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Q: Extremely low oil & knocking noise

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Out of the blue a knocking noise started coming from the engine so i checked the oil levels and it was completely out of oil, and there is no leak in the system at all so the oil was burned. I was wondering if I could possibly be the PCV valve because of low oil pressure, any other ideas?

My car has 140000 miles.
My car has an automatic transmission.

If the engine is to the point of making knocking sounds, there is probably internal damage at this point due to the low oil level. If the crankshaft is scored from lack of oil, then oil pressure will not return no matter if the PCV system if good or not.

Your least expensive course is to have a shop or one of our mobile technicians come diagnose the reason behind your low oil level. If the engine is internally damaged, it would not make sense to start replacing parts that may not help your situation.

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