On Sun, 16 Jun 2019 05:58:37 -0700 (PDT), wrote:

My mechanic likes to use Castrol extended and change oil every 5000 miles. I have alway s used Pennzoil 10/30 and changed oil every 3000 miles. which one is right? Or both of us right? Whaddaya think guys?

I think you are wasting oil.
3000 miles is far too frequent.
When was the last time you heard about an oil related engine failure,
even with people who run the same oil for a couple of years?