i use that new synthetic Q stuff, and I have noticed a difference, oh yeah I also use napa filters

 

ya i use the same as 19stang66 mobil or Valvoline 10W-30 every 2-3k or if it sits for over a month i change it before i drive it again

 

it depends since it so damn hot here in the summer i use 20w-50 with a bosch, K&N, or a Napa (depends on where i am)
and in the winter i use rotella with either of those filters

 

'01 focus ZX3-- full synthetic 10w30 and top quality filter every 4k

'65 Comet with ~350hp 302-- full synthetic 10w30 or 10w40 and K&N filter every 2k

'67 F-250 6 cyl-- valvoline 10w40 dino with anything but Fram filter every so often

 

Assuming that its a stock engine, my vote goes for 10W30 or 10W40 every 3,000 miles or 3 months whichever comes first. The older engines require more maintenance. Get into the 50's and your talking new oil and filter every 2,000 miles. Prior to filters, new oil every 1,000 miles. As time has gone on, the tolerances on the engines has gotten much better so fewer contaminants get in the oil and the oils have become better at dealing with contaminants. Like religion and politics, when you start talking oil with car guys, just about everybody has a favorite and they'll probably defend it to the death.

 

Amsoil 10W-30 seems to work well.