"I agree 50 weight oil is too thick for 95% of the cars out there. The lash adjusters in a lot of DOHC engines will work poorly with that thick of an oil and can cause oil pressure issues." Show me the data. In G0d I trust, all others send data. Before you do remember my Mazda has passed 250,000kms and ran 25W70 for many years. Never had the head off.