I’ve always used the rule that if you use new oil, you can go further between changes and if you let the local quick lube type place use the bulk oil, that abour 3000-4000 is right, since they are using recycled oil. any comments?
I don’t know anything about quality variations among bulk oils though I will let a synthetic get older before even checking it.
Every Haynes or Chilton book I’ve seen says to look in the car’s User’s Manual or under the hood. I’ve seen “7,500 miles” on Hondas and Toyotas for sure since the very early 1980’s.