Reply With QuoteCheck your manual for starters to see if Mercury make a recommendation. Personally - both my outboards run on 91 without issue (One E-Tec and one Merc 2 stroke) - just make sure there is no ethanol in it.
which fuel is best to use ?
Which fuel should I be using for my mixture for a 2008 Mercury 2 stroke 4hp outboard?
91 95 98 ?
Have been using 98 but have heard people running lower octane and getting a smoother idle and smoother running....
Check your manual for starters to see if Mercury make a recommendation. Personally - both my outboards run on 91 without issue (One E-Tec and one Merc 2 stroke) - just make sure there is no ethanol in it.
I haven't had the motor since new so I don't have a manual for it.
Bit I just read the below article and it seems so long as you use the correct semi synthetic oil suitable for use with high octane such as TC-W3 it's all good, which is the type of oil I use
https://www.tradeboats.com.au/traile...till-aint-fuel
.......Ash
If your fuel sits for a while between trips not a bad idea to go a higher octane when filling up
http://mercurymarine.sv7076.si-serve...outboards.aspx
accordording to this, for my motor, the only mention of octane rating is to use a minimum of 91, no mention of not being able to use 98 octane....
.......Ash
My local sells 91 e10 or 98 so I use 98. The mariner 6 chews it up no problem.Originally Posted by ashh
My preferred is 95 but getting less common.
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nil carborundum illegitimi
Was told by the boat supplier to only use regular 91 on my new Mercury 150, and especially not E10 I think it readily absorbs moisture more than the regular.
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Is 91 guaranteed to be ethanol free?
98 is fine - I use BP98 in my Yammy 6 hp 2 stroke with stabil storage in the tank. The Mercury recommendation you posted only mentions a min of 91 and no max octane rating so your good to go with 98 if that is your preference.
Soon you won't get 91 without ethanol...getting harder even now. I use 98 anyway because my American iron diesels on 91.
Here's how it goes IMHO and backed by a friend in the industry. Based on what is being supplied from overseas and what is in short supply at the pump you might get as stated below. We import fuel already processed for over 90% of our requirements. The octane displayed at the pump is the minimum, it can be higher and most modern cars can automatically adjust to a change in octane.
now,
91 can be either 91 or 95 octane.
95 can be either 95 or 98 octane
98 can only be 98 octane.
Based on the above if you filled your tank with 91 octane but the servo had 95 in the tank (it happens every now and then, about 3 years ago this was the case for nearly 2 months continuously) and you tuned your motor then as you continued to fill your tank and progressively added 91 octane you would find your motor suffering slightly. This happened to me.
Now if you fill with 95 octane only and get the occasional 98 octane in your tank it won't have a problem as the previous scenario. 98 octane in most instances will not alter the performance of most outboards and indeed car engines unless they have been designed for its use, contrary to what most people think.
Just for something to think about in most of Europe you won't even find 91 at servos, it's usually 95 or 98.
Use 95 octane, look around, I found a servo (at Glenview) that has 95 octane slightly cheaper than 91 octane on the Sunshine Coast, all the time. Even 98 octane is usually 5 cents dearer. Yes I have to drive 10 - 15 mins but it is worth it plus the boss and I then do some side trips to different localities and in the process have found some awesome places to have lunch and some great scenic views. I use jerry cans for the boat as the pumps are too fast and blow back.
PS. Even my whipper snipper, blower etc runs better on 95. This also begs the question why the different octanes vary so much in price, it's because the fuel suppliers can and no matter what we do or even anything the govt does they totally ignore us. The govt is not really interested as any reduction in exise in fuel hurts their income upon which they have become reliant (never used to be the case).
This info is copied from the mercury marine 150 HP 4 stroke owners manual -
FUEL AND OIL
Fuel Recommendations
IMPORTANT: Use of improper gasoline can damage yourengine. Engine damage resulting from the use of impropergasoline is considered misuse of the engine, and damagecaused thereby will not be covered under the limitedwarranty.
FUEL RATINGS
Mercury Marine engines will operate satisfactorily when using amajor brand of unleaded gasoline meeting the followingspecifications:
USA and Canada ‐ having a posted pump Octane Rating of 87(R+M)/2 minimum. Premium gasoline [92 (R+M)/2 Octane] isalso acceptable. Do not use leaded gasoline.
Outside USA and Canada ‐ having a posted pump OctaneRating of 90 RON minimum. Premium gasoline (98 RON) is alsoacceptable. Do not use leaded gasoline.
So according to the designers if you use fuel between 90 & 98 octane rating unleaded it will operate as designed & not void warranty. It goes on further to talk about ethanol -
"The fuel system components on your Mercury Marine engine willwithstand up to 10% alcohol content in the gasoline. We do notknow what percentage your boat's fuel system will withstand.Contact your boat manufacturer for specific recommendations onthe boat's fuel system components (fuel tanks, fuel lines, andfittings). Be aware that gasolines containing alcohol may causeincreased:
- Corrosion of metal parts
- Deterioration of rubber or plastic parts
- Fuel permeation through rubber fuel lines
- Starting and operating difficulties "
I'm not sure if the original poster had considered exactly what the octane rating means, I personally don't think The average boat user would notice a performance difference in the engine regardless of which fuel you use (between 90 & 98) if your engine is in good condition & tuned correctly. The Octane rating is merely a number used to designate the fuels resistance to detonation when under compression, it has no relevance to calorific value which is how much energy is contained within a given quantity. the use of a higher octane rating fuel in an engine will result in a slightly lower fuel burn due to the Vaporised fuel igniting closer to the optimum piston position during its stroke, but this comes at a higher cost due to pump price. You'll get benefit with this in a high use road vehicle but in a recreational boat engine which might get 1000 hrs over many years I'm not sure the savings in fuel use would be very high. Someone with a modern engine recording the fuel flow could provide some good info here if they were to do an experiment.
My summary - if the cost of the fuel is not an issue for you then definitely the higher octane rating will give a slightly less fuel burn & a higher resistance to detonation, resulting in less mechanical stress on the engine components.
- if the cost of the fuel is an issue for you then using 91 or 95 octane rating will be fine.
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