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[Spawn Sack]

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.

I would be inclined to agree with you. For now I think I'll just run ethanol free gas and after we get some higher priority stuf sorted out on the boat, down the road I'll look at the fuel/water seperator filter. Only thing I don't really like about them is they need to be installed on the main fuel line somewhere, and most likely in a vertical position to work properly. Would want it somewhere where it couldn't easily take an impact (someone slips or whatever) and busted open/apart. Would have to take some time and think where it could go to be as out of the way as possible. Ideally under the floor but I doubt one would fit there.

[skaha]

I would be inclined to agree with you. For now I think I'll just run ethanol free gas and after we get some higher priority stuf sorted out on the boat, down the road I'll look at the fuel/water seperator filter. Only thing I don't really like about them is they need to be installed on the main fuel line somewhere, and most likely in a vertical position to work properly. Would want it somewhere where it couldn't easily take an impact (someone slips or whatever) and busted open/apart. Would have to take some time and think where it could go to be as out of the way as possible. Ideally under the floor but I doubt one would fit there.

--I have a removeable box around my filter and of course an in line shut off valve as I run line to both main and kicker through the filter. Agree a lot of connections where things can go wrong even if checked and maintained.

[DanL]

At least in the LML, it appears marinas all seem to have mid-grade 89 ethanol free fuel. I assume there's no issues with those marina fuel docks, like stale gas etc?

[Spawn Sack]

I'm not entirely sure as I've never fueled up at a marina. I'll be primarily hitting up the fraser adn connecting rivers and a bit of lake trolling so for me it'll be Chevron, Shell, etc.

Plan is still to burn ethanol free gas whenever possible, and down the road the road if the logistics/location looks good for a fuel/water seperator filter to install one of those then probably step it down to 87.

Thanks for all the input guys appreciate it.

[juno]

 I bought a slightly used 4 stroke 75 merc 2years ago   at a marine shop   they told me all it needs is regular, but I must agree with the ethanol issue, it traps water

[bigblockfox]

i would stick to the costco 91. at the Langley costco you can usually get 91 for a couple cents more than regular at other gas stations. maybe the abbotsford costco is even cheaper because the transit tax dosent apply. i put it in 50hp jet and in one of my mustangs.

[andrewscag]

Another issue with ethanol is its tendency to degrade some non metal bits on older engines.  Newer ones are built to take it but this can be another source of problems for the older two strokes.

[Sr SQ]

Another issue with ethanol is its tendency to degrade some non metal bits on older engines.  Newer ones are built to take it but this can be another source of problems for the older two strokes.

Bingo…….on top of the H2O absorption and phasing issues with Ethanol it will destroy older rubber seals and lines, newer motors have neoprene rubber seals and lines to combat the alcohol.
Its evil stuff in an older engines especially in marine applications, lots of documented evidence of this, just read your mfg recommendations.
Just because some have been lucky saying its ok is the same as saying the old polly-B plumbing was ok.

As for the original post about octane……
Running higher octane than recommended will increase the temperature in the cyl head and pistons……….period.
Too much octane will be a problem in any motor however, how much is too much is dependant on engine and load.

Personally I would run ( and do on my own engines that burn gas)  the 94 non ethanol and monitor plugs to ensure temps are in check.

[canso]

As for the original post about octane……
Running higher octane than recommended will increase the temperature in the cyl head and pistons……….period.
Too much octane will be a problem in any motor however, how much is too much is dependant on engine and load.

Personally I would run ( and do on my own engines that burn gas)  the 94 non ethanol and monitor plugs to ensure temps are in check.

 that's a myth
 low octane can cause higher combustion temps. do to pre ignition and detonation. If you don't have those problems the only thing high octane will do is drain your wallet.

Montoring your plugs is checking for air/fuel mixture and maybe some oil. Too much air runs hot, too much fuel runs cold. Your plugs won't tell you your octane is too high or low.

[Spawn Sack]

Interesting comments by Sr SQ and Canso. The manual says "minimum 87" but does not say anything about "do not exceed XX octane." I am by no means a mechanic but for what I have heard over the years burning gas higher in ocatne than needed will not harm the motor but if not needed is just wasting $. For example our 4Runner runs fine on 87 and is made to run 87. So we use 87. My car has a tightly wound DOHC motor and calls for min 91. I always run 91 as the motor sounds a bit growly and underpowered on regualr gas.

Any opiniuons on "best" fuel/water filter?

