Diagnosing Grey Smoke From Diesel Exhaust When Accelerating

Heavy duty diesel engines can run for millions of kilometres with the right maintenance schedule. Simple construction and tough internal components mean that diesels are unlikely to fail all of a sudden.

But, diesels still need servicing, and the colour of the exhaust can tell you a lot about the condition of the engine. Black, white, blue or grey diesel exhaust can all indicate that something is wrong with the vehicle.

Diagnosing unusual exhaust colours can be a challenge. It’s normal for your exhaust to have a slight colouration at times, and each colour can represent a handful of different issues. In this article we’ll discuss diagnosing black, white, blue or grey smoke from your diesel exhaust.

White Smoke From Diesel Exhaust

Diesel engines may blow white exhaust.

If you live in a cold climate and your exhaust produces a thin, white smoke when you first start the vehicle, this is caused by a form of condensation. This usually isn’t a problem if the smoke goes away within a few minutes.

Thicker clouds of white smoke that don’t fade away after running the engine indicate much bigger issues.

White smoke from a diesel exhaust can be caused by:

  • Blown head gasket

  • Damage to the engine block or cylinder head

  • Low cylinder compression

  • Unburnt fuel making it to the exhaust

  • Failing glow plugs

  • Faulty injectors, injection timing or problems in the fuel line

It’s common for diesels that are blowing thick, white smoke to also run poorly. If the engine seems lumpy, sluggish or low on power, switch it off and contact your diesel mechanic. Running an engine that is blowing white smoke can cause serious damage.

Blue or Grey Smoke From Diesel Exhaust When Accelerating

Blue or grey smoke when accelerating is one of the most common complaints on diesels. These two colours of exhaust smoke are actually caused by the same thing: the engine burning excessive amounts of oil.

In all engines, oil is used to lubricate internal components. Small amounts of oil are burned during normal operation. If the engine starts burning too much oil, the exhaust may look blue or grey, depending on the severity of the issue.

It’s fairly common for diesel engines to blow blue smoke in cold climates. If the smoke goes away once the engine has warmed up, there’s no need to panic. If the blue smoke persists then you need to contact a mechanic.

Blue or grey smoke from a diesel exhaust can be caused by:

  • Low cylinder compression

  • Worn valve seats and springs

  • Worn piston rings

  • Worn injector seals

  • Failing turbo seals

  • Sticky PCV valves

Your mechanic can perform a simple compression test to determine where the problem is located. Engines that burn large amounts of oil may need to be rebuilt, or the head may need to be rebuilt. This is a large task, but rebuilt components can deliver years of trouble-free operation.

Black Smoke From Diesel Exhaust

Small amounts of black smoke are normal for diesel engines. Black smoke contains carbon particles, hence its colour. Excessive amounts of black smoke usually indicate that something is wrong with the fuel combustion system.

Black smoke from a diesel exhaust can be caused by:

  • Worn turbo seals

  • Incorrect timing

  • Incorrect fuel/air ratio

  • Dirty air cleaner

  • Dirty intake manifold

  • Failing injectors and incorrect injector timing

  • Low quality fuel

  • Low cylinder compression

  • Carbon build up in the cylinder

If you notice black smoke coming from your diesel exhaust, put the vehicle in neutral and increase the engine speed. Watch the amount of black exhaust as the RPMs increase. While small amounts of black smoke are normal, the exhaust should be mostly colourless as the engine heats up and as you accelerate.

Don’t Ignore an Abnormal Exhaust, Get Your Vehicle Inspected by KS Mobile Diesel

The colour of your diesel exhaust can tell you a lot about how well the engine is functioning. While it’s normal to see small amounts of white, grey or black exhaust under normal use, excessive smokiness can be a sign that something is seriously wrong.

If you’re concerned about the colour of your diesel exhaust, book an inspection with KS Mobile Diesel. KS Mobile Diesel is a mobile diesel mechanic based in Caboolture. We work all over the Brisbane region, providing inspections, maintenance and repairs for diesel vehicles and equipment.

Our mobile fleet is equipped to service light and heavy trucks, Buses, trailers, earthmoving and agriculture equipment, 4WDs and much more.
Contact us today to book an appointment. We’ll come to you and provide full diagnostics, maintenance and repairs!

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