SHOP MANUAL
Engine
Ch 1 page 156
Oil mist separator
General
A certain amount of oil is always found in the crankcase gases, and this is normal. The amount of oil mist in-
creases with the engine’s operating time.
The closed crankcase ventilation system is very sensitive to changes in the flow of crankcase gases in the
engine.
If the flow of crankcase gases increases, the amount of oil which passes through the crankcase ventilation also
increases. The crankcase gases can then take with them small drops of oil from the crankcase.
The causes of too high a flow of crankcase gases can be difficult to determine, and troubleshooting must there-
fore be carried out methodically.
When the flow of crankcase gases is too high, the primary symptom is an increased amount of oil mist.
If the engine’s oil sump is filled with too much oil, or if the oil cannot be separated, oil will be sucked up with the
crankcase gases.
Faults which can arise in the engine and which are caused by the oil mist separator fall into 3 different catego-
ries:
• Too high a flow of crankcase gases
• Increased crankcase pressure
• Increased amouts of oil carryover
High levels of oil carryover
High levels of oil carryover mean large amounts of oil coming from the crankcase ventilation. High levels of oil
carryover are often due to excessive amounts of oil entering the crankcase ventilation, and the oil can therefore
not be separated quickly enough in the oil mist separator. There may also be a blockage in the return pipe for
the separated oil.
Common causes of levels of oil carryover being too high:
• Worn rocker arm shafts on cylinder 6 (cylinder 5 on five cylinder engines).
• Too much oil in the oil sump.
• Gas leakage at valve guides, particularly during exhaust braking.
• Internal oil leakage.
• Blockage in the return pipe for the separated oil.
Fault causes,
The most common faults when there are problems with crankcase gases. See table next page.
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