gas octane

chuck-p · Sep 2, 2005

I have a 1974 lark 50, my owner's manual says to run a minimum octane rating of 94 but after reading many posts on iboats everyone seems to recomend 87. Should I continue to run premium or is 87 ok.

JB · Sep 2, 2005

Re: gas octane

That was 31 years ago, Gonfishin. 87 is the stuff to use in 2005. Good luck.

oldboat1 · Sep 2, 2005

Re: gas octane

Has it really been 31 years? I think it matters whether the gas is fresh, but octane isn't so critical. Having said that, I just bought a couple of gallons of premium for use in testing out a motor I want to get running -- at $3.79/gal. Regular was 30 cents cheaper, but at that price 30 cents just didn't look like much more.

chuck-p · Sep 2, 2005

Re: gas octane

thanks for the quick replie guys i am going to start using 87 and save a few bucks.

Pony · Sep 2, 2005

Re: gas octane

i thought the combustion temps on the higher octanes was too high for outboards....in that they leave higher amounts of residual carbon etc. which i believe is why most people here recoment the 87octane. om sure someone can back me up on that.

djzyla1980 · Sep 3, 2005

Re: gas octane

87 is what a mechanic at one of the shops here told me... for the same reasons pony... However.... here it costs more to run the 87 then the 93 or 94.... by about 25 cents So keep saving money so I can spend more

itstippy · Sep 4, 2005

Re: gas octane

That's the first I've heard of OMC recommending anything other than 87 Octane. The owner's manual says "minimim" of 94!? What's the scoop on that, you experienced ones? Part of the unleaded fuel panic of the early 1970's? Dave, you get 94 octane for 25 cents cheaper than 87 octane? Around here they call 94 octane "premium" and charge an extra 40 cents per gallon. It's all my old Honda car will burn, so I bite the bullet and pay the price. "Old Blue" knocks & pings & diesels with "regular" gas (87 octane). At 233,000 miles I just buy the premium fuel - I'm not about to mess with the motor! But I run fresh 87 octane in all my outboards.

chuck-p · Sep 5, 2005

Re: gas octane

Here is a quote from my owners manual "RECOMMENED GASOLINE Use a Regular leaded gasoline or a Premium leaded gasoline that has a minimum octane rating of 94 (Research Number). NOTE: If recommended gasoline is not available when operating in any other country than the United States, Canada, or Australia, see your DEALER." Evinrude 1974 ownener's manual 50HP Lark Models 50472 50473 Sizzler Models 50442 50443

chuck-p · Sep 5, 2005

Re: gas octane

Where the 1974 50hp's a higher commpresion motor, or has gas changed that much in the last 31 years.

djzyla1980 · Sep 5, 2005

Re: gas octane

Yeah... it pisses me off everytime I see it. the 94 has ethenol... so I believe it's there way of getting us to buy "clean" burning fuel. I don't ask I just buy. maybe were just half a$$ backwards here but it's that way at all the stations I've been to. Go about 100 miles south and it's the way it should be.... Who knows My manual actually states 94 octane for my motor. But that was in 70's so I'll stick to what the pro's say and pay the extra for cheap gas....lol

Paul Moir · Sep 5, 2005

Re: gas octane

Research number (AKA RON) is a different rating system than used in the US/Canada, where we use Pump Octane numbers ((MON (motor octane number) + RON) / 2). 94 would generally be about equal to 89.

chuck-p · Sep 5, 2005

Re: gas octane

Thanks Paul that clears up my questions about octane and wich gas to run.

Paul Moir · Sep 5, 2005

Re: gas octane

I would stick with 87 myself, as JB said. After all, how many posts do you see here from people with predetenation damage caused by too low an octane fuel? Verses the numbers you see with coked up rings? Up here, I run into other problems when using high-octane fuels. Rubber parts dissolving, platic parts cracking, etc.

gas octane

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