Hi, I have a 1991 Nissan SR20DE engine with 211,000mi. API SG, 5W-30 is the recommended weight according to the service manual, but with high miles I was advised to run 10W-40. I have been running 10W-30 and 10W-40 Castrol GTX and changing it every 3000 to 3500 miles.
I believe it has a bad...