I have used amsoil for about 20 years now, i have always driven 80 % highway and 20% city and run the oil for 25,000 - 30,000 miles and have never had engine problem related to oil. I do change the oil filter about ever 5000 miles and top of oil. I use nothing else including 2 cycle amsoil. most every vehicle I own had over 100,000 miles when I purchased and now have close to 200,000. and still run great with no engine issues.