On Sun, 16 Jun 2019 08:24:53 -0500, dpb wrote:

On 6/16/2019 7:58 AM, 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?

Follow manufacturer's recommendations.
If you use penzoil, change every 3000. Same with Quaker State.
Using a more highly refined oil with less parafins (Like Castrol GTX)
go 5000. Or use synthetic and go 10,000.

Really - it's not just mileage - it's how the miles are put on - short
trips, high temperaturs, al kinds of things come into play.