Looks like the Mercury one you can not drain just the water out. You need to replace the whole filter like an oil filter. I have seen other brands online (Raycor?) where you can drain just the water if you want from a clear bowl at the bottom of the filter. Seems like being able to SEE if any water is being drained from the fuel and being able to remove it is a good feature.

[RainbowMan]

I went cheap and used regular 87 in my Honda 4-strk for the entire season last year and winterized my boat with some fuel stabilizer in the winter. It was a BAD decision 
Motor gave my all sorts of grief this spring to the point that I had to call Honda for help. Service manager told me 'never put gas with ethanol in a built-in fuel tank. In a portable tank, always drain gas at the end of season b/c ethanol+plastic = trouble. Always use Shell 91 or Chevron 94 and add some Seafoam to it'. That recipe saved me a lot of $$$ because it removed the trapped water from the carb and also burnt the gunk and cra* from the fuel line. After a few trips, motor is now back to its normal and isn't acting up anymore.

[ShaunO]

Guys,

I work with fuel, a lot.  I work with the CSA on producing fuel handling specifications, and I regularly deal with CAN/CGSB standards on fuels.  If you don't know what those are, please look them up.

This thread has a number of partial truths and some complete falsities.  Let me try and clear the air as quickly as I can.

• Ethanol adds octane to gasoline.
• Ethanol is a hydrophilic, meaning it likes water. 
• Gasoline is hydrophobic meaning is does not like water. 
• Gasoline can be blended with ethanol to achieve the advertised octane rating (remember this!) but also makes it able to absorb more water. 

Gasoline is produced to a specific standard and it is very, very dry.  Dry fuels, amongst other things, have a tendency to absorb moisture from the atmosphere.  Gas tanks "breathe" with changes in temperature and the fuel volumes expand and contract with the heating and cooling cycle.  This process brings in fresh, moist air.

Unblended gasoline can already hold dissolved water, but when blended with ethanol the ability to hold water is increased.  At a certain level of saturation, ethanol blended fuels can hold no more water, and the ethanol/water mixture will literally drop out of suspension (phase separation) to the bottom of the tank.  This leaves you with a corrosive cocktail at the bottom of your tank and decreased octane gasoline floating above it.  This is bad. The fuel pickups are also on the bottom of your tanks meaning that this mixture will undoubtedly be ingested by your engines.

So, in summary.  Ethanol blended fuels are FINE as long as you are not storing them for ANY LENGTH OF TIME!  Storing ethanol blended fuel in a moisture rich environment is inviting problems.  That said, some heavy users believe the use of ethanol blended fuels is actually a good thing in boats that are regularly used as it can hold more dissolved water resulting in less free water at the bottom of their fuel tanks.  For most of us weekend warriors ethanol blended fuels are going to sit, tank vents open, absorbing moisture from the air, creating problems.

If you're a weekend warrior like me, pay a bit more at the pump and avoid ethanol blended fuels.  An ounce of prevention is worth a pound of cure, right?

Points for consideration:

Q. Fuel stabilizer will prevent the absorption of water into fuel
A. No. Fuel stabilizers are used to prevent the chemical decomposition of gasoline into an unusable state.  It cannot change the actual properties of the fuel.

Q: Higher octane fuels burn hotter
A: No, they do not.  In fact higher octane fuels burn slower when combusted.  Octane is a measurement of a fuels resistance to detonation or knock, not its MJ/kg (in short terms, energy). This is important in higher compression engines like the example above.

Q: Fuel filters will remove all water from fuel
A: Most water can be caught by an inline fuel filter in addition to particulates.  I recommend the Racor line of inline spin on fuel filters from Parker. The ones with the reusable clear bowls allow you to see if there is water being picked up from your tank.  Most retail fuel dispenser have 10 micron filters in them, so the use of 10 micron is what I would personally use.

I hope this helps clear the air about octane and ethanol blended fuel.

Cheers,

Shaun

[Wiseguy]

Great post. I always use premium fuel ( highest octane ) in my out boards and a fuel stabilizer when storing fuel over the winter months.

[RainbowMan]

Excellent post, Shaun. Thank you.

[Spawn Sack]

Awesome Shaun! Can't thank you enough for that info.

When I have a chance I will buy and install a fuel/water seperator filter (probably the Racor). In the mean time, I will use ethanol free fuel as I don't run the boat more than once a week or so, and over the winter it will sit for several months in the tank.