White Smoke From Exhaust During Startup, Revving or Acceleration: Possible Causes

A thick or light white smoke from the exhaust on startup and while accelerating and revving can be a problem with the engine. As a driver, you must be aware of the smoke coming out of your vehicle’s exhaust pipe. Not only does it damage the environment but it is harmful to your health too. It is well-known that the white smoke coming out of your exhaust system is harmful to your health. It is known as a carcinogen and can cause serious health issues. Keeping in view this serious issue, I have figured out some important causes of white smoke from the exhaust of vehicles. So, let’s dive in and explore those causes.

White smoke from a vehicle’s exhaust commonly results from condensation in the tailpipe, particularly in cold conditions or at startup. This thin smoke typically disappears quickly and can occur if the vehicle is not driven often. However, continuous, thick white smoke could indicate a more serious issue, such as a coolant leak into the engine cylinder through a blown head gasket, leading to overheating. It is advised to monitor the coolant level and engine temperature in such cases.

Is your vehicle facing a low oil pressure issue? Check out my guide on low oil pressure at idle.

What Are Exhaust Emissions? 

The exhaust emissions are the gases emitted from the tailpipe of an internal combustion engine. They are the byproducts of the burning of gasoline or diesel fuel. Exhaust emissions are passed through a catalytic converter to reduce harmful emissions and through the muffler in the exhaust system of a vehicle to reduce noise. 

Exhaust emissions are classified as primary and secondary pollutants. Carbon monoxide, nitrogen oxides (NOx), and hydrocarbons are primary pollutants. Carbon monoxide is a colorless gas that is toxic.

Nitrogen oxides are also colorless gas that is toxic. Hydrocarbons are a group of organic compounds that include various volatile substances. These chemicals are usually formed when incomplete combustion occurs.

The secondary pollutants are particulate matter and sulfur dioxide. Particulate matter is the solid particles of soot or dust that are formed in the combustion process. Sulfur dioxide is a colorless gas that is also toxic. It is produced when sulfur in fuel combines with oxygen in the air.

What Do Exhaust Emissions Normally Look Like? 

If everything is fine in the engine, emissions are usually colorless. If just on the startup of your vehicle, you see a puff of a thin white smoke from the tailpipe, it is just steam that is converted from the water built up in the exhaust system due to the condensation.

That thin white smoke from the tailpipe only lasts for a minute after the engine startup. So, you don’t have to worry about it. However, if it’s thick white smoke, your car may have a problem. Neglecting that smoke could put your engine at serious risk of damage.

Car won’t start after getting guide? Take help from here.

Is White Smoke From A Car Exhaust Normal In Cold Weather?

In cold weather, the majority of white smoke emissions are normal. It usually indicates condensation, which is the result of water vapor in the exhaust mixing with colder air. This produces a mist that resembles white smoke.

That said, white smoke can also signal issues with the car’s engine. If you’re seeing a large amount of white smoke coming from your car’s exhaust, it could mean that the engine is burning coolant, which is a sign of a head gasket failure. This happens when coolant enters the combustion chamber and burns, creating white smoke.

Causes Of White Smoke From Exhaust

Here are the causes of white smoke from the exhaust.

1. Too Much Oil in the Engine

White smoke from the exhaust on startup after an oil change can occur if you put too much oil into the engine. It is possible that enough fresh oil leaks down past the valve guides as it is poured through the rocker covers. When excess oil is poured into the engine, it bypasses the piston rings and valve seals, due to which it is burnt in the combustion system. If that is the case, all you need to do is first check the oil level using the dipstick.

In the owner’s manual, it is mentioned to check the optimum oil level using the dipstick. Usually, there are two marks on a dipstick. The oil level should be between those two marks on the dipstick. If there is excess oil,  all have to do is pull the drain plug and drain a couple of quarts, or vacuum a couple of quarts out.

Here is what says a person in a forum about his experience of white smoke from the exhaust when there was too much oil in a car.

“Happened to me with the Honda. Did some 2500km road trip and then chucked in about 1.5 liters for good measure without even having a look with the stick. – Silly me. The next morning, the moment I joined the autobahn and went over 4000 revs I laid down a white smoke screen. Went into the next rest area, and called the TCS (Swiss assistance), guy came, and gave the poor Honda some more revs, resulting in another gigantic artificial white cloud. Then he went under the car and drained some oil. And then drained some more. Took out at least 2 liters. – Car was fine again after two more minutes.”

2. Valve Stem Seal or Piston Ring Is Damaged

If the white smoke from the exhaust has a nasty smell, it means that oil is burning in the engine. Now, first, you need to follow the above steps to see whether your engine is overfilled with the motor oil.

If after removing the excess oil, there is still a bellow of white smoke, the valve stem seal or piston ring may be damaged. If the valve steam seal or piston ring is broken, the oil may enter the combustion area and burn with the fuel. As a result, you might see a bluish tint in the thick white smoke from the exhaust tailpipe.

3. Coolant is Leaking Internally

Normally, if a thick white smoke is continuously coming out of the tailpipe when driving, this can be a sign of a coolant leaking internally. As you drive a car, and the white smoke comes out of the exhaust but fades over time, the tiny leaking gaps in the engine are filled by the expanding metal of the engine as it starts warming up.

