Question on boat fuel: Hey everyone asking for your thoughts on fuel. When available I try to use ethanol free in my Merc 200, but do you have a preference on octane? My owner's manual...

Jim Sargent Loc: Payson, AZ

Hey everyone asking for your thoughts on fuel. When available I try to use ethanol free in my Merc 200, but do you have a preference on octane? My owner's manual advises minimum 87 but says it's okay to use 91. The dealer said 87 but I recently fished with a very experienced angler who advised 91. Do any of you have experience with this issue that would sway you one way or another?

Thanks for your input.

MuskyHunter Loc: Torrington, CT

Jim Sargent wrote:

Hey everyone asking for your thoughts on fuel. When available I try to use ethanol free in my Merc 200, but do you have a preference on octane? My owner's manual advises minimum 87 but says it's okay to use 91. The dealer said 87 but I recently fished with a very experienced angler who advised 91. Do any of you have experience with this issue that would sway you one way or another?

Thanks for your input.

I use whatever fuel the manufacturer specifies. They know better more than anyone. The only exception to that is when I store the boat for the winter. I then use non-oxy to prevent phase separation which can easily happen when the boat sits for a long period of time. I been using unleaded 87 since 1987 (my first boat) and have never had a problem and I put a lot of hours on the boat.

The boat does not perform any differently in the spring when using the non-oxy fuel than it does for the rest of the season. My instrumentation tells me miles per gallon and that is also unchanged. So no mileage benefit for higher octane fuel.

Higher octane fuel is meant to stop detonation in high compression engines. Using this in a lower compression engine slows the burn rate and reduces efficiency. You can search the web for reputable sites and find this same information. Basically, octane does not equate to more power or efficiency.

https://resource-center.meineke.com/using-premium-gasoline-really-save-money/

D Tong Loc: San Francisco,Ca

I’ve owned 5 Boats and I’m sure some will argue with me but I find anything over 87 octane is a waste you really don’t need it higher also use the different types of additives for gas treatment especially if you have your boat sitting for any period of time

mdegraw

Agree with above. I'll often go with the ethanol-free gas if I know I won't be using the boat for a few weeks (not just the winter). If you're running your outboard regularly, reg. gas (with ethanol) should be fine, unless your owners manual says otherwise. Be aware, the Biden administration is considering, as we speak, raising the allowable alcohol content in gas from 10 to 15%, a bad move in my opinion.

MuskyHunter Loc: Torrington, CT

mdegraw wrote:

Agree with above. I'll often go with the ethanol-free gas if I know I won't be using the boat for a few weeks (not just the winter). If you're running your outboard regularly, reg. gas (with ethanol) should be fine, unless your owners manual says otherwise. Be aware, the Biden administration is considering, as we speak, raising the allowable alcohol content in gas from 10 to 15%, a bad move in my opinion.

Yes, do not put 15% ethanol in a boat. No boat motor is designed for that!

Jeremy Loc: America

Jim Sargent wrote:

Hey everyone asking for your thoughts on fuel. When available I try to use ethanol free in my Merc 200, but do you have a preference on octane? My owner's manual advises minimum 87 but says it's okay to use 91. The dealer said 87 but I recently fished with a very experienced angler who advised 91. Do any of you have experience with this issue that would sway you one way or another?

Thanks for your input.

Modern equipment can handle the lower octane.

When you see the sticker on a fuel pump that is the minimum it will be. Standard Gasoline octane can fluctuate quite a bit drop to drop. Alcohol became a racing fuel due to its very consistent octane rating drop to drop.

The higher octane fuel burns slower in the combustion chamber. If electronics etc are tuned to accept the lower octane you may gain a little performance with the higher octane but it may be very hard to notice.

In the old days ignition timing had to finely tuned for the quicker burning ( lower octane ) fuels.

Higher octane fuel can provide more power ( if the ignition timing / compression is proper ) because every time piston is pushed down by the explosion it pushes them for a longer period of time. Unless racing and constantly making these adjustments it may not be worth the effort.

Larry B Loc: Key Largo, FL

In the Keys non ethanol is known as Rec90 or R90 the octane is 90

Jim Sargent Loc: Payson, AZ

Thank you all for your replies.

captjim Loc: Antioch Ca

My biggest concern is that the modern fuels loose octane when sitting for a long time. As well "gumming" up carburetors or fuel injection. I would add a bottle RESTORE fuel additive if it will sit for more than a few weeks. The marina where I keep my boat sells fuel with the RESTORE additive already in it. When it comes to 91 octane or not. I think it makes very little difference other than price because it won't be 91 octane for long. Most modern electronic ignitions can compensate for variations in octane. The timing will adjust to the octane level to prevent pre-ignition.

Jclester12 Loc: Arizona phx

My old 1988 200 Merc run better on reg fuel, but sometimes mix mid grade if it was sitting a month

Kerry Hansen Loc: Bremerton, WA

Jim Sargent wrote:

Hey everyone asking for your thoughts on fuel. When available I try to use ethanol free in my Merc 200, but do you have a preference on octane? My owner's manual advises minimum 87 but says it's okay to use 91. The dealer said 87 but I recently fished with a very experienced angler who advised 91. Do any of you have experience with this issue that would sway you one way or another?

Thanks for your input.

I always used the higher octane.

jepolt Loc: North East Ohio

Hi Jim,
You will get as many different answers on this as you get replies. I has. Mercury 150 on my tracker for years. The dealer, manufacturers and old timers (like me😁) all said 87 or 89 octane. I used 89 for every tank ever put in her. Never an issue. They all did recommend to keep stabilizer in the tank so every time I put in more than 15 gallons I put the appropriate amount of that in. It helps with all the impurities in the additives used in gas these days.
That’s my two cents. Wish you well and catch lots of fish with that Merc this year!👍

Billy Bob Loc: Terre Haute,IN

I have a 200 HP Evinrude that is 22 years old. Have never used anything but 87 octane with Star-Tron additive. 99.9% of the gas I buy has ethonal in it and no problems.

Lowescatfish18 Loc: Wesley Chaple florida

my 2018 115 mercuy calls for 91 oct. but not all gas station carry 91 so then i put high test in her. if i am below half tank if i only need 1/4 tank full i will put 87 or 89 what ever they have. the only place i can find 91 is at wawa gas station down here in central fl.

tight lines

BarryE Loc: SE Pennsylvania

I always use prem 91/93 plus additives mostly Luca's gas treatment.. At the beginning of the season I'll treat that tank with SeaFoam to clean all the junk out of the carb. I trailer my boat so I Fill at the same gas station.