Engine oil analysis – Soot generation & Fuel (diesel / gasoline /petrol) contamination e.g. with leaky injector or worn cylinder rings.

Soot – This is a normal process of the fuel combustion process. This is a good indicator of combustion efficiency in the engine and should be monitored as part of any diesel engine analysis package.

Common CausesPotential ResultPotential Advice
High Soot / insoluble
  • Poor fuel quality
  • Low compression
  • Worn / badly sealing engine rings
  • Defective spraying
  • Improper air/fuel ratio
  • Excessive oil hours
  • Engine gelling and seizure
  • Poor fuel efficiency / mpg
  • Blogged filters
  • Reduced filter life
  • Increased wear
  • Carbon deposits.
  • Change oil
  • Change filters
  • Assess if drain intervals need changing
  • Reduce excessive idling
  • Check air induction and turbos working correctly.
  • Check injectors not excessively dosing system.

Diesel Fuel  – This can be provided as a normal, caution or serious result based on flash point, or as a percentage dependent on your test suite type. Excessively high fuel dilution may also pose a fire risk. Diesel systems converted to run on biofuels such as B20, B80 and B100 the fuel dilution can be provided as a percentage FAME (Fatty-Acid-Methyl-Ester) content.

Common CausesPotential ResultPotential advice
High Fuel dilution
  • Excessive idling
  • Injector fault
  • Incomplete combustion
  • Stop start operation
  • Incorrect air to fuel ratio.
  • Excessive cylinder and ring wear
  • Metal to metal contact as lubricant removed by “fuel wash”
  • Reduced mpg
  • Decreased engine life
  • Reduced engine performance


  • Check for leaking injectors.
  • Check timing.
  • Replace worn rings
  • Submit sample of fuel for testing