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