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Far-I

Gasoline Question

32 posts in this topic

May be a dumb question but just want to clarify:

I got a new OB almost a week ago and, after considerable will power- will finally start breakin her in on friday. i want to pamper her with premo gas, but here is what the manual says

unleaded minimum pump posted 87 octane gasoline is recommended.

(Octane based on posted rating)

(91 based on the research octane method)

So this means 87 is recommended? or 87 minimum up to a 91 rating?

i know, dumb Q, but can't be too careful.

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Go ahead and use the 87.

The pump octane rating at U.S. pumps is an average of two lab-tested octane ratings, which includes the research octane number and a motor octane number. Look at the pump the next time you fill up and you’ll see the formula, (R+M)/2.

Other countries might only use the RON as a measure of octane, which will be listed on the pump as the advertised octane. Because of this, the rating on U.S. gas pumps is typically four to five points lower than other parts of the world

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but could a higher octane rating be better overall? or should i use only 87? i know i used 87 in my older 2 stroke because the higher octane gases hadn't been developed yet when the engine was manufactured, but a brand new one, higher octane may be better?

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Problem with where we live is that I have to buy 91 to get the non-oxy fuel. My 05 Merc calls for min of 87 but warns about using oxygenated gasoline. I'll bite the bullett and fork the extra few bucks to fill my boat with the good stuff. Alcohol has some nasty side effects on some rubber o rings, seals, and gaskets.

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I was told prem in all small engines, so thats what the boat gets.

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I go non-oxy on all small engines. If I could get non-oxy 87 oct. I would buy that but non-oxy is always 91 oct., at least that I've seen.

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Far I,

You are best off using the fuel that the manual calls for, regardless of opinions. In the "Good Old Days" before unleaded gasoline, octane ratings were generally higher and you could often buy 100 octane right at the pump. The fuel actually had additional lubricating qualities due to the tetraethyl lead used to raise the octane, but the tradeoff was toxic lead released into our environment. Buying "Premium" fuel nowdays gets you a little higher octane which actually slows down the burn rate of fuel, a property needed with higher compression motors, which todays outboards are not. An exception may be the supercharged Verados but I bet if you read the manual it will call for 87 octane. Premium fuel will NOT give you any performance increase.

The only possible exception might be to use the non-oxygenated premium fuel to avoid the ethanol content for older motors, say before the early '80's, but any motor built in the last 20 years has been designed to tolerate those fuels. Engine design must consider future warranty costs and if the seals had been specified with materials that were not tolerant of the ethanol, the manufacturer's warranty costs would skyrocket (money directly out of their pocket). Bottom line is that you should feel comfortable burning 87 octane pump gas in any engine that calls this out in the manual. The concept of using higher octane premium fuel for any reason is nonsense and simply a waste of your money. Do your homework, educate yourself and make the right decision.

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Yep good post Hydro.

The only reason to use premium fuel in a standard outboard is to stay away from ethanol. Remember though that not all premium is ethanol free.

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Straight from my manual:

"We do not recommend the use of gas which contins alcohol.

Gasoline containing alcohol may cause the following problems to you're outboard and fuel systems:

Corrosion of metal parts

deterioation of elastomers and plastic parts

wear and damage of internal engine parts

starting and operaitng difficulties

vapor lock or starvation

Some of these adverse effects are due to the tendency of gas containing alcohol to absorb moisture from the air, resulting in a phase of water and alcohol which seperates from the gasoline in the fuel tank.

The adverse effects of alchol are more severe with methanol and are worse with increasing content of alchol."

I'm more concerned with reformulated (oxygenated) fuel than with the octane rating itself. Like I said before, look at just more than just octane.

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I just read a blurb from a Yamaha engineer (NAFC Magazine). It basically said that you could run into issues running regular 10% ethanol gas in motors made prior to 1985. Anything newer and you should be fine.

I always run 87 octane. No sense spending more if the motor is designed to run on 87. Contrary to populare belief, 91 octane is not rocket fuel smile

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Contrary to populare belief, 91 octane is not rocket fuel smile

You're right, it's not. The higher the octane actually results in a slower, more controlled combustion.

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I recently purchased a bout with a 2000 Yamaha HPDI 150 and when I was in a dealership the other day the guy said to run 87. However, he also indicated that I should be adding a fuel stabilizer plus a Yamaha fuel additive (forget the name but it was like $40 and he said it would last 320 gallons). What are peoples thoughts on the fuel additives? He said it was due to the ethanol clogging things up.

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My manual also mentions some stuff like running addatives and a water seperator but the alternative is to run non-oxy fuel. I did the math and it's cheaper (and less to worry about) just to buy the non-oxy.

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I buy the "Ring-Free" additive for my 75 yamaha, my uncle had some issues and was told by the service guy that it helps prevent buildup on yammy 4 strokes.

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Use sea-from I've been running yamaha's for 20 yrs, never had a problem.

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it seems to me that i get more power, speed and quicker take off with oxgynated 87oct than preimum non oxy gas.. as for jhoson small motors before 1980 they have cork floats and the ethonal will eat those like a pig in a apple tree

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...the ethonal will eat those like a pig in a apple tree

LOL, that's funny smile

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I run non-oxy as well in a newer Optimax and have had no problems. I maybe a little overprotective with a fuel/water separator and run additives to it. I probably treat her better than anything else I have (including dog & wife!)

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it seems to me that i get more power, speed and quicker take off with oxgynated 87oct than preimum non oxy gas.

I've noticed the same thing. The lower octane burns much faster! I wish I had somewhere up here where I could get 87 non-oxy...best of both worlds.

Do you guys down by the cities have lower octane non-oxy???

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