Checking my oil earlier, engine block sticker says to use 5-30 hood sticker says the same. Ford dealer always uses 5-20 internet auto zone orielys all recommend 5-20. Who's right?
2000 F250 6.8 v10

I been told and believe that in these newer engines thinner is best, because of the small oil journals they use.

Always ran 5w20 in my 2001 v10 and its over 275000 iles

Same here w/292k all my buddy used too (he was original owner) That is why I found it interesting. He only serviced it at Ford too

I think my fill cap has 5w20 on it

all my fords since 99 have taken 5w-20

my GMC takes 5W-30

I don't know specifically abotu the V10 but the 5.4 v8 and I have had 3 of them are all 5w-20 the 3rd one is getting close to 200k the first 2 where going strong when other things happened at 245 and 270K

I’d look in the manual and use whatever it says for that engine.

Wife’s Rave 4 takes 0W20

Nvw my oil cap just says oil lol.
Keystone if I remember right it gives a range of acceptable oil.
GCP that's my understanding from 99 on

I put Rotella 10W30 into everything from my truck, the admirals car to the tractor and wood splitter and everything else that has a foursmoke engine in or on it and it works or me.

The new ones are now 0W16.

My Ford likes 15w40