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What Does the
Color of My
Exhaust Smoke
Mean?

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Modern vehicles should only produce thin white smoke upon startup or no visible smoke at all during normal operation. If your vehicle is emitting a significant amount of smoke from the exhaust, then it might have some issues. Your vehicle can emit different colors of smoke, with four most common colors that indicate an issue. Changes in smoke color are usually caused by nearby fluids entering the combustion chamber. Knowing the color of your vehicle’s exhaust gases can be a good indicator of a problem’s severity because the smoke’s color can give you an idea of which part is broken. In this article, we’ll discuss the different smoke colors that can be emitted by your vehicle’s exhaust as well as their potential causes.

white smoke
different smoke

What Kind of Smoke Is Normal?

Vehicle engines are equipped with several sensors that help the powertrain control module (PCM) determine the correct air-fuel ratio and ignition timing, which allows the engine to run efficiently. As a result, vehicles without any issues should emit very little smoke.

If you see thin white smoke from your exhaust, don't be alarmed. This type of smoke is water condensation or tiny water droplets that look like steam. Vehicles typically release thin white smoke after a cold start because exhaust gases can still cool as they pass through the cold tailpipe and result in more condensation. If you live somewhere cold, then your vehicle may regularly emit this type of smoke.

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That Signify a Problem

01 Persistent Milky White Smoke

Thicker white smoke is typically caused by coolant getting into the combustion chamber. If you suspect that this is happening, check your vehicle's coolant levels to see if it’s decreased. If coolant is burning, your vehicle's exhaust might also have a sweet smell. This can be caused by several possible issues:

keyboard_arrow_right Cracked block or cylinder head

The engine block or cylinder head can crack and cause oil and coolant to seep into the combustion chamber. Unlike the head gasket, you can't simply repair the engine block and cylinder head. You'll most likely end up replacing either of these parts because repairing them is labor-intensive and more expensive, as they're usually made from a single piece of cast iron or aluminum alloy.

keyboard_arrow_right A blown head gasket

The head gasket is responsible for sealing the gap between the cylinder head and the engine block. It's also responsible for keeping the oil and coolant channels apart. If the head gasket cracks, it will cause oil and coolant to mix and seep into the combustion chamber.

Coolant and oil should never mix in your engine. Coolant doesn't have the lubricating properties of engine oil, so when the oil and coolant mix it will cause parts to wear much faster. If your vehicle starts to emit a lot of white smoke, you should stop immediately because keeping the engine on can damage components like valves and pistons. It can also cause your engine to overheat, which can result in more damage.

02 Blue or Gray Smoke

Blue smoke coming from your vehicle’s exhaust likely means that your engine is burning oil alongside regular fuel. You're also likely to notice that the blue smoke has a strong burning smell. Several components around the combustion chamber can wear out after years of use and result in oil leaking into the combustion chamber. These include the following parts:

keyboard_arrow_right Damaged piston rings

Piston rings are responsible for isolating the pressure inside the combustion chamber.

keyboard_arrow_right Worn cylinder walls

Like piston rings, the engine block’s cylinder walls are also responsible for isolating pressure inside the combustion chamber. However, unlike the piston rings, worn-out cylinder walls can’t simply be replaced because they’re part of the engine block.

keyboard_arrow_right Faulty turbocharger

Turbochargers also need oil for lubrication. When they wear out, oil can also leak and enter the combustion chamber.

keyboard_arrow_right Faulty valve stem seals

Valve stem seals prevent oil from entering the combustion chamber through the gap between the valve stem and guide. A worn valve stem seal can fail to prevent oil from seeping into the combustion chamber.

keyboard_arrow_right Bad positive crankcase ventilation valve

The positive crankcase ventilation (PCV) valve lets out exhaust gases that manage to get past the piston rings and enter the crankcase. A stuck PCV valve can cause oil to be pulled from the crankcase and burned inside of the engine.

If your vehicle is emitting blue or gray smoke, have it checked by a mechanic immediately. While oil mixing into the combustion chamber might not sound alarming, this is essentially an oil leak and you should treat it with the same level of urgency. If left unrepaired, your engine might end up running low on oil, which can cause other problems like overheating and excessive engine wear.

03 Thick Black Smoke

If your vehicle is creating too much black smoke from the exhaust, then your vehicle is probably burning too much fuel. There are several components that can cause your engine to inject too much fuel into the combustion chamber:

keyboard_arrow_right Clogged fuel injector

Fuel injectors open and close at a very specific interval. However, they can get clogged by carbon residue. When this happens, they can remain open for an extended period and inject excessive amounts of fuel into the combustion chamber. Clogged fuel injectors are more common in diesel engines than gasoline engines because diesel engines tend to produce a lot of soot that can clog the fuel injector.

keyboard_arrow_right Faulty mass air flow (MAF) sensor

The MAF sensor is responsible for measuring the amount of air entering the intake air manifold. If the PCM lacks accurate information regarding this amount, it can end up with a rich air-fuel ratio.

keyboard_arrow_right Faulty fuel pressure regulator

The fuel pressure regulator makes sure that fuel is flowing properly to the fuel injector even when there are dramatic fuel demand changes. A faulty fuel pressure regulator can result in an excess amount of fuel being burned.

If your vehicle is producing black smoke, then soot deposits will build up in the exhaust and engine. This is more likely to happen in diesel vehicles. Soot is the powder-like substance that makes exhaust fumes black. Soot buildup can cause problems in other parts of the engine, like the catalytic converter, oxygen sensor, and EGR valve.

Smoke Color
Diagnosis
Possible Issues
thin white smoke Thin White Smoke
Normal
None
thick white smoke Thick White Smoke
Not Normal
  • Blown Head Gasket

  • Cracked Block or Cylinder Head

blue gray smoke Blue or Gray Smoke
Not Normal
  • Damaged Piston Rings

  • Worn Cylinder Walls

  • Faulty Turbocharger

  • Faulty Valve Stem Seals

  • Bad PVC Valve

thick black smoke Thick Black Smoke
Not Normal
  • Clogged Fuel Injector

  • Faulty MAF Sensor

  • Faulty Fuel Pressure Regulator

conclusion background

If your vehicle is producing a lot of smoke, then it means that its engine is running inefficiently and producing more tailpipe emissions. You shouldn't allow these issues to persist because aside from hurting your vehicle, they’re also a threat to public health and the environment.

Vehicles tend to produce more poisonous gases, such as nitrogen oxide, hydrocarbons, and carbon monoxide, when they run inefficiently. This is the reason why some states have periodic, government-mandated emissions tests in urban areas. Aside from being toxic, these gases are also a major cause of climate change.

Adverse Effects of Excess Smoke

A change in exhaust smoke color is an indicator that there's something wrong with your vehicle. Now that you know the possible issues that can cause a specific smoke color, you'll have an idea of which parts you need to check. You should make sure that all your vehicle's engine parts are well-maintained to prevent it from emitting harmful colored smoke. By maintaining your vehicle's engine, you can reduce emissions and ensure your ride is roadworthy.

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