Grew up working in my uncles gas station garage and was firmly taught to change my oil every 3k, did that for years and had great results.
When I bought a new 4x4 in 2004 the manual stated 4500 and I have done that using standard oil for the past 315000 miles, again with great results.
Have a 2018 4x4 on order and it will be my first car to run synthetic oil.
if Mobil 1 is as good as they claim I will be happy.
