Don, confirming your views on ethanol...

[MakingWaves]

S/N 3B368255
Don, from what I've found on this forum your opinion on ethanol is this: if your engine suggests to use 87 octane but you can find 89 octane with no ethanol you would rather use the 87 octane (with no more than 10% ethanol) but also use your cocktail of 1oz of Quickcare and 1 oz of Quickcleen per 5 gallons.

My Merc 250 xs 4 stroke before my current engine never saw ethanol but I was having to use 89 and up octane. If it's no longer an issue then I would rather use what Merc suggests. Thanks for any feedback. Steve

[Capt James]

I'm not Don, but I would only use ethanol free fuel. 89 octane ethanol free is NOT going to do anything detrimental to your 4 stroke 250hp Pro XS. 87 octane is the minimum octane required by Mercury for that motor and as the fuel sits in your tank and ages, it's losing octane.

[2dwoods]

I would think the cocktail is for 2stroke

[SilverFox579]

The fuel FAQ topic at top of this forum covers fuel recommendations. Fuel systems are designed to be safe with "up to 10% ethanol". Use 1oz each Quickare (or Quickstor if appropriate) and Quickleen to every 5 gals.

FWIW, my 14yr old Optimax has never had a fuel related issue, still has the factory black fuel line stub from the VST, and the same pulse pump it left Fond du Lac with. Every single minute of run time has been with top-tier fuel, less than 10% ethanol, 87 octane (correct for my engine) from a high traffic station and Don's recommended cocktail.

[EuropeanAM]

Since I don't think I've had to copy and repost this for May yet... we'll make this thread the "lucky one".

Your engine requires 87 octane fuel. It was built and CALIBRATED FOR 87 octane E-10. While it's acceptable to run higher octane, that is quite different from being "recommended or preferable".

FREQUENTLY ASKED QUESTIONS: FUEL AND FUEL ADDITIVES FOR 4 STROKES

Fuel Selection:

Make your fuel selections based on the following criteria, IN THE FOLLOWING ORDER:

-High Traffic, Top-Tier (Name Brand) Fuel
-Appropriate Octane Rating (see above info)
-Lowest possible ethanol content (NEVER to exceed 10%).
-While it may be preferable to utilize a fuel that contains lower (or no) ethanol, use of fuels that are SUBSTANTIALLY higher octane can result in decreased performance, decreased fuel economy, and potential for carbon buildup. Higher octane fuels burn SLOWER and COOLER.

[MakingWaves]

Thanks for your patience. I felt I needed to qualify especially the "cocktail" portion of the question since that was posted 4 years ago.

[EuropeanAM]

FAQ material is only updated when there's a CHANGE or ADDITIONAL information.

[MakingWaves]

FAQ material is only updated when there's a CHANGE or ADDITIONAL information.

Gotcha, thx.

[Woody b]

Automotive technician here. The misconceptions about ethanol amaze me. Some engines, and some fuel system components weren't compatible when ethanol was first added to gas. Ethanol isn't the devil many people make it out to be. With the exception of incompatible fuel system components from years ago most, or maybe even all of the problem blamed on ethanol are caused by sitting. My professional opinion is, if you have a car, truck, boat, piece of power equipment ect that's going to sit quite a bit use ethanol free fuel. Fuel stabilizer can help but if you aren't going to use the entire tanks fuel capacity in a month or less I'd recommend ethanol free, and fuel stabilizer. If you're going through a tank or more a month simply use a good brand top tier fuel. (Don mentioned top tier too) https://www.toptiergas.com/

Ethanol is hygroscopic. It will readily absorb moisture. That's not a problem with a little bit, but over time it can absorb so much moisture it will separate.

[unknown angler]

Yes the engines run just fine on 10% ethanol fuel, but it's the sitting in the tank in the humid summers if you can't get on the water that concerns me.

[Kodiak16]

Yes the engines run just fine on 10% ethanol fuel, but it's the sitting in the tank in the humid summers if you can't get on the water that concerns me.

Fuel system is pressurized. Where would the moisture enter?

[unknown angler]

My 1999 boat tank is vented to the outside atmosphere.

[EuropeanAM]

Fuel system is pressurized. Where would the moisture enter?

Actually not accurate. They must hold up to 5 psi of pressure. They also must vent to permit air to enter as fuel is depleted (inward venting is good, outward venting not so good per EPA).

So some atmospheric moisture can potentially migrate to the system during natural venting.

[Pathfinder2200v]

Always great info here to learn from, especially what Don shares!

Since the early 2000’s I’ve exclusively run Rec90 in a variety of outboards w/ different additives and continued using Rec90 after I re-powered with a 2020 200hp Fourstroke. Gonna force myself to start using a quality 87 only, and of course continue using Don’s cocktail. Curious to see if there any difference in performance.

[bbqpitboss]

So the use of “real gas 87 octane” is not recommended and can hurt performance? I ask because I pick up my new boat tomorrow.

[Squire]

I have a 2017 Mercury Optimax 250 2-stroke. Marina only has 90 octane ethanol free gas. I used it for first year or so and had carbon build up issues even with the recommended fuel treatments. I now trailer down to a busy gas station and get the 87 with 10% that has the sticker that indicates the gas has all the appropriate
additives. Now my prop and the exhaust are clean with no build up, boat doesn't develop a miss, etc. lesson learned, octane does make a difference.

[bassfisher444]

So the use of “real gas 87 octane” is not recommended and can hurt performance? I ask because I pick up my new boat tomorrow.

No, where did you see that?

[EuropeanAM]

So the use of “real gas 87 octane” is not recommended and can hurt performance? I ask because I pick up my new boat tomorrow.

Please re-read. That's exactly the opposite of what is being communicated.

[bbqpitboss]

My bad Don, I re read the above and get what you are saying now. Lowest ethanol content (which includes 0 percent) Just don’t go crazy on the octane. Do you recommend the same cocktail?

[JS!]

I re read the above and get what you are saying now. Lowest ethanol content (which includes 0 percent) Just don’t go crazy on the octane. Do you recommend the same cocktail?

THIS LINK was posted in Post #5 and links you to the FULL “FUEL & FUEL ADDITIVES FOR 4-STROKE MODELS” FAQ post which is, per Don, still current and applicable. IF you didn’t click on the link above in post #5, I can see where ONLY reading this thread might not answer all of your questions. Hope that helps!