Engine sludge is a phenomenon that can affect almost any engine.

It first began to appear in Australian vehicles in the late 1980s and can cause extensive engine damage.

What is it?

The term describes the formation of heavy deposits in an engine’s crankcase. 
  • It can resemble heavy grease or tar and results from the thickening and oxidation of the engine oil 
  • The resulting material blocks the engine’s lubricating system
  • In the worst case this can cause the engine to seize

What causes it? 

  • Its formation can usually be traced to inadequate servicing, such as missed or extended oil change intervals or to the use of poor quality or inappropriate oils 
  • In small diesel engines, as used in light commercial vehicles and 4WDs, fuel system problems, such as worn injectors, can also thicken the oil

How to deal with it 

  • The appropriate remedy must be determined on a case by case basis 
  • In many cases the presence of sludge is not detected until the engine has failed 
  • In such cases, dismantling is required to identify the extent of damage and carry out repairs, which will also include removal of the sludge.  Often this will involve complete reconditioning of the engine
  • Where the problem has been identified before the engine has failed, it may be possible to remove much of the sludge without completely dismantling it  

Warning signs

  • Low oil pressure or intermittent flashing of the oil light 
  • The oil light remaining on when the engine is running
  • Slow or no draining of the oil when the sump plug is removed (sludge is preventing the remaining oil from draining) 
  • Obvious signs of thick sludge in oil fillers, rocker covers etc. 
  • The engine won’t accept the designated amount of oil after an oil change (sludge is taking up some, or most, of the oil space)
  • Noisy hydraulic lifters (where fitted)

How to avoid sludge problems

  • Engine sludge can be avoided with regular servicing in accordance with the manufacturer’s specifications
  • Use appropriate, good quality oils and filters 
  • For diesel engines, fuel system maintenance is critical
  • Follow the manufacturer’s instructions concerning city driving.  Most regard this as severe use requiring more frequent oil and filter changes 
  • Severe use oil change intervals can be as little as 5,000km to 7,500km
  • Don’t ignore oil change time intervals. Oil changes are still needed even if the vehicle hasn’t travelled the nominated distance