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Fuel Octane amp Life

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rude70

Contributing Member
"I have 1977 70HP. I live in A

"I have 1977 70HP. I live in Australia where standard unleaded fuel is 91 octane,95 & 98 is also avaliable (as is ethonal based fuels). What octane rating should I run and how long does fuel laast before it goes stale/off?

Thanks"
 
"Use the lowest octane availab

"Use the lowest octane available, not to drop under a octane rating of 87. Gasoline has been know to sit for a couple years before going stale. Stale gasoline cannot be mistaken.... a odor that will make a drunken shunk head for the hills.

Thousands of parts in my remaining stock. Not able to list them all. Let me know what you need and I'll look it up for you. Visit my eBay store at:

http://stores.ebay.com/Evinrude-Johnson-Outboard-Parts-etc?refid=store"
 
Thanks Joe. A dealer had advus

Thanks Joe. A dealer had advused me to use 98 octane! I have just rebuilt the power head so upon your advice I will use 91 octane. Why do you recommend to use lower octane fuel?

Thanks
 
"Well, Australia has a differe

"Well, Australia has a different octane rating system as the US. You guys use straight RON rating, whereas US is an average of RON & MON. No big deal though, it just works out that your 91 is our 87, 95 to 89, etc. Anyway, it is advised here (as stated on Evinrude's website) that 87 is fine, but 89 is recommended. So, I'm sure you'll be fine w/ 91, but 95 won't hurt and might actually be a little better. 98 is just a waste of money though."
 
"Q - What grade of fuel should

"Q - What grade of fuel should I use in my motor?

A - Current recommendations are to use a minimum of 87 octane, 89 octane is preferred. There is no additional benefit from using higher-octane fuels, in fact they may cause hard starting conditions in hot weather. If you have an older motor and the owner's manual requires premium fuel, here's why:

When these were built, the best oil available was TCW-2 rated, and did not contain the additive package (detergents, carbon preservatives, etc.) which our current oils (XD-30, XD-50 and XD-100) contain today. In that era, premium fuel contained the additive package that helped prevent the formation of internal engine deposits. That's why premium fuels were preferred at the time. Ultimately, in the late 90's the federal government mandated fuel refiners to use the same additive package in all grades of fuel and the premium fuel requirement was dropped"
 
"Outboard manufactures design

"Outboard manufactures design their engines around the fuel available at the time and i have seen over the years the compression pressures slowly drop from the 1970's to now. The octane rating of the fuel is it resistance to knocking or detonation. If this 70hp has been rebuilt a few times in its life which here in Australia is a possibility the compression ratio could be higher than what it was when new.

Fuel is oxidising from the moment its sitting in your fuel tank, fuel also loses 1 octane number per 20 deg C so if you couple all of these factors together your engine could be on the borderline with the min octane rating."
 
"the more I here of these octa

"the more I here of these octane ratings the more confused I get. I alway get "chicken" and opt for premium.
Hold my hand one more time...please. My '75, 115 has never overhauled or even heads removed. Can I use the 10% ethanol in 87 octane? I decarbon in once a year with either the OMC spary down the throat stuff or the Sea Foam procedure."
 
In Oz ethanol blends of upto 1

In Oz ethanol blends of upto 10% are allowed an are becoming popular. The octane rating is 94/95. Any views on using ethanol ased fuel since it is the same price as 91 octane? Thanks
 
""the more I here of these

""the more I here of these octane ratings the more confused I get"

You need to get your head around the fact that most countries including the UK and Oz use the RON scale of octane rating while North America and a few other countries use a different scale. It is all explained in Wikipedia

Use 91 octane fuel in Oz, UK and other countries ussing the RON system. Use 87 octane in USA Canada and other countries using the Anti knock Index, Road Octane Number or Pump octane number system
Ethanol blends up to 10% are acceptable but some hoses etc may not be suitable for it."
 
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