Running 87 Octane in my Mercury 4 Stroke

[Happybeerbuzz]

My Tracker 40HP is the one and only boat I have ever owned.  When I bought it, the dealer said run 87 octane in it and that is all I have done.  Not for any particular reason, I am wondering if 87 is a minimum, not necessarily exactly what I should be using.  Is 87 octane exactly what I should be using or a minimum?  What about with the 10% ethanol content? 

 

[gim]

Is the 87 octane ethanol free? the presence of ethanol is the issue, not necessarily the octane.
 

It’s generally fine to use normal gasoline if you don’t allow your engine to sit unused for long periods of time. I see your in Cali, so my guess is that you can fish all year long. If your outboard goes unused for longer periods of time, I would use non-ethanol fuel.

 

I have a 75 4-stroke Merc and always put 91 octane ethanol free premium fuel in it because mine will go unused for 5 months in the winter. Same with my snow blower and lawn mower, which are only seasonally used.

[Tennessee Boy]

Mercury recommends 87 octane up 10% ethanol.   I would consider that to me a minimum but I wouldn’t go any higher unless the gas sets in the tank for long periods.  Ethanol turns into a gooey gel as it’s exposed to water in the fuel or moisture in the air.  Gooey gel is not good for engines.   I loaned my power washer to someone who put ethanol fuel in it.  It sat for several months and would not run after that.  I had to take the carburetor off and clean the gooey mess out of it and unclog the jets.

[Jig Man]

The techs at the dealerships where I go have always been skeptical about ethanol in gasoline.  They are Mercury factory trained and recommend 91 ethanol free fuel along with Quickleen and Quickcare.  I do this without fail every time I get gasoline.  It worked for 14 years in my two stroke Optimax and has worked for 7 years in my four stroke Verado.

[Happybeerbuzz]

56 minutes ago, gimruis said:

Is the 87 octane ethanol free? the presence of ethanol is the issue, not necessarily the octane.
 

 

Typically, it is not ethanol free.  I have looked for stations around me, but there are none that are close.

 

Are higher octane fuels typically ethanol free?  The pumps with ethanol typically say "may contain up to 10% ethanol".  Sometimes there are pumps without those stickers.  However, I do not see any that boast ethanol free. 

 

[Jig Man]

If I were in that situation I would definitely be adding Mercury Quickcare to my boat gas.  It just takes a little bit.  I believe it is 1 oz per 10 gallons.

[galyonj]

1 hour ago, Happybeerbuzz said:

Are higher octane fuels typically ethanol free?

 

No.

 

Around here, at least, stations with 0% ethanol fuel make a big deal about it. Signs and all that. Plus it costs more. 

[J._Bricker]

@Happybeerbuzz, I’d continue to use a quality 87 Octane gasoline religiously as the dealer recommended in your Merc. When I ran mid grade or premium in old my Opti I had some problems due to the longer burn time. The new 4 stroke Mercurys (ProXS) specify 87 Octane.

[Kirtley Howe]

2 hours ago, gimruis said:

Is the 87 octane ethanol free? the presence of ethanol is the issue, not necessarily the octane.
 

It’s generally fine to use normal gasoline if you don’t allow your engine to sit unused for long periods of time. I see your in Cali, so my guess is that you can fish all year long. If your outboard goes unused for longer periods of time, I would use non-ethanol fuel.

 

I have a 75 4-stroke Merc and always put 91 octane ethanol free premium fuel in it because mine will go unused for 5 months in the winter. Same with my snow blower and lawn mower, which are only seasonally used.

My boat motors have always had ethanol free gas, as it unfortunately can sit unused for several weeks at a time during the summer, and all winter. My lawnmowers, weedeaters, and motorcycle get 87 unleaded with 10% ethanol.....until late in the fall. Then I run ethanol free in all of them for the last few times I use them. They then all get treated with a gas stabilizer and filled up completely with ethanol free gas for the winter. I do this because ethanol free gas is MUCH more expensive than regular gas around here....and I am cheap. So I only use the ethanol free gas in machines that are going to sit unused for any length of time or are being stored for winter. 

[Kirtley Howe]

17 minutes ago, J._Bricker said:

@Happybeerbuzz, I’d continue to use a quality 87 Octane gasoline religiously as the dealer recommended in your Merc. When I ran mid grade or premium in old my Opti I had some problems due to the longer burn time. The new 4 stroke Mercurys (ProXS) specify 87 Octane.

 About that longer burn time....a friend of mine has a Harley motorcycle. It has been extensively modified and is running a much higher than stock compression ratio. He runs only the highest octane ethanol free gas he can get.  He loves it, or did, until he rode the Blue Ridge Parkway one year. He found out that high octane gas, high compression engines, and high altitude don't mix. At the highest elevations on the Blue Ridge, his bike would only start by coasting it downhill and dropping the clutch and it would barely run until he got back down to a lower altitude. 

