Family member has a 2009 RX 350 with 75k miles. The engine has a knock noise and sounds like diesel. Vehicle previously got its oil change in quick lube shops around every 3k miles and I seriously doubt they done everything correctly. Filter was extremely filthy with small amount of sludge on it when I did oil change on this vehicle at 65k miles.
I I have done 4 oil changes in the past 10k miles using full synthetic 5w30 oil but problem still exist. I am thinking using liqui moly engine flush. No check engine light so far but knock noise still exist. Following link has the same engine knock noise in the rx350.
How much life do you think this engine still have? Is there anything I should try first at this point? Thank you so much!