Crankcase Dilution:
Crankcase dilution occurs when the fuel that is not
vaporized leaks past the piston rings and seeps into the crankcase. The
vaporized fuel then dilutes the engine oil, reducing the lubricating qualities.
A certain amount of crankcase dilution occurs in all engines during warm-up. It
is not considered harmful in normal quantities because it vaporizes out of the
oil as the engine warms up. The vapours then are purged by the crankcase
ventilation system.
Carbon dioxide, Nitrogen, Water and Traces of Combustion
of fuel . When the engine is running, some part of these products may leak
through the piston rings to the crankcase . This causes dilution of oil in the
crankcase .Corrosion of crankcase metal, piston pins,, cylinder walls and timing
gears may also result because of this .
Keeping engine oil at the proper level is important.
Over time, the engine oil level drops; either because of the leaks or because
some amount of oil gets burned in engine combustion chambers. Driving with very
low oil level can cause problems.
Crankcase dilution can be caused due to:
• Leaking injectors
• Excessive idle time
• Incomplete combustion
• Engine operating in cool conditions
• Frequent short trip driving
• Restricted air filter/bad air to fuel ratio
• Worn piston rings/excessive blow-by
• Incorrect choke settings
• Over fueling
• Damaged seals and gaskets
• Improper injector timing
The following can occur due to crankcase dilution:
• Reduction of oil viscosity
• Disruption of oil film resulting in engine wear
especially in the cylinder ring area.
• Increase of volatility- in extreme case it can
cause crankcase explosion.
• Weakness of lubricant detergency
• Accelerated oxidation of lubricant.
• Formation of varnish.
• Formation of acid and corrosion.
• Decrease of oil pressure.
Depending of the application and operating
conditions, a limit of up to 2% fuel dilution may be allowed provided viscosity
has not changed. However, It is recommended to examine the engine and analyze
operating conditions. Dilution ranging between 2.5% to 5.0% is considered
excessive and requires immediate maintenance action.
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