To diagnose whether the coolant is leaking in the engine, try to smell the smoke. If it’s is a slight sweet smell like maple syrup, it means that coolant (antifreeze) is leaking through a blown head gasket, cracked cylinder head, or a crack somewhere in the engine block, and burning off in the engine cylinder. A Head gasket is present between the cylinder head and engine block. The cylinder head has compartments to place the valve stem.

Moreover, if you open the oil cap, you will see a chocolate milk residue on the cap. Also, check if there is any oil in the radiator by opening the radiator cap. Furthermore, if the coolant level is too low in the radiator, there is no doubt that the coolant leakage is the cause of white smoke from the tailpipe of your vehicle.

To diagnose the head gasket leakage, you have to perform a compression test. You can check out the below to perform a compression test for the head gasket.

Get a compression test kit from here.

4. Leaking of Transmission Fluid

If there is white or light grey smoke from the exhaust tailpipe while you are accelerating or reversing your car, you are also feeling a slight jerk with the transmission, and if the check engine light is on, the chances are that the transmission fluid is getting into the engine. The transmission fluid leaking problem most probably occurs in the older cars having vacuum modulators.

The transmission fluid gets into the engine when it is pulled through the vacuum hose if the vacuum modulator of the auto-transmission system is faulty. That vacuum hose runs from the modulator on the transmission to the engine’s intake manifold. If the vacuum modulator valve is faulty, transmission fluid will leak through it and will be sucked up the vacuum line to the intake manifold of the engine.

To test the vacuum modulator, you can perform the following steps:

• Shift the transmission to park mode and set the emergency brake.
• Warm up the engine to the normal temperature.
• Watch the exhaust and see if there’s any smoke coming out of it.
• If there’s white smoke, then the diaphragm of the valve is leaking and drawing up the transmission fluid into the engine.

5. Clogged Fuel Filter

If you have a diesel engine, a clogged fuel filter can be the cause of white smoke from the exhaust. The color of the exhaust will most probably be whitish-grey in a diesel engine. Diesel smoke has a different color from gasoline smoke. If the problem is related to the fuel delivery system, then there will be black smoke from the exhaust in the gasoline engines.

Since this article is related to the white smoke from the exhaust, I’m assuming that you have a diesel engine and your fuel filter is clogged which is not delivering sufficient fuel to the fuel injectors. Fuel filters are clogged due to contaminants in the diesel fuel that start building up on the fuel filters over time. 

Now, due to a clogged fuel filter, here is what happens with the diesel:

• Diesel enters the engine cylinder unfiltered. As a result, it contains several contaminants
• Sufficient diesel fuel cannot enter the engine cylinder as the fuel filter is clogged.

Due to the above reasons, insufficient combustion takes place. As a result, there is a low combustion temperature, which causes whitish-grey smoke from the exhaust in diesel engines. This whitish color is because of the raw fuel in the exhaust gases.

6. Faulty Fuel Injector

Fuel injectors failure is one of the major causes of white smoke from the exhaust in diesel engines. 

It may be due to several reasons such as the failure of the fuel pump or the failure of the fuel injection system. 

Fuel injection systems consist of several components such as the high-pressure fuel pump, the control unit, the injector body, the inlet and outlet piping, the nozzle body, the high-pressure spring, the relief valve, the filter, the pressure regulator, and the air filter.

All these components must be installed correctly to ensure proper fuel injection. When any of these components fail, the fuel injector that delivers the fuel to the combustion chamber can leak or become stuck in the open position. This means too much fuel in the engine that needs to burn off and be expelled. This is seen as gray or white smoke from the exhaust from the tailpipe.

To replace fuel injectors, you can check out the below video:

7. Cracked Engine Block

Engine block is the part of the car’s engine that holds the pistons, connecting rods, and other parts. It is made of cast iron or aluminum. It is also the component of the engine that absorbs the vibration of the engine. Engine block also has passages for coolant and galleries for oil.

It is the first thing that an engine builder checks while building a new engine. The engine block is often the most expensive part of the engine because it requires special tools to manufacture and must be machined.

If any of the engine components are not properly working, the overheating can produce cracks in the engine block. As a result, the oil and coolant can leak into the engine cylinders where combustion takes place. Due to the burning of coolant and motor oil, white smoke comes out of the exhaust.

Depending on your vehicle, the cost of a new engine block ranges from $600 to $2500. So, before replacing the engine block, go to the mechanic and perform the test to verify whether there is a crack in the engine block or not.

Final Thoughts

So, if a thin white smoke is coming out of your car exhaust, it can be due to:

• Cold weather that causes condensation in the exhaust system
• Starting a car after a long time. Moisture builds up in the engine.

A cloud of thick white smoke from the exhaust is due to:

• Faulty fuel injector
• Coolant leakage through the engine head, head-gasket, or engine block
• Too much oil is present in the engine
• Oil is leaking through the valve stem or piston rings

White Smoke From Exhaust On Startup Then Goes Away

One possible cause is condensation buildup in the exhaust system. When your car is turned off, moisture can accumulate in the exhaust pipes. As your engine starts and heats up, this moisture evaporates, resulting in white smoke. This is often a normal occurrence, especially in colder weather conditions.