86 tempest, viscosity question

[on_plane]

Hi ,
I just picked up an 86 18' with a 300hp tempest 350sb that has 300 original hours and has been meticulously maintained. I have the manual and it calls for SAE 30W oil. Is this the correct oil to use or is there a better choice with todays newer oil? I know current mercs use 25w-40 and waswondering if that would be a better chice. I boat in North Texas, it can get 'fairly' warm at times :eek!:
I plan on sticking with conventional oil for now, any real good reason to switch to a synthetic if I keep the engine temp in line? Plan on adding new stainless marine manifolds and risers along with their crossover kit as the manifolds are 20 years old even though always in fresh water...
Many thanks,
Paul

[BigGrizzly]

I can answer the oil question from reality not from the Merc manual. That engine ran fine for years on 30w. the 25/40 is a new viscosity as of a couple of years ago. It is no better then what is recommended or your motor. All oils get a API status which is what you look for in the can. Remember oil to day is better than oil in the 1980s. Me I use the 30 in 0ne boat and 20w50 in the other. I have done oil testing for years at Honda, so I prety much know all the answers.