ETEC 250HO (3.4L) Premium (91 octane) or regular (87) or ... mid-grade (89 octane)???

[5littleones]

This has been going back and forth for as long as I have owned a boat ... for the longest time, I've been told to use unleaded regular ... then a couple of local mechanics said premium ... now in talking to the well know Fuel Injector Man, he said for ETEC's, it's 'designed' for 87 regular unleaded.

Mine is the 2013 model #E250HGLAAD with the magnum lower. What are your thoughts??? What are you using on your ETEC's?

UPDATE: To clarify, my main purpose for asking this question is in regards to carbon buildup in the motor. I understand that Evinrude says minimum acceptable octane is 87. But will lower octane, when used with any given oil, cause more carbon buildup in motors?

[unknown angler]

I run 87 non ethanol, 87 ethanol has about 3 or 4 % ethanol added I think the 91 octane is closer to 10 %.

[ChampioNman]

your motor is designed to run 87 octane up to 10% ethanol.

[5littleones]

your motor is designed to run 87 octane up to 10% ethanol.

Thanks for the info ChampioNman!! Will higher octane help with performance like throttle responsiveness and fuel economy? And does higher octane help reduce carbon deposits in the motor?

[5littleones]

I run 87 non ethanol, 87 ethanol has about 3 or 4 % ethanol added I think the 91 octane is closer to 10 %.

Thanks unknown! haha ... In California, we have little or no non-ethanol fuel available. So all of our fuel is ethanol blends. Wish I could locate non-ethanol fuels. I use Stabil 360 Marine to help combat ethanol in my boat.

[ChampioNman]

Thanks for the info ChampioNman!! Will higher octane help with performance like throttle responsiveness and fuel economy? And does higher octane help reduce carbon deposits in the motor?

No, not really. Actually Premium has a lower flash point than regular and can hinder performance.

[mactlman]

also causes more carbon build up with higher octane

[5littleones]

also causes more carbon build up with higher octane

I have heard that before, but I do not understand ... can you help explain that higher octane causes more carbon buildup?

And thank you and your son for his service!

[jc2bg]

Higher octane runs colder, and because we do not run outboard engines wide open all the time, running colder may not allow the carbon to burn off as completely.

[JR19]

Higher octane has a lower flash point so it burns slightly cooler. Boat motors run several degrees cooler than most other traditional gasoline burning motors. This is a perfect recipe for carbon build up. If they increase the temperature at which a boat motor operates then carbon could be reduced with a hotter burn. However boat motors do not have a closed loop water cooling system so this is impossible. I have seen video of a boat in the winter where the water temp was around 45-50* and the person was idling. If I recall correct their idle temperature on their smart gauge said the motor temp was 130*. They got on plane and the temp dropped to 95*. There rpm went from 700 to 4200 but the temperature went down....that what happens when you force cold water through a motor. They will never get hot enough to cleanly burn away all the carbon.


For the record my E-TECH calls for a min of 87 octane. The Ficht I ran for 14 years prior to that called for the same. I have a local station that only carries non ethanol in 89. Then there is another station that is a few miles out of my way that has it non ethanol in 87. For several years I have bought the 89 octane 95% of the time and on occasion when I fish one particular section of the lake I will stop at the station that has it in 87. Everytime my plugs are changed they look good. I did not change them on my E-TECH because the motor was under warranty so I had an authorized dealer perform the 3 year inspection. I specifically ask him how the plugs looked when I picked it up. He told me they looked like they had a good burn and commented they probably could have ran longer but changing plugs is part of the 3 year schedule. My point is I know 87 is recommended and I run 89 but I don't think running slightly higher will make that big of a difference on carbon build up. I would be more concerned if a person was running 93 or higher and not having high compression heads to burn high octane.

[5littleones]

Higher octane has a lower flash point so it burns slightly cooler. Boat motors run several degrees cooler than most other traditional gasoline burning motors. This is a perfect recipe for carbon build up. If they increase the temperature at which a boat motor operates then carbon could be reduced with a hotter burn. However boat motors do not have a closed loop water cooling system so this is impossible. I have seen video of a boat in the winter where the water temp was around 45-50* and the person was idling. If I recall correct their idle temperature on their smart gauge said the motor temp was 130*. They got on plane and the temp dropped to 95*. There rpm went from 700 to 4200 but the temperature went down....that what happens when you force cold water through a motor. They will never get hot enough to cleanly burn away all the carbon.


For the record my E-TECH calls for a min of 87 octane. The Ficht I ran for 14 years prior to that called for the same. I have a local station that only carries non ethanol in 89. Then there is another station that is a few miles out of my way that has it non ethanol in 87. For several years I have bought the 89 octane 95% of the time and on occasion when I fish one particular section of the lake I will stop at the station that has it in 87. Everytime my plugs are changed they look good. I did not change them on my E-TECH because the motor was under warranty so I had an authorized dealer perform the 3 year inspection. I specifically ask him how the plugs looked when I picked it up. He told me they looked like they had a good burn and commented they probably could have ran longer but changing plugs is part of the 3 year schedule. My point is I know 87 is recommended and I run 89 but I don't think running slightly higher will make that big of a difference on carbon build up. I would be more concerned if a person was running 93 or higher and not having high compression heads to burn high octane.

Excellent info. Thank you!!

For me, I mostly cruise around 3500-5000 RPM ... I will run WOT once a while for a couple mins to try and burn off some carbon ... Give your comments and my usage, 87 is reasonable over 91 ... Right?!

[mactlman]

I have heard that before, but I do not understand ... can you help explain that higher octane causes more carbon buildup?

And thank you and your son for his service!

he would tell you it is "his honor to serve" and thanks!!

[mactlman]

Excellent info. Thank you!!

For me, I mostly cruise around 3500-5000 RPM ... I will run WOT once a while for a couple mins to try and burn off some carbon ... Give your comments and my usage, 87 is reasonable over 91 ... Right?!

run 87 best or 89 fine no need for anymore octane or wasted fuel dollars