation

Whether you drive a BMW or ride a motorcycle, it is normal for a bit of white smoke to appear after you start the engine. White smoke is almost guaranteed if you leave your vehicle in the garage over the weekend. 

It is caused by the condensation inside the exhaust pipes and catalytic converter. This condensation evaporates and mixes with the exhaust gas as the engine begins to heat up. The result is a thin white smoke that might even continue while driving. 

However, it should disappear once the engine has been turned on for a while and has had enough time to warm up fully. But if it persists or it gains a bluish color, it can be a sign of a more serious problem. 

6. Broken injection timing

The last common cause of white smoke from the exhaust is a broken injection timing. It often occurs in diesel engines, whose fuel injectors are very sensitive to external factors. Contaminants like rust or debris can easily clog the spray tip and prevent the injector from fully closing.

As a result, the pattern and timing of the injector will create an inadequate mix of fuel and air during combustion. Therefore, thick white smoke will be generated as raw fuel passes through the exhaust. 

You can easily identify this problem if you also experience sputtering or other engine problems. In this case, an inspection is mandatory. You should have an expert look at your vehicle as soon as possible. 

White smoke from the exhaust when accelerating or revving

Suppose your vehicle produces white smoke when you hit the gas and accelerate. In that case, it can indicate something is wrong with the engine. Sometimes, it can be a simple issue that only requires minimal repairs. 

But this can also happen due to more serious problems where the engine will need serious repairs. Suppose you notice white smoke when you accelerate. In that case, you should ask towing services for help. Driving a vehicle with a broken engine is not recommended. 

Suppose the problem is related to gasket failures or a crack in the engine. Your car will experience overheating as well as contamination. It could lead to additional problems, and your repair costs will significantly increase. 

White smoke from exhaust on startup then goes away.

transmission fluid, big container

Sometimes you will notice white smoke coming out of the exhaust when you start your engine. As you begin to worry about the problem, it quickly goes away, and you can drive without any problem. While it looks like the problem fixed itself, you should not neglect it as it represents an issue with your car. 

But there are some cases where the smoke is simply a result of the exhaust pipe collecting steam after the ignition. There are many reasons why you might experience this, and some of the serious problems you should consider are:

  • Low transmission fluid
  • Wrong pump timing injection
  • Dirty air filter
  • Coolant leak
  • Valve seal or piston ring leak
  • Internal engine issues

Additionally, you should also consider water being present in the exhaust pipe. If you notice water coming out of the exhaust, seek the help of a mechanic. They will help you fix this problem as soon as possible. 

Blue smoke from the exhaust

While white smoke is quite common, you will experience blue smoke less often. It is the rarest type that can come from a diesel car’s exhaust. When this happens, the blue color is a result of burning oil. It is a problem that should not be ignored but is quite common when starting the engine in cold weather.

As the oil thins out when temperatures drop, some of it can escape into the cylinder and be burnt during ignition. Other common causes of blue smoke should also be considered, such as: 

  • Wrong grade of oil
  • Fuel mixed with oil
  • Damaged guides
  • Damaged cylinders
  • The engine is overfilled with oil

Black smoke from the exhaust

intercooler

Unlike white smoke, you will find out that black smoke has a high concentration of carbon. It indicates that there is something wrong with the combustion process of the fuel. 

When diagnosing the problem, look at the mixture of air and fuel that flow into the cylinder. This mixture has to be balanced. Otherwise, bad smoke will come out of the exhaust.

But there are many more causes of black smoke, and some of them include:

  • Damaged injectors
  • Damaged intercooler
  • Improper valve clearance
  • Over fueling
  • Clogged fuel filter
  • Clogged air filter
  • Damaged turbocharger
turbocharger

Gray smoke from the exhaust

Gray smoke usually means that there is oil burning inside the combustion chamber. It happens because of a leak or a crack. Sometimes, the smoke can also be blue. While this won’t cause extensive damage to your engine, it can be a good sign that it is at the end of its lifespan.

Your oil levels are also being depleted, and you will have to fill the engine with oil more often. If you don’t do it regularly, it could cause massive engine damage that sometimes is irreversible. 

How to fix white smoke from the exhaust

The method of fixing white smoke from the exhaust depends on the problem and its cause. If coolant is getting into the combustion chamber, it mostly happens due to leaks or cracks. In this case, you will have to replace the head gasket and repair any additional leaks before they completely damage your engine.

Some problems will fix themselves, such as in situations where white smoke results from condensation in the tailpipe. All you have to do is be patient, and it will disappear as you drive. 

But some issues could be more serious. If the cylinder head is cracked, you will need to replace it. This operation takes a lot of time. The cost of parts can take up to $1,000 from your wallet

FAQ

Can too much oil cause white smoke from exhaust?

Oil pans installed in cars are designed in such a way that they can hold a specific volume of liquid. The fluid heat expansion and pressure of the oil on components are also considered, so there will always be an ideal amount of oil in the pan.

But when you overfill it, you will experience white smoke. Excess oil will burn within the engine block, and you will see dense white smoke in the rearview mirror as you drive. Additionally, you might also experience oil leaks which will cause more problems.

Check your vehicle’s owner manual and identify the ideal amount of oil. Do not exceed this limit. Never overfill your car’s oil pan. This way, you will avoid several problems in the future. 

Is white smoke from exhaust bad?

White smoke usually means a high danger level and should not be ignored. Unless the smoke is generated by condensation, which is quite normal, you should always take this symptom seriously. 

Coolant might be burning in the engine, or the head gasket is blown. Your engine will start overheating, and this leads to many more problems. If a cracked cylinder or engine block causes the smoke, you might have to replace the entire component completely.

When you notice it coming out of the exhaust, check in with a mechanic and ask for professional help. Whether the problem is serious or not, prevention is important.

Why do diesel cars blow black smoke?

Gasoline engines are less likely to produce a black substance formed by the combustion process. Diesel ones will produce it more often because they need compression in order to achieve an ideal pressure and temperature. 

When there is reduced compression, the mixture will not burn instantly. As a result, large amounts of black smoke could come out of the exhaust. 

Can a leaky injector cause blue smoke?

While blue smoke is often associated with oil leakage, there could be many more reasons your vehicle lets out the smoke with a bluish hue. Worn piston rings can result in this symptom, meaning you will have to replace these parts. 

But more and more drivers are reporting issues related to worn and leaky injectors. If this is your case, fixing them becomes your top priority. The health of your engine is at risk and you should not operate your vehicle until you get it fixed. 

Regardless of the color, if there is something wrong with the engine, you should always contact the local auto repair shop. The staff there will be happy to assist you with the problem.