What Your Diesel Smoke Colour Means

Knowing how to spot and diagnose issues with your heavy-duty engine early on is the best way to prevent unwanted downtime and costly repairs later down the line. One of the best ways to identify an engine problem early on is monitoring the smoke colour coming from your exhaust. Whilst some smoke is common when you start up, a well-maintained engine shouldn’t emit any visible smoke during operation.

The colour of any exhaust smoke can tell you a lot about the potential problems causing it. There are three colours you might see; black, white, and blue. This article will explain what each colour indicates for your engine and how you can resolve it.

Black Smoke

Black smoke is the most common smoke colour and is often the result of a very rich fuel-to-air ratio. It indicates something is wrong with the combustion of fuel, which can often lead to an increase in the emission of greenhouse gasses such as carbon dioxide.

There are several potential causes for this, such as too much fuel getting injected into the engine which it can’t burn. It could also be the result of restrictions in the intake/exhaust. General poor maintenance, such as the air cleaner not being properly maintained, can also be a contributing factor.

The first place to look when identifying the issue is the fuel system to make sure the right amount of fuel and air is being delivered.

White Smoke

Unlike black smoke, white smoke indicates a lower concentration of carbon exhaust particles and is often caused by unburned fuel going through the exhaust. This can be common during colder weather as frozen deposits of soot that have expanded around rings are burnt away as the engine warms up.

If this is the case, the white smoke should clear very quickly as the engine heats up. On older engines, using glow plugs during cold starts is highly recommended to prevent this, especially engines with low compression or low injection pressure. Using fuel with a low cetane rating can also cause white smoke, as the diesel fuel will not ignite as quickly when you inject it.

Making sure the injectors are not damaged should be the first course of action, as well as checking for damage to rings or cylinder liners and cracks in head gaskets or the cylinder head causing water to mix with the diesel fuel in which case the white smoke could be mixed with steam/water vapour(CJ).

Blue Smoke

Blue smoke is the least common colour of smoke, and is most often the result of excessive oil consumption. This can occur in cold weather as oil thins out and escapes into the cylinder to be burnt. It may also happen as worn rings unseat slightly and the seal between the combustion chamber and crankcase is not completely sealed.

If you notice blue smoke, be sure to check for damage or wear to your piston rings and cylinders as well as for an overfill of the engine with oil. Wear can also occur in the valve guides, oil seeming down into the cylinder.

If you encounter sudden excessive smoke of any colour, turn off the engine to prevent potentially causing serious damage. If the engine has a monitoring system, check for any fault codes to help identify any issues.  If you find the cause of the smoke is damaged or worn engine parts, you will need to replace before they cause further problems.

At Jaytrac, we supply heavy-duty replacement parts for a range of machinery, including fuel injectors, seals & gaskets, and other engine parts. To find out more, get in touch with us today by calling us on 01604 491 133 or emailing us at sales@jaytrac.co.uk. Alternatively, use our online enquiry form to send us the exact details of what you need and a member of our friendly team will get back to you.