1976 Mercruiser 233 Fuel Type

[neno74]

Hi,

I have searched this forum and the internet and learned a bit but perhaps someone with the same motor will have actual experience with this. I have a 1976 Mercruiser 233 (Ford 351) with a 2bbl carb I/O setup in my boat. It is the original engine in the boat and is completely stock configutation except that I upgraded the ignition to a Pertronix electronic ignition along with all the typical maintainace stuff like rebuilt carb etc. The label on the valve cover states that the fuel recommended is 91 Research Octane or higher. For many years I always used Mid Grade pump gas 89 octane or Premium 93 ocante on this boat without any issues. Well with the gas prices these days, filling a 70 gallon gas tank is a big financial deal. Is 87 octane pump gas sufficient for this engine? I have read that "Reasearch Octane" also known as RON is numerically higher than the USA standard number that is an average of 2 different measurements (R+M/2). Why Mercruiser used the RON decal at that time is confusing. I also realize that gas back in the 1970's was all gas without Ethanol. These days all the gas station I know of have 10% ethanol in the fuel. Does this affect Octane?

Anyway, will 87 octane work for my Mercruiser 233 without any issues? Thanks for your time!

Neno

 

[Bondo]

I also realize that gas back in the 1970's was all gas without Ethanol. These days all the gas station I know of have 10% ethanol in the fuel.

Ayuh,....... It'll burn whatever gas ya dump into the tank,......
If yer that worried 'bout it, cut the timin' back abit, 'n fatten the fuel slightly,....
That'll keep detonation at bay,.....

The problem will be the ethanol, as it rots some ole fuel lines, gaskets, connection, etc,......

'round here, we can buy ethanol-free, I think it's rated 93,....
With a diesel truck, all the gas I buy is such, as it's all for various toys, 'n tools,.....
It don't turn rotten nearly as quick,......

 

[Scott Danforth]

91 RON octane is close to 85 R+M/2 (current pump swill)

I would simply use 87 - 89 octane rec gas

corrected the scale conversion

 

[achris]

.... Why Mercruiser used the RON decal at that time is confusing...

Because the rest of the world used (and still uses) RON. It's only in 'murica that R+M/2 is used. Same as you're still using imperial. The rest of the world has moved on....

Chris...

 

[Scott Danforth]

Because the rest of the world used (and still uses) RON. It's only in 'murica that R+M/2 is used. Same as you're still using imperial. The rest of the world has moved on....

Chris...

˙ᄅ/(W+ɹ) sɐ sdɯnd uo uǝʇʇᴉɹʍ uǝʇɟo puɐ '(Iʞ∀) xǝpuI ʞɔouʞ-ᴉʇu∀ ǝɥʇ pǝllɐɔ 'NOW ǝɥʇ puɐ NOɹ ǝɥʇ ɟo ǝƃɐɹǝʌɐ ɹo uɐǝɯ ǝldɯᴉs ǝɥʇ sᴉ ɹǝqɯnu ǝuᴉlpɐǝɥ ǝɥʇ 'sǝᴉɹʇunoɔ ɹǝɥʇo ǝɯos puɐ 'lᴉzɐɹq 'sǝʇɐʇS pǝʇᴉu∩ ǝɥʇ 'ɐpɐuɐƆ uᴉ ʇnq 'NOɹ ǝɥʇ sᴉ dɯnd ǝɥʇ uo uʍoɥs ƃuᴉʇɐɹ ǝuɐʇɔo ,,ǝuᴉlpɐǝɥ,, ǝɥʇ (puɐlɐǝZ ʍǝN puɐ uɐʇsᴉʞɐԀ 'ɐᴉlɐɹʇsn∀ uᴉ oslɐ) ǝdoɹnƎ uᴉ sǝᴉɹʇunoɔ ʇsoɯ uᴉ

 

[neno74]

I did upgrade all the hoses (fuel filler and fuel pump supply to modern marine grade hose) that is ethonal compatible. The carb was also rebuilt using ethanol compatible gaskets and parts. I do replace the fuel and water seperater filter yearly. My one concern is the aluminum tank and hope that the ethanol doesn't cause corrosion issues there.

I know from road trips over the years, fuel octane ratings differ in different states. I have seen the regular grade gas octane rating from as low as 85 up to 89 depending on where in the USA I was. Where I am located (Chicago) and the surrounding midwest states, the regular grade gas is 87. I don't understand why there is such a drastic difference in octane rating per state.

Lastly, at $5 gallon for the cheap stuff and premium going for well over $6, I am going to try 87 this season. Keeping my fingers crossed that I don't have any detonation issues. Thanks again for you replies!

 

[Scott Danforth]

I am going to try 87 this season. Keeping my fingers crossed that I don't have any detonation issues. Thanks again for you replies!

if you are concerned, back your timing off by 2 degrees, however you should be fine

 

[achris]

... I don't understand why there is such a drastic difference in octane rating per state..

I thought it was all one country. Don't you have a 'national fuel standard', like most other developed countries?

 

[dingbat]

Don't you have a 'national fuel standard', like most other developed countries?

No......The federal Clean Air Act establishes national fuel emission standards, but allows states to adopt unique fuel programs to meet the need for sufficient flexibility to address air quality issues at the state or local level.

 

[neno74]

Interesting that fuel stadards are left up to the states. So is Octane added at the station or at the depot where the tankers pick up the fuel? I always wondered how some gas stations have 4 or 5 different fuel options at the pump yet you really only see 1 tanker delivering the fuel to the station.

 

[achris]

1 tanker can deliver many different fuels. The tanks are compartmentalized. Next time you see one, look at how many delivery hoses it has. Each hose is for a different fuel.

 

[Scott Danforth]

1 tanker can deliver many different fuels. The tanks are compartmentalized. Next time you see one, look at how many delivery hoses it has. Each hose is for a different fuel.

dont forget the blend pumps at each station. low grade and premium are mixed for midgrade. most tankers have 5-8 fuel tanks on board

E0 (87-89 octane rec gas)
E10 low grade (87 octane in most states)
E10 premium (93 octane in most states)
E85
Diesel

things like E15 are usually a blend of E85 and E10

however there is no standard for the coutry. there is however local and state government taxes. and there are states that sell 85 octane (when they shouldnt.... such as the mountain area Idaho, etc.).. try driving up a mountain in a rented suburban on 85 octane. I think the pistons had holes in them by the time I went over the summit as the thing was pinging all the way up

however back to the Topic.

the OP will be fine with 87 octane E10