How to Identify the Problem with a Smoky Diesel Generator

How to Identify the Problem with a Smoky Diesel Generator

By Tinuola Ann Ajayi

As part of its contribution to ensure you enjoy your investment in power, Joshua Long Consulting presents its “prolong the life of your diesel generator” series with the focus today on generator smoke,

Basically, smoke from a diesel engine indicates that something is not right , this will potentially shorten the engine life, or result in unnecessary costs.

A diesel engine in good condition should produce no visible smoke from the exhaust, under most operating conditions. A short puff of smoke when an engine is accelerated under load may be acceptable.

There are three basic types of smoke, as identifiable by their colour.

1. Black smoke is the most common smoke emitted from diesel engines. It indicates poor and incomplete combustion of the diesel fuel. There are many causes, including

  • Incorrect timing
  • Dirty or worn injectors
  • Injectors sticking open too long
  • Over-fueling (yes this is possible)
  • Faulty turbocharger (ie not enough air to match the fuel)
  • Incorrect valve clearance
  • Incorrect air/fuel ratio
  • Low cylinder compression
  • Dirty air cleaner
  • Carboned up intake manifolds
  • Other engine tune factors
  • Poor quality fuel
  • Excessive carbon build up in combustion and exhaust spaces
  • Cool operating temperatures


2. Blue smoke is an indication of oil being burnt. The oil can enter the combustion chamber for several reasons.

  • Worn valve guides or seals
  •  Wear in power assemblies (cylinders, piston rings, ring grooves)
  •  Cylinder glaze
  •  Piston ring sticking
  •  Incorrect grade of oil (eg oil too thin, and migrating past the rings)
  •  Fuel dilution in the oil (oil thinned out with diesel)


3. White smoke occurs when raw diesel comes through the exhaust completely intact and unburnt. Some causes of this include

  • Faulty or damaged injectors
  • Incorrect injection timing (could be a worn timing gear or damaged crankshaft keyway).
  • Low cylinder compression (eg caused by leaking or broken valves, piston ring sticking, cylinder and/or ring wear, or cylinder glaze)
  • Water entering combustion spaces will also create white smoke.

Did you find this write-up to be informative? Please give us your feedback.

Tinuola Ann Ajayi is the Head Sales & Marketing, she can reached on Twitter via @joshualong2016 and


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