gas grade

[Johnson110]

helllo, i have an 1986 omc crossflow 110 hp, mechanic said to use 89 octane, would it be ok to use 87 octane useing mercury premium plus oil, just do not want to ruin engine on 87, is there really a diffrence on this size outbord for the octane rating, i mean any benefit to using 89 octane? thanks for your replys, ps: great board sound advice guys thanks

 

[rickdb1boat]

Re: gas grade

87 would be best... And no benefit to using 89 octane..

 

[WillyBWright]

Re: gas grade

Octane is good, alcohol is bad. Most gas above 87 octane uses ethanol to boost the octane. Gas and oil mix, gas and alcohol mix, alcohol and water mix. But oil doesn't mix with alcohol and water. So if there's water in the tank, it'll settle to the bottom along with proportional amounts of alcohol and gas. But there won't be any oil there. No oil, no lubrication. Result...scuff and sieze. Even if you have VRO, the no-oil mix settles to the bottom of the carb and the result is the same. That's the main reason not to use higher octane fuels in a 2-stroke.

 

[rickdb1boat]

Re: gas grade

The main reason not to use higher octane is that it burns cooler and can carbon up your motor..

 

[jim dozier]

Re: gas grade

WillyBWright I would take issue with the statement that most gas uses alcohol to achieve higher octane. If you replace the word "most" with "some" I'll agree. More often than not, other aromatic hydrocarbons are used (and are superior) to raise octane. Also higher octane is not "good" if the engine does not require it and can be a waste of money. Much of the use of alcohol is politically driven and may be in greater use in some states (Midwest grain producers). Here in Florida the law requires that a sign be posted on the pump if alcohol is used.<br /><br />Use the lowest octane that is appropriate for the engine. In virtually all 2-stroke outboards that would be 87 octane in USA standard =<br />(R + M)/2 which is the average of 2 different methods; R (Research method) and M (Motor Octane Method) for calculating octane. Overseas octane numbers are based on a different calculation.

 

[Johnson110]

Re: gas grade

thanks for your reply i will go with 87 octane!