which Octane is the best for a 1986 75 hp merc

[Myke48]

I have been hearing all kinds of stories about which octane is the best to use,,,,,1st discussion is a 1986 75hp merc was built to run on low octane,and that hi octane will ruin the engine because it burns hotter,,,,then I was told that if I use 87 octane my motor would only run on 2 pistons,??? that seems far fetched to me,,,,only 2 pistons,,supposedly a safety mode????,,thanks,,Mike

 

[JB]

Re: which Octane is the best for a 1986 75 hp merc

Use 87. If it won't run on that it won't run on anything.

 

[Barnacle_Bill]

Re: which Octane is the best for a 1986 75 hp merc

What JB said. I've always ran 87 octane in my 75 and 150 mercs. Using high octane is a waste of money. Your motor does not need it.

 

[Myke48]

Re: which Octane is the best for a 1986 75 hp merc

Thanks guys,,,I am trying to get the fuel system right and so far this place has helped get it straght,,again thanks,,,Mike

 

[gregpro50]

Re: which Octane is the best for a 1986 75 hp merc

I really think that with todays enthanol-mixed gas that it is best to run at least mid-grade fuel in them. Them meaning the older outboards. My '86 115 spark knocks like crazy with the factory timing running E10 87 octane. It runs great with 89 or higher. I get afraid of melting pistons with running it on low octane from the predetination. I can run 87 on my '04 60hp all day without worries though.

My opinion, run at least mid-grade for cheap insurance on the older motors.