I really don’t want to open another can of worms, just wanted to find out for myself.
My 2001 Mazda MPV has 5W20 for recommended oil. Does the fact that I live in So California and temperatures are higher then 60F most of the time allows me to use 5W30 or 10W30 oil instead? And a friend of mine has this strange theory that if you fill oil to the top mark i.e. full, it will cause the camshaft to hit the surface of the oil all the time and cause internal drag on the engine... ? My take on this is, he's just trying to save another quart of oil, because if what he says would of been true, oil would be foaming all the time, wouldn’t it? Thanks

 

I wouldn't deviate from the manufacturer's recommendations on oil weights at all. Although the 5W30 or 10W30 isn't much of a difference, the tolerences are engineered for a specific weight no matter what climate. The hot weather/cold weather differences are a thing of the past now. Where I live it runs 90 plus degrees more than half the year and it's still required to stay with manufacturer's recommendations.
As far as your buddy's dumb ass theory, it's just that! Leaving the oil level intentionally low can starve the pick-up in certain situations and do serious damage. The camshaft is far away from the oil level.

 

He said camshaft but surely he meant crankshaft.

If your friend thinks he is smarter than the manufacturer's engineers he shoild get a job there!

 

If he doesn't think the crank should touch the oil, how does he think the cylinder walls are going to get lubricated.

 

thank you thank you thank you! I thought I am going mental here...