The color of exhaust gas slightly differs from vehicles, but is usually divided into colorless, white, black, and blue-gray. Therefore the color of gas emitted from a car’s muffler shows the condition of engines and the cause of failures. Then how does the cause of failure differ according to the color of exhaust gas?

First, colorless (invisible to the naked eyes due to shimmering)
If the exhaust gas is colorless, the vehicle’s engine has no problem. It indicates that the engine works normally to burn oil. Colorless or slightly light blue colored gas represents that the engine is normal. 

Second, white color​

White-colored exhaust gas emitted indicates that the engine is not properly ignited due to low temperature. This white color is created by incompletely combusted fuel particles, but this phenomenon disappears if the engine temperature increases. In winter, normal engines can produce white-colored exhaust gas. This is vapor produced during combustion and it’s like white breath coming out from the mouth. Much vapor is produced if hydrogen is contained more based on the ratio of carbon (C) and hydrogen (H) in fuel. That’s why the exhaust gas from buses (CNG) or taxes (LPG) in winter look white. Sometimes the abnormally increased amount of moisture is produced from the muffler in winter. It often happens when the vapor out of emissions is rapidly cooled as a hole is made in the muffler, so it is needed to check the muffler’s state.

Third, black color
Exhaust gas has black color when thick mixture gas is supplied or relatively insufficient combustion air is provided. Black color is created as incompletely combusted carbon gas comes through exhaust gas. It is because an excess of fuel is sprayed due to the defected injection pump or air is not supplied smoothly due to the air filter blocked by foreign substances. Inspection is needed. 

Fourth, blue-gray color
Blue-gray color is created due to incomplete combustion. As gasket is damaged or a piston oil ring is worn out, engine oil is inflowing to a cylinder through a crack caused by wear and burns with fuel. Here blue (additive ingredients) and grey (distillates with high boiling points) colored gas is emitted. Generally the gas emitted when engine oil burns with fuel is said to be white, but precisely it is blue gray. If the blue gray colored gas is seen, it is needed to call the car in the maintenance shop and check if there is any problem with engine system including a piston ring and a cylinder head.

Therefore it is important to do a thorough check of the vehicle with great interest and avoid excessive driving in order to maintain the vehicle in good condition for a long time.