Oil Change - Mileage or Percentage?

[hatzie]

Originally Posted by jocko

I’ve changed the oil in my 5.3 every 3k since new - it now has 304k miles on it, never been apart. I used conventional oil for about the first 275k until I could no longer find it for sale locally, so switched to synth blend. Always 5W30. Maybe it’s overkill, dunno. Don’t like how expensive it’s gotten to change one’s own oil - makes me wonder what crap the oil change shops are using to be able to charge about 2/3 of what it costs me to do it myself - they need to be able to make some profit too, so they must be getting a heckuva good deal on bulk oil.

Likely they're using super cheap oil and filters.
I'll keep changing my own. I know what's being poured into the engine and what filter is being used.