What Causes Oil Blow Back From Dip Stick?


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The blow back from the dip stick is caused by "blow by". Blow by is leakage of combustion exhaust gases past the pistons.

All engines, even new ones, have a certain amount of blow by. Blow by is controled by the PVC (Positive Crankcase Ventilation) system. Since these gases are just like any other exhaust gas the PVC system is an important part of the emission control system. It is supposed to direct the gases back into the engine to be burned and then disposed of by other parts of the emission system.

If an engine is worn out there will be more blow by which can overcome the PVC system. So too much blow by is a sign that the engine is worn out.

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