If memory serves me seems like most n-ethanol gas is 89. I have a 2012 115 optimax so I would think it is the best choice.
If memory serves me seems like most n-ethanol gas is 89. I have a 2012 115 optimax so I would think it is the best choice.
By me its either 87 or 91. I've seen Rec90 on the coast but don't ever recall seeing 89.
No.
You are flipping the "Fuel Selection Criteria" upside down.
Make your selections based on the following criteria, IN THE FOLLOWING ORDER:
1. High Traffic, Top-Tier, NAME BRAND fuel.
2. Correct octane rating for your engine (87 OCTANE)
3. The lowest possible ethanol content available IN THE ABOVE CRITERIA (up to 10% ethanol content is acceptable).
See the FAQ Section in the 3L Mercury Forum for TONS of other Optimax-Pertinent information.
Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
Still consider myself a "Marine Apprentice" after 48 years (learn something new every day).
Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor
My 2012 75 hp. Optimax has been run on 87 octane with 10% ethanol all its life because non-ethanol 87 octane fuel is not available in my area except for 91 octane, and never had a problem. I do use " Don's Prefered Cocktail" in every tank all the time.
2. Correct octane rating for your engine (87 OCTANE)
Your post say's minimum of 87 so was not sure if 89-90 would be acceptable or preferred. The station I get my non ethanol gas does a good business. Not as much as costco but pretty darn good.
I do use the cocktail religiously.
I would opine that clean and fresh gasoline from a high volume station is the best. Costco for instance. While fueling up one day a tanker truck was there. The attendant told me they see three to four trucks a day delivering gasoline.
Adding fresh gasoline to stale gasoline won't freshen up the old stuff. Would be like mixing sour milk with fresh milk.
Mercury states X octane minimum. As in more maybe, but never less.
Ethanol seems to be more problematic than octane. If the choice were say 87 octane with 10% ethanol or 89 octane with 0% ethanol, I would choose the 89 octane.
My 150 Optimax has never seen anything but top-tier 87 ethanol from a high traffic station always with Don's recommended cocktail. My tank holds 42gals and I rarely ever use that much in a season, so usually top off tank with 89 when my fishing season ends. Unlike most, I fish winter time, not summer.Originally Posted by bbcman
Folks get wrapped up over the word 'minimum', in Mercury's application, it means "no less than" not "higher is better". Don's "choose your fuel" guidelines make that abundantly clear.
Last edited by SilverFox579; 04-09-2025 at 07:44 AM.
_______
Phil
'09 Hewescraft ProV
'09 150 Optimax
As someone that's been working on Mercury outboards AND Mercury fuel systems for a number of decades, at least two of which involve Ethanol content: Your choice is backwards.
Engines rated for 87 octane were CALIBRATED on, and for, that fuel. Since higher octane fuels burn SLOWER and COOLER, using 89, 90, 91 or higher does not do you ANY good. As a matter of fact, it can produce less power, burn incompletely, reduce fuel economy, result in carbon buildup, and over time- can even lead to decreased engine life.
Choose wisely.
Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
Still consider myself a "Marine Apprentice" after 48 years (learn something new every day).
Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor
So EuropeanAM I pretty much follow your direction when it comes to my motor, so just 1 final question. If it was your motor (hypothetically) and the choice was between 89 ethanol gas with treatment and 89 non ethanol with treatment which would you chose all thing being equal hypothetically?
I guess I am leaning towards 10% or less ethanol treated fuel, which in the long run will be cheaper.
I will add a different question.
The area I live in does not have non ethanol gas so I always use 87 and Don's cocktail.
Is it recommended to use non ethanol 87 when available sporadically or is that just a waste of money and it wouldn't help anything?
Thank you
Fuel density is higher so a slight MPG increase, in an automobile at least. Ethanol does have an advantage in minimizing carbon buildup though.
Guys, your engines were calibrated for peak performance by Mercury with 87 octane containing up to 10% ethanol. Don's recommended cocktail applies whether or not you use ethanol.
In the 16yrs since new, my 150 Optimax has never seen a drop of non-ethanol and every drop has been treated with Don's cocktail. I can tell you my engine runs as good today as when new. No engine fuel lines have ever been replaced including the black fuel stub it left Mercury with. The only fuel lines replaced were the non-ethanol safe fuel lines (Mercury w/red lettering) my dealer used from tank to bulb and bulb to fuel stub.
The only time I use 89 octane is if I forget to top off my tank at the end of my season, so, as a hedge against octane degradation I'll top off with 89 octane - at most that amounts to 10 - 15gals in my 42gal tank.
There are more important things to worry about with an Optimax than debating whether to use higher octane than recommended and ethanol or not - really.
_______
Phil
'09 Hewescraft ProV
'09 150 Optimax
What is confusing to some is that Mercury Marine is saying use XX octane minimum. Inference to some being that more is OK but less is not.
In several instances Mercury Marine says use XX (87 in one instance) octane minimum and then goes on to say premium gasoline with a rating of YY (92 in this instance) is also acceptable.
Octane is addressed in one, or maybe two, short worded sentences.
However, Mercury Marine then goes into much greater length as to the hazards of alcohol in gasoline. Several paragraphs of many words.
Leading some to believe that it is Mercury Marine's position that the evils of ethanol might be worse than the evils of the use of octane that is above the minimum rating.
At least there is no FAA to force user's to follow their directives. In aviation there is no choice. All outboard motor owner's are free to do as they wish. Hopefully finding that which works best for them.
One of the very few things that folks pay for out of pocket where "minimum" and "acceptable" seem to be unclear.
Funny thing is... oftentimes the same people who want to save money on oil by finding something "less expensive".
Dual Mercury Master Technician- for Mercury Outboards, Mercruiser and Mercury Racing at European Marine in Greenville, SC.
Still consider myself a "Marine Apprentice" after 48 years (learn something new every day).
Mercury Parts, Mercury Outboards, Smartcraft & Accessories, Injector Service, TDR Reeds- BBC Sponsor
Reply With Quote
