Ok, I know all this is personal opinion but thought i'd throw it out there......myself I am a valvoline man but now that i own a twin engine boat with 7.3's thinking about just using Napa brand....My buddy works there and can get it pretty cheep. Being im gonna need roughly 17 qrts, and did some research its bottled in ashland ky by guess who??? yes, Valvoline, I thought i'd consider it. Now, is it the same formula....no body knows. I did think about running some lucas additive. whats everyones take on the matter??

oh, sorry 780 hrs. gonna use 30w. previous owner used castrol gtx. Not a big fan!

I use valvoline 40wt

30w seems a little light. I would say 40w if using straight weight, as long as the brand you want to use has the proper ratings.

http://www.mercurymarine.com/service...?category=fuel

Waaaaayyyyyy More important than the Type of oil you use is how often you change it & be sure there is always enough in there. Most Bargain brands (Napa, Valvoline Etc) have about the same proctective ingredient packages, some last longer than others but I don't let mine stay in there long enough to find out. I used to be a believer in Mobil 1 until they took out 80% of the good stuff then I quit using synthetic all together. I'm sure royal purple is great stuff but I don't leave my oil in long enough to justify the cost.

Kendall GT-1 20w50

i thought the engines (merc7.3) called for 30 weitht?? maybe it does call for 40wt. Have to check this out.

well, it does call for 40w at the temps i run in, it needs to be 40w!

Mobile 1, 15-50W Syn

Amsoil 15W-50 with Blackstone oil analysis every change