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Suzuki 300 Octane vs. Fuel Economy

Old 02-11-2021, 09:48 AM
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Default Suzuki 300 Octane vs. Fuel Economy

Does anyone have any evidence that running a higher octane will yield better fuel economy? If so, by how much.

I just did two fill ups at a reasonably local marina for a total of about 200g - don't remember octane but was cheapest around for E-free. . For the most part I struggled to keep over 3mpg which is normally easy to achieve. Was it how I loaded the boat? Extra wind resistance? who knows but it did get me thinking about the above question.

Walmart just opened up 92 octane e-free. It is less than I can get e-free on the water but more than WaWA at 89 octane by 7-8%. All other things being the same, does it make sense to pay a few percent more for higher octane at Walmart vs. Wawa?
Old 02-11-2021, 10:40 AM
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Your outboard will get the same economy at the specified octane as any octane higher than specified. If you run lower than specified octane gas in your outboard you could see a slight decrease in economy. E10 vs non ethanol gas of the same octane will have a 2-3% mpg increase.
Old 02-11-2021, 12:12 PM
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My 2019 300APs require 89 octane.Running higher octane then whats recommended does nothing but burn money. Running under can cause damage and reduce your MPG.
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Old 02-11-2021, 03:43 PM
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Originally Posted by wstanford277 View Post
Your outboard will get the same economy at the specified octane as any octane higher than specified. If you run lower than specified octane gas in your outboard you could see a slight decrease in economy. E10 vs non ethanol gas of the same octane will have a 2-3% mpg increase.
I have proven the opposite on my own boats and vehicles numerous times but here are the facts to back it up. E Gas only benefits farmers and the people they.... err well, I’ll just keep this out of the bilge.

Old 02-11-2021, 03:54 PM
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Originally Posted by HighTechRedneck View Post
My 2019 300APs require 89 octane.Running higher octane then whats recommended does nothing but burn money. Running under can cause damage and reduce your MPG.
I agree but the knock sensor on all the DF engines guard against damage from sub 89 octane and AP engines won’t go into lean burn mode under 89. I wouldn’t be scared to run < 89 in a pinch but wouldn’t use it exclusively.
Old 02-12-2021, 06:22 AM
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Originally Posted by kmoose View Post
I agree but the knock sensor on all the DF engines guard against damage from sub 89 octane and AP engines won’t go into lean burn mode under 89. I wouldn’t be scared to run < 89 in a pinch but wouldn’t use it exclusively.

Did not realize they would not go into lean burn below 89 octane.....doesnt matter never run anything below that anyway.
Old 02-12-2021, 08:01 AM
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Originally Posted by kmoose View Post
I have proven the opposite on my own boats and vehicles numerous times but here are the facts to back it up. E Gas only benefits farmers and the people they.... err well, I’ll just keep this out of the bilge.
Sorry - I transposed E10 and non E gas.
Old 02-12-2021, 09:13 AM
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Originally Posted by kmoose View Post
I have proven the opposite on my own boats and vehicles numerous times but here are the facts to back it up. E Gas only benefits farmers and the people they.... err well, I’ll just keep this out of the bilge.
This is good info. Just want to add something to consider...
Power is affected by the BTU content of the fuel. More btu's/lb. Gasoline has more btu/lb than Alcohols. Diesel has more than Gasoline. This affects mileage, or amount of energy/gal.
Summer gasoline has more btu's/gal than Winter blend. Winter blends have a higher blend of Light End compounds, made up of smaller Carbon molecules, which have a higher vapor pressure in cold weather, and your car will still run.
So yea, straight Gasoline yields more power than Alcohol blends, and Summer fuel has a bit more energy/lb than Winter blends.
Old 02-12-2021, 11:18 AM
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Originally Posted by kmoose View Post
I agree but the knock sensor on all the DF engines guard against damage from sub 89 octane and AP engines won’t go into lean burn mode under 89. I wouldn’t be scared to run < 89 in a pinch but wouldn’t use it exclusively.
?????
I can't find any reference to a knock sensor in the service manual or lean burn to octane relationship.

