What Octane to buy for my boat?

[pulleye16]

I have a 2007 90 HP Mercury Outbooard. Trying to get a real answer on what octane I should place in my boat. Some say the highest I can and others say what the motor recommends which is usually 87 (but says I CAN use higher) Others say it doesn’t matter as long as the least amount of alcohol is used (alcohol can ruin the gaskets / seals???) Am I wasting money with premium gas??? Also, which MN gas stations offer the BEST gas??? I heard BP was good> Sorry so long but does this also comply with ATV's and snowmobiles....

[archerystud]

I run 91 octane non-oxygenated gas in my 115 Merc.

There may be other reasons but from what I've read the oxygenated breaks down faster (1 month vs 3 months) and could gum up in your fuel system. I probably only run 2 full tanks of gas through my engine in a summer.

I do put stabil in the gas before I do put it away for the winter however.

I'm also interested in other opinions here as well.

[Flooringuy]

I have a merc 50 oil injected and I run 87 non-oxy tried 91 and didn't notice any difference.

[fasternu]

My Yamaha manual says to use 87, and anything else will NOT improve performance. Why pay more then? If your fuel is breaking down in only a month, it isn't being stored correctly. If that is the case, it would break down at the refinery before it even got to the store. I have stored many gallons of methanol, which is much harder to keep fresh, for many months without a problem, even through the winter.

[fivebucks]

Flooringguy - where do you get 87 non-oxy? I like to run non-oxy but all I ever see is 91 octane. My 75 Mariner could run just fine on 87 octane but I only run a couple of tanks per summer also and don't want to take any chances. Maybe I am paying more than I need to but I know I am not having repair bills.

[shizzy]

most of the issues with the oxyginated fuel was from older fuel systems. a 2007 should have no issues. if Merc recomends a certain octane, I dont see any benefit to running higher

[jwhjr]

Flooringguy - where do you get 87 non-oxy? I like to run non-oxy but all I ever see is 91 octane.

I was wondering the same thing. I run the 91 non-oxy in my boat and all other small engines.

[BobT]

I have a 2007 90 HP Mercury Outbooard. Trying to get a real answer on what octane I should place in my boat. Some say the highest I can and others say what the motor recommends which is usually 87 (but says I CAN use higher) Others say it doesn’t matter as long as the least amount of alcohol is used (alcohol can ruin the gaskets / seals???) Am I wasting money with premium gas??? Also, which MN gas stations offer the BEST gas??? I heard BP was good> Sorry so long but does this also comply with ATV's and snowmobiles....

Check your outboard specifications. You should be able to find a plate riveted to the motor somewhere. Probably on the outside of the shaft. I can find mine when I raise the motor up and look on the back side of the motor shaft. I have a 98 Johnson 90hp and it specifies 87 octane.

[BobT]

Originally Posted By: fivebucks

Flooringguy - where do you get 87 non-oxy? I like to run non-oxy but all I ever see is 91 octane.

I was wondering the same thing. I run the 91 non-oxy in my boat and all other small engines.

All gasoline sold in MN for the past couple years is required to be oxygenated with 10% ethanol or higher with the exception of high octane, usually 91 or better. I also believe the non-oxygenated fuel is supposed to be reserved for off-road vehicles as well although I have never heard of anyone getting nailed for using non-oxygenated fuel in their vehicles.

[BobT]

most of the issues with the oxyginated fuel was from older fuel systems. a 2007 should have no issues. if Merc recomends a certain octane, I dont see any benefit to running higher

Ditto. In fact, you might find a degradation of performance to use higher than rated octanes because the engine's ignition system is set up for the octane rating specified. Higher octane fuels don't ignite as easily as lower octane because they are more stable fuels and therefore some changes in ignition systems may be needed to achieve optimum performance and efficiency. I know my outboard starts harder and runs rougher when I use high octane. My truck acts pretty much the same way and I notice a decrease in fuel economy as well.

[BobT]

My Yamaha manual says to use 87, and anything else will NOT improve performance. Why pay more then? If your fuel is breaking down in only a month, it isn't being stored correctly. If that is the case, it would break down at the refinery before it even got to the store. I have stored many gallons of methanol, which is much harder to keep fresh, for many months without a problem, even through the winter.

