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[Spawn Sack]

Somewhat lame topic...but what the hell

New (to me) motor is 2011 Merc 90/65 jet. 2 stroke. Never thought to ask original owner what grade of gas he used.

Manual say min 87. I'm inclined to just run 87. However talking to boat guys at work several say the use/reccomend 91 or 94.

My dad who has a 175 merc sportjet in his jet boat only runs 94. Says his motor starts and runs better on it.

Is it all in their head???

IMO motors that say min 87 typiclaly run FINE on 87. For example my chainsaw, quad, 4 stroke 5hp outboard and so on all run fine on 87. That being said I have never tried higher octane fuel in any of them. Perhaps they would run better and  I don't know cuz I never tried?

[Damien]

The bigger thing is to make sure you use gas that is ethonol free.  Higher octane usually contains less ethonol, that is why the motors seem to run better.

Its not the octane necessarily.  Google ethonol and outboards....its scary.

Ethanol is hygroscopic, meaning it has a strong attraction to moisture. Ethanol increases the amount of water accumulating in fuel tanks. Ethanol produces less energy (BTUs) than an equivalent unit of gasoline. Ethanol fuel’s usable life span may be less than the normal length of off-season boat storage.

One of the biggest reasons why ethanol fuel and boats don’t go together is that ethanol has the unhappy ability to attract water. And as almost everyone knows, water in gas engines is a serious problem.

Be sure to have a high-quality (25-micron minimum) marine fuel-water separator (filter) installed in the gas line, and check it and replace it often. This filter prevents not only water from getting to the engine, but also debris that may result from ethanol degrading a boat fuel tank and gas lines.

And here is a handy list, I just go to Costco for my boat gas;
http://pure-gas.org/index.jsp?stateprov=BC

[Dr. Backlash]

For the last few years the jets in my carb on my 1999 15hp Merc 4 stroke kept getting clogged after barely using it.  I kept having to take apart the carb and clean it thoroughly every year until last year when I called Mercury and asked them why my carb kept clogging up and they said it was the ethanol in the gasoline, and they suggested that I switch from 87 octane to ethanol free gas - most Shell stations their 91 octane is ethanol free.  Even though its recommended to use 87 octane on my motor, the Merc guys said to use higher octane that is ethanol free and to make sure to use the Mercury fuel treatment stuff every time I fill up the tank. Ever since I switched to higher octane ethanol free gasoline my carb has ran perfectly. Its crazy the damage that ethanol does to carbs! (its even crazier that we're using corn (food) to make gas)

[BNF861]

The bigger thing is to make sure you use gas that is ethonol free.

Exactly.

In a marine motor, ethanol free is more important than high octane. I doubt that you could feel a difference in your boat between running 87octane and higher.

The catch is, ethanol free gasoline is usually only offered in some brands highest octane so you need to buy high octane to get what you need.

[Spawn Sack]

Interesting! Thanks guys for the info.

I could be wrong, but I thought all Costco gas says "may contain up to 10% ethanol," including their 91. I know for sure the Chevron 94 says "contains no ethanol."

If I'm going to Abby (live in Chilliwack) I will try and bring a couple of 20L jerry cans for the boat and hit up Costco (assuming their 91 is e/free).

Now this is probably a dumb question...but why is ethanol so important in marine motors? Yes I realize the motor always runs in water, but I didn't think the water cooling the motor and falling from the sky would get into the fuel. Does it? How?

I use my chain saw and quad in wet/moist environments and just run 87 in both of them. But I guess the quad is 4 stroke EFI. Would ya'll run ethanol free gas in you chainsaw too?

[TheFishingLad]

Ethanol is important to keep out of your fuel, because ethanol is hygroscopic. Little more detail (sort of) than stated above is the humidity in the air is enough to saturate the ethanol to it's max level fairly quickly, which means the moisture it draws in can no longer be absorbed, which leads to fuel separating into the gas. Now, this isn't an issue if you use a lot of fuel and use it often, but when sitting it can be problematic.

This also rings true with your vehicles brake fluid and coolant, as both of those fluids are hygroscopic and will absorb it's max amount of moisture (roughly 4%) in about 2 years on the coast. Any excess moisture will pool in your master cylinder, and worse yet in your ABS pump or calipers. As for coolant the boiling point will go down and can cause issues (though not really seen in warmer temps)

[DanL]

And here is a handy list, I just go to Costco for my boat gas;
http://pure-gas.org/index.jsp?stateprov=BC

Interesting, I didnt know any automotive gas was available nowadays ethanol free. I recently picked up a used aluminum that came with a 90's era's Yamaha 2-stroke. The previous owner said he just used regular 87 octane and the motor was a little tough to start up after sitting since last season. He had been using 50:1, presumably with no stabilizer, while the sticker on the motor said 100:1 so I just chalked it up to the old gas but now I wonder if the ethanol content could have been a factor too...