Old 02-18-2021, 09:59 AM
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Originally Posted by a7ewizard View Post
?????
I can't find any reference to a knock sensor in the service manual or lean burn to octane relationship.
Here you go...


Old 02-18-2021, 12:01 PM
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I can tell you this:

My DF300AP (2017). If I run 87 Octane E10 from the pump, my MPG goes down 10% compared to Rec90. I thought I was imaging it... but I have 100% verified it.
Old 02-18-2021, 02:36 PM
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Originally Posted by OldPete View Post
I can tell you this:

My DF300AP (2017). If I run 87 Octane E10 from the pump, my MPG goes down 10% compared to Rec90. I thought I was imaging it... but I have 100% verified it.
Makes perfect sense. Running lower than minimum recommended octane detunes your engine by way of knock sensor retarding the timing. I run only rec 90 or higher.
Old 02-18-2021, 03:56 PM
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Originally Posted by lifestarts@forty View Post
Makes perfect sense. Running lower than minimum recommended octane detunes your engine by way of knock sensor retarding the timing. I run only rec 90 or higher.
Actually, IIRC the DF300AP is designed for 87 octane... so I do not believe it is a function of octane... it's a function of ethanol.
Old 02-18-2021, 04:27 PM
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Ethanol will absolutely reduce fuel economy. In tuner cars running E30-E85 there is usually 15-25% more fuel used vs 100 octane no E. (100 = E70 effective octane) Will the increased fuel efficiency offset the increase in cost with such a small amount? It's a toss up IMHO and I would just go with the cheapest ethanol free fuel for maintenance sake, octane above the rating of the motor won't do much of anything.
Old 02-18-2021, 04:42 PM
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Originally Posted by lifestarts@forty View Post
Makes perfect sense. Running lower than minimum recommended octane detunes your engine by way of knock sensor retarding the timing. I run only rec 90 or higher.
Df300 don't have a knock sensor. Df115, Df140 and Df350 do ( and maybe others).

No reference to a knock sensor in my Df300 service manual. Not shown in the exploded parts diagrams available online ( but are shown for the other engines).


Old 02-19-2021, 06:47 AM
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I’m not familiar with any of the Suzuki outboards. But I don’t see how any EFI-ECU controlled motor could operate properly without a knock sensor.
Old 02-19-2021, 07:23 AM
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Originally Posted by Cmw225 View Post
I’m not familiar with any of the Suzuki outboards. But I don’t see how any EFI-ECU controlled motor could operate properly without a knock sensor.
How do you define 'properly'? It's a good idea to have one but certainly not a necessity. Carbureted engines don't have them.
Old 02-19-2021, 07:46 AM
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we're talking apples and oranges here. E10 vs non-E, 87 octane vs 89+. Both E10 and lower octane affect performance. I run E10 b/c there are limited options for non-E where I am, and depending on where I get gas some docks have 89 only, some offer 87 or 92. I use 89 or higher as per my manual.

To the OPs question, it does not make sense to get 92 if you can get 89. NOW, if you mistakenly put in a tank of 87, then topping off w/ 92 will help.
Old 02-19-2021, 08:47 AM
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Originally Posted by drkptt View Post
How do you define 'properly'? It's a good idea to have one but certainly not a necessity. Carbureted engines don't have them.
I don’t think a knock sensor would do any good on a carbureted engine anyway.

Carbureted engines are mechanically control. With pre set parameters and manual adjustment. ( Carb jet size and manual ignition timing advance controlled by throttle position as examples) Which works really well just not very efficient.

EFI engines are electronically controlled via computer ( ECU-ECM). The computer relies many sensors ( a knock sensor usually being one of them) to keep the engine running properly with optimum efficiency and performance.


Old 02-19-2021, 09:06 AM
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Originally Posted by wstanford277 View Post
Your outboard will get the same economy at the specified octane as any octane higher than specified. If you run lower than specified octane gas in your outboard you could see a slight decrease in economy. E10 vs non ethanol gas of the same octane will have a 2-3% mpg increase.

Good to know.

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