I'll ditto that as well. I've kept 87 octane ethanol blended fuel for years to run my chain saw and it is still working on the same gallon of fuel. I obviously don't use my chainsaw much anymore.

[jigginjim]

Every one has they Ideas. Call a mercury dealor, and ask them.

[jwhjr]

I also believe the non-oxygenated fuel is supposed to be reserved for off-road vehicles as well although I have never heard of anyone getting nailed for using non-oxygenated fuel in their vehicles.

[Flooringuy]

"Flooringguy - where do you get 87 non-oxy? I like to run non-oxy but all I ever see is 91 octane. My 75 Mariner could run just fine on 87 octane but I only run a couple of tanks per summer also and don't want to take any chances. Maybe I am paying more than I need to but I know I am not having repair bills."

Mel's Spicer

[Pat K]

Higher octane gas has a higher ratio of molecules with 8 atoms of carbon to heptane molecules that have 6 atoms of carbon. The higher carbon content is the reason they need better detergent packages in premium gas.

Higher octane gas has a hotter flash point than lower octane fuel. If you are using higher octane gas than the motor was designed to run, you will have more unburned fuel and carbon deposits.

[Flooringuy]

I stand to be corrected on my statement about running 87 non oxy fuel. Double checked here today and it's 91 oct.

Must have looked at the pumps wrong.

Just wanted to clarify that.

[shizzy]

"Flooringguy - where do you get 87 non-oxy? I like to run non-oxy but all I ever see is 91 octane. My 75 Mariner could run just fine on 87 octane but I only run a couple of tanks per summer also and don't want to take any chances. Maybe I am paying more than I need to but I know I am not having repair bills."

Mel's Spicer

a new fuel line, bulb and a carb rebuild will give you rubber parts resistant to the alcohol in the new fuel. I did this on my 1965 Johnson and I run 87 Oxy any day of the week and have never had an issue.

[magnum mike]

Most older fuel lines are not designed to handle the ethanol contained in most gasoline sold in Minnesota. I have seen several fuel lines that become rock hard and actually break due to deterioration due to reacting to the ethanol. You may want to check your manual or dealer regarding any additives also.

[shizzy]

Most older fuel lines are not designed to handle the ethanol contained in most gasoline sold in Minnesota. I have seen several fuel lines that become rock hard and actually break due to deterioration due to reacting to the ethanol. You may want to check your manual or dealer regarding any additives also.

thats the main reason I put the new line and bulb on mine. FYI, the new line is clearly labled "Alcohol resistant" Also I have been told all the rubber parts in cab rebuild kits are alcohol resistant.

$35 in parts for no worries about gas? easy decision for me......

[mrfish1991]

Higher octane is usually meant for higher compression engines. Diesel engines use lower octane fuel because they use compression for ignition and not a spark plug. The higher the octane of the gasoline, the more resistant it is to detination by compression. This is why high compression engines such as race engines and sports cars use the higher octane gasoline.

just a little tidbit about gasoline I learned while working on my science fair project my sophomore year in highschool

[wplatehunter]

I have run 87 in all of my motors with no problems.

[scott b]

I've always used mid-grade. High octane burns hot and was told this is not good for the motor.

[LMITOUT]

The engine manual may say 87 octane is recommended and higher octane will not improve performance, BUT it also says not to use any gasoline that contains more than 10% ethanol. MN's law requires a 10% blend of ethanol at the 87 octane pumps which is right on that recommended limit set by the boat engine manufacturers. It's also known from random testing of tanks that the "10%" number can vary greatly from station to station, so who knows if you're putting 7% or 15% into your boat tank on any given day.

All my seasonal engines get the 91 "proof" non-oxy. Fuel stabilizer or not, gas doesn't have the shelf-life it did years ago and ethanol doesn't help matters either. I will also run my tanks as low as possible before storing so that come spring time it'll get almost a pure dose of fresh gas instead of a full tank of cruddy gas.