I haven't had a chance to take it out yet, but will definitely chuck out the old gas and mix up some new ethanol free fuel with the lowest octane rating I can find, which based on the above link looks like will be 91.

On a related note, any suggestions on how to dispose of 10 litres of year-old 50:1 mix?

[Zackattack]

Its brutal. Only a few years ago I only had to watch out for ethanol at budget gas stations and Husky I think, but now I think its even in Chevron unless its 94...
Well at least it says it "may contain"
Corn is in everything nowadays! Horrible!

[TheFishingLad]

I had a thought after I posted last night. An argument where one would want ethanol in their fuel, especially if moisture is an issue.

With our humidity, moisture will be in the fuel no matter what. Now if you had fuel with ethanol, this would be no problem as it would absorb it, and get burnt off harmlessly, but without ethanol, it does not get absorbed and can create a later on the fuel, which can be put through the engine in a more harmful way.  I would say ones bestb bet is a good water fuel seperate and check often.

[Dr. Backlash]

Most Shell gas stations have 91 octane that is ethanol free. Might save you trips to a bunch of different gas stations - just go to a Shell and see for yourself

[BNF861]

Although there are some exceptions at other stations, from what I have seen Shell 91 and Chevron 94 are both ethanol free.

Most stations and grades will say may contain ethanol and generally if it says may they mean it does.

[TacoChris]

Engines are designed to run at the Octane level indicated by the manufacturer. My understanding is the science does not support running higher Octane in these engines. However ethanol does use more fuel to produce the same power. 3 to 4% by US government estimates.   Older engines may benefit as there is concern ethanol may be corrosive for some components. Newer engines should be designed to deal with it.

Most peoples vehicles see more moisture than many boats or outboard motors ever do. My outboard is stored in my garage most of the time.

[Spawn Sack]

All good input, thanks guys. I am thinking of implementing the following:

For now, just run ethanol free gas in the boat. Costco or Shell 91, or Chevron 94.

When I have some extra cash, buy a fuel/water seperator/filter and install in main gas line. We are more or less tapped out cash wise on the boat after purchase price, and the TAX. Plus we need to get a proper anchor/bow roller for the Fraser, plus we have a fish finder that may or may not be usable depending how my next round of trouble shooting goes

Any know about how much these fuel/water seperators go for? Merc has one that looks decent:

https://www.mercurymarine.com/en/ca/parts-and-accessories/mercury-marine-products/fuel-care/fuel-care/

I like the looks of this one better as you can drain the water out without having to remove/unscrew the filter.

http://www.westmarine.com/buy/racor--replacement-gas-filter-water-separators-for-mercury-mercruiser-engines--P000411462

Just another thought....

Do you think one would be okay to ONLY run ethanol free gas and not bother with the fuel/water seperator/filter? In other words, does/can ethanol free gas have issues with moisture? There is a fuel filter in the fuel line near the motor. Would it be overkill to run the extra filter and the ethanol free gas?

[TheFishingLad]

I feel we can be getting into superstition area now, and personal preference. I'm an overkill guy, and enjoy the ease of unscrewing a t-bar to drain the water like on some diesels. The fuel filter itself will just be for particles, and the filter material itself won't be fine enough to trap water.

I reckon 87 Octane (or manufacturer's recommended), water separator, and new fuel when you know it'll be sitting for extended periods and you'll be gravy.


Side note: I am not an outboard guy, and am just applying my automotive schooling here.

[skaha]

--funny when we had regular fuel...everyone reccomending adding ethonol... to stop freeze up and reduce condensation .

--I use higher octane in modern 90 4 stroke and always put stabil type product in it as I only go through a few tanks of gas a year. Old boat 85 used to burn 45 gallons in a weekend.

--All Voodooo to me.. I use petrocan because it is the closest station. Cheveron and Shell are in town and the highest prices in the land.

--I think sometimes you just get a cranky engine that only seems to want to run on a particular brand.
--My engine is a 2006 have had no problems.

--Older engines I can see a problem... I was so happy when I got my new engine fuel injected.
--