Why waste the oil use it. I bought a 1980 Accord in the mid 80s with 86,000 miles on it. Previous owner only used 10w 40 on it since new. I did the same used 10w 40 year around with 3000 mile OCI. Drove it to 186,000 miles before I sold it. It was still running with nothing but 10w 40 in it new thru 186,000 miles. I find it hard to believe its going to hurt the motor with 10w 40 in it.