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Guys, i noticed that after i changed my engine oil to lower viscosity grade 10w-40 HKS semi-syn , i can hear the rougher the valves sound come out from the rocker head...how come huh ? does it harmful to the engine ? previously i was using AMOIL turbo plus oil, but not so sure whats the grade d..but confirm not semi-syn wan...im using e2 63T engine now currently...pls advise...thanks in advance...