Fuel Dilution
The presence of unburned fuel in crankcase oil can seriously retard its performance in a number of ways. For example, the thinning of the lubricant can lead to decreased film strength which results in abnormal wear. Fuel dilution of as little as 5% will reduce the viscosity of SAE30 oils to the equivalent of SAE20. Typically, dilution values greater than 4% (by volume) are considered to be at immediate corrective action levels.

Causes Effects
Incorrect fuel Metal to metal contact
Extended idle Poor lubrication and thinning oil
Stop and go Driving Increased overall wear
Defective injectors Cylinder ring and bearing wear
Leaking fuel pump or lines Decreased additive effectiveness
Incomplete combustion Risk of fire or explosion if fuel dilution is very high
Incorrect timing Reduced fuel economy
  Shortend engine life
Recommendations
Check fuel lines and look for worn rings, leaking injectors, seals and pumps
Analyse operating techniques
Check timing
Evaluate equipment suitability for application
Change oil and filters

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