[airshot]

Use what the mfgr recomends, they know best !!!  The E10 fuel dilemmas are self served, gotta have something to blame poor maintenence on !!  Been using it since it came out in all my toys, not one single issue !!  I do use fuel stabilizer as recomended, especially for storage over 60 days.  Yourvengine is set up to burn 87 octane, going higher in octane makes fuel burn more slowly, so you can loose performance by going higher, numerous studies have shown this to be true.  My neighbor is an old car guy, probably has about 20 plus old cars from 50's and up. He uses E10 in all if them with O issues, but...he has upgraded all the fuel lines and stuff to be E10 compatible.  He adds a few oz of stabilizer into his fuel, his car's sit for often over a year with O issues except the batteries !!   The alcohol is a cleaner, when regular fuel is used, it leaves a residue, when you switch to E10, it cleans all that gunk out and causes issues !!   Clean your fuel system before going to E10 and you would be fine....again numerous articles were written about preparing your vehicle for E10 when it came out, but no one paid any attention to them, so....they had issues !!  Use what the mfgr recomends andvyou will get the best performance from your motor !!! Yes...do add a little stabilizer when you fill your tank and all will be good !!!

[gim]

More often than not it’s the components leading to the engine that fail because of ethanol, as @airshot stated above. If you want to run fuel with ethanol, upgrading those components is a wise move. If you don’t want to make those upgrades, simply using an ethanol free fuel will also eliminate the problem.

 

Ethanol free gasoline obviously does cost more. For me it’s worth buying to completely avoid problems with ethanol in gasoline for my seasonal engines. Plus it’s readily available around my house. I fill my boat up with gasoline about twice in 6 months. It’s been so freaking dry here my mower isn’t getting used much either.

[Woody B]

Ethanol is not the devil many people think it is.   There's several reasons for it's reputation.  When ethanol was first put in gasoline many vehicles, boat motors, and small engines had fuel system components that weren't compatible with ethanol.   Also some of the older 2 stroke oils weren't compatible either.  Modern engine, and modern 2 stroke oils are now compatible.  

 

The other problem with ethanol.  It's hygroscopic.  It readily absorbs moisture.  If a boat, vehicle, or small engine sits a bunch I recommend using fuel stabilizer as well as ethanol free gasoline.  If you're going to burn the contents of the tank is a month or so don't worry about it.  Regardless of fuel type used it's best to keep the tank full.  IE, if you've got a 30 gallon tank, and you normally use 30 gallons a month I recommend filling it every week or 2 instead of just once a month.  Air space in the tank is one place moisture comes from.   

 

So, the magic part about ethanol.   It absorbs moisture.   Gas and water don't mix.   Let's say you have a 30 gallon tank.  It's 1/2 full, and sits for a few weeks in a humid area.   It's very likely the tank will sweat.  Condensation will form inside the tank.   Water is heavier than gas.  It will go to the bottom of the tank, where the fuel pickup is.  This will cause some problems.   However, IF the 1/2 full tank that sits and forms condensation has 10% ethanol it can absorb moisture with no ill effects.   The ethanol separation only happens if the volume of water is too much for the ethanol to absorb.  Take 15 gallons of ethanol free gas and pour a gallon of water in it.  You're going to have problems.  Take 15 gallons of E10, pour a gallon of water in it, and you'll never know.  (don't actually try this, there's probably already some moisture in it)   

 

I only use 87 octane "regular" gas in my 4 stroke.   I checked the ethanol content a couple weeks ago and it was only 4%.   E10 "can" have "up to" 10% ethanol, but it isn't required to have any.   (I have access to a meter to check ethanol content)    

 

The only thing I own that I use ethanol free gas in is my generator.   It sits, sometimes for years.  I use ethanol free gas, and stabil.  I start it once a month, but only for a few minutes.   

 

I'm not a marine technician.  I'm an ASE Certified Master Automotive technician, and a General Motors World Class tech with 41 years experience.   I've also burned thousands of gallons of methanol (kinda like ethanol X10) in race cars.   

 

 

[Bird]

When I was doing small engine repair out of my garage as a side business years ago I saw first hand the effects of ethanol shortly after it showed up at the pumps.

As mentioned ethanol draws moisture into the fuel and this moisture settles below the fuel causing corrosion and piting in the carburator.

 

Anytime someone would bring me a chainsaw that sat for months with ethanol fuel, I'd simply order a new carburetor.

Sitting is the culprit.

 

[T-Billy]

My mechanic recommends 87 octane along with a good fuel conditioner. 

[Captain Phil]

I only use REC 90 ethanol free gasoline in my Merc 4 stroke.  It's readily available here in Florida.  My boat often sits for weeks at a time and I feel it's good insurance.

[GPtimes2]

If your manual says 87 is fine then it is designed to run with it. Higher octane is to inhibit pre-detonation. Some engines (high performance) run hotter and can cause ow octane fuel to ignite in the cylinder before the spark. This generally caused pinging/nocking noises. Maybe in some cases if your motor is running hotter than it should on a very hot day and under heavy load, you may have a need for a little higher octane.

Ethanol has a little (maybe 1 or 3%) less energy. Same with winter blend gas. But the cost for no ethanol or summer blend out way the energy (milage) improvement.

You can add sta bil to your gas and it will be fine for up to 2 years.

A LOT of wasted money being spent on gas that is not called for or needed.

 

[airshot]

On 6/17/2023 at 3:53 PM, T-Billy said:

My mechanic recommends 87 octane along with a good fuel conditioner. 

Fuel conditioner should be a must for any sitting fuel over 30 days.  Non ethenol fuel also degrades, just look at the bottom of the fuel bowl after sitting, see thar brown crap...we called that gasoline varnish, was about the same color as varnish !