What Causes Grey Smoke from a Diesel Engine?

Diesel engines are often used in trucks, buses, and trains. Sometimes grey smoke comes out of the engine instead of white or black smoke. The grey smoke from a diesel engine can be caused by many different things. We will discuss the most common causes of grey smoke and how to fix them.

How Does Diesel Work?

How does diesel workWhen diesel burns inside the engine it creates heat and pressure which give the energy to turn gears or move an electric generator. But there’s something else going on too: when diesel burns during combustion it produces grey smoke as well as white smoke. The grey particles are soot – small, dark bits of carbon that come from burning oil products such as gasoline or waxes found in coal tar.

Causes of Gray Smoke from the Exhaust Pipe of a Diesel Engine

Grey smoke coming from a diesel engine is not only ugly to look at, but it can also be dangerous. What causes grey smoke from a diesel engine? There are many potential answers to this question. The grey smoke could result from an ignition problem or the fuel might have collected too much oil and grease, or coolant that has leaked into the combustion chamber and ignited due to excessive heat, or there are not enough air pockets in the combustion chamber.

What You Need to Do

Whatever the cause may be, grey smoke should never be ignored! Luckily all these causes can be fixed with just a few simple steps that you should try before taking your vehicle to get repaired!

  • What you need to doCheck for any loose wires around the distributor cap
  • Remove excess oil and dirt buildup on electrodes near the spark plug
  • Add some extra air to combustion chambers
  • Clean out oxygen sensor (depending on age)
  • Replace worn parts/lubricate moving surfaces with lithium-based lubricant

If grey smoke from a diesel engine is occurring, it may be due to one of these causes. If the problem persists after following all these steps, consult with your mechanic!

Another Sign to Look Out for

The grey smoke coming out of the vehicle’s exhaust smells terrible and something more serious might be going on! When you see greyish-white plumes billowing from under the hood instead of white or black ones, there could be many things happening. The smell will vary depending on this cause too. For example, if air pockets are not present in combustion chambers then this can make for an unpleasant odor while driving around town because it creates higher levels of unburned hydrocarbons and carbon monoxide.


When grey smoke coming out of a car’s exhaust one cause could be an ignition problem, the fuel having too much oil and grease, another reason for greyish white plumes billowing would be a lack of oxygen in combustion chambers (which can occur when there isn’t enough air flowing inside). Other problems like poor ventilation will create higher levels of unburned hydrocarbons and carbon monoxide. These all have simple fixes though. But if you have followed the few steps that we suggested, but the problem has not disappeared, then you should contact your mechanic. Don’t ignore this serious problem!

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