Wear on pistons, piston rings and cylinders caused by fuel flooding


  • Severe signs of wear on the piston top land and piston skirt.
  • Friction marks on the piston skirt, characteristic of dry running due to fuel flooding.
  • Piston rings display severe radial wear (Fig. 1). Both webs (support surfaces) on the oil control ring have been worn down (Fig. 2). By way of comparison in Fig. 3: profile of a new and worn oil control ring (double-bevelled spiral expander ring).
  • Increased oil consumption.


Fuel flooding due to abnormal combustion always damages  the oil film. This leads to a higher level of mixed friction and increased radial wear on the piston rings within a short period. The characteristic fuel friction only occurs after the oil film has been so badly impaired by the fuel that lubrication is then insufficient (refer to the chapter entitled “Dry running damage due to lack of lubrication caused by fuel flooding”). The increasingly ineffective lubrication results in high levels of wear on the piston rings, piston ring grooves and cylinder sliding surfaces.

In the initial stages the piston skirt is damaged to a lesser degree, as it is regularly supplied with new oil that is still capable of providing lubrication from the crankshaft drive. Once the abraded particles from the moving area become mixed with the lubricating oil and the lubricating oil loses its load-bearing ability as a result of increasing oil dilution, the wear will spread to all bearing points in the engine. This affects the piston pins and crankshaft journals in particular.

Mögliche Ursachen

  • Frequent operation over short distances and resulting oil dilution with fuel.
  • Coolant admixture in engine oil.
  • Poor engine oil grade.
  • Fuel flooding due to incomplete combustion as a result of malfunctions in the mixture preparation.
  • Malfunctions in ignition system (misfiring).
  • Insufficient compression pressure or poor filling through worn or fractured piston rings.
  • Incorrect piston protrusion dimension: the piston strikes against the cylinder head. On diesel engines with direct injection, the resulting vibrations cause uncontrolled injection of fuel from the injection nozzles and thus fuel flooding in the cylinder (refer to the chapter entitled “Impact marks on the piston head”).
  • Poor filling through clogged-up air filter.
  • Faulty and leaking injection nozzles.
  • Faulty or incorrectly set fuel injection pump.
  • Incorrectly routed injection lines (vibrations).
  • Poor charging through faulty or worn turbocharger.
  • Poor fuel quality (poor self-ignition and incomplete combustion).