Outboard Octane

[Flatrock]

I found the post of ethanol free gas but what octane should I use in this new 4 stroke Merc ? 

(No I don't have docs on my boat yet)

 

Thanks in adv...

[slonezp]

Check the manual. Probably recommends 87

[Fishstalker001]

I have the Merc 150 four stroke and run ethanol free 87. No issues and its been 4 years.  

[tander]

I agree with 87. Most everything I have read says your wasting money if you use over 87 octane in a boat motor but I would call Mercury or wait until you get the docs on your motor.

[Team9nine]

I run two 4-stroke Mercs. 87 octane minimum with cleaners is preferred per manual. However, even better as stated in manual is ethanol free. I run ethanol free whenever I can get it regardless of octane; usually 90 or 91 around here. If you have to use alcohol enhanced gas, manual states 10% ethanol or less, or 5% methanol or less.

[JLBBass]

I'm running non-ethanol gas in my 4 stroke Suzuki, and only octane I can find is 90, so that's what it gets. Better 90 octane non-ethanol, than 87 with ethanol!

[Flatrock]

Thanks guys

[Tennessee Boy]

I have a 2018 Merc 90.  Manual says 87 ethanol free or 90 with 10% ethanol.  I only run ethanol free gas. There are plenty of ethanol-free stations in middle TN.  

[Jig Man]

I always run NON ethanol gasoline.  Around here 91 octane is the only way it comes.  I also add Quickleen and Quick Care to all of the gasoline.  I doesn't cost much and can save a bunch.

[WRB]

Check with your dealer!

Back in Oct 2018, this year, E15 gasoline was approved to replace E10. The impact is 10% ethanol vs 15% ethanol, an increase of 5% regardless of octane. The ethanol is blended at the refinery can add up to 15% and label it E15 depending on supply and demand of ethanol. E15 can be 1% ethanol or anything inbetween up to 15%. E0 is ethanol free gasoline.

Higher octane doesn't damage the 4 stroke power head nor does ethanol. Higher octane lowers pre detonation with 4 stroke engines with high compression pistons. Ethanol acts as a detergent that can affect fuel lines and filters, and may run leaner unless the injectors are designed for higher % ethanol.

I have always used 91 octane gasoline with my 2 stroke OB's unless racing then used 140 oct aviation gasoline, cleaner burning fuel.

Tom

[JoeyT]

I have merc pro xs manual says 87-91 ethanol free if possible. Up my way 87/89 have up to 10% ethanol. I was having some issues with poor idle and performance with th 87 even tho I treat it and only fill boat with what I will use so the gas doesn't sit more then a week. After switching to 91 the motor has never run better...