E85
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Mountain Pass
Joined: Jun 2024
Posts: 114
Likes: 24
From: Springfield, Illinois
E85
I've had my truck for 4 years but I forgot how lousy my mileage is on E85 an filled up with it last week.
My brother-in law has a 15 5.0 that he runs E50 in and says he gets 19 or better with but i just haven't drank the cool aide on that yet.
normally with my 16 5.0 I get 14.8 to 15.7 according to the lom , thats on shell 87.
what are you all getting out of your trucks?
My brother-in law has a 15 5.0 that he runs E50 in and says he gets 19 or better with but i just haven't drank the cool aide on that yet.
normally with my 16 5.0 I get 14.8 to 15.7 according to the lom , thats on shell 87.
what are you all getting out of your trucks?
Fleet Mechanic
Joined: Jan 2020
Posts: 1,370
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Most will say 87 is the sweet spot, some do better with a tune on 85. The 85 lower price typically does not offset mpg. Same goes with better octane, 89,91 etc. Higher price doesn't offset mpg, butttt, better octane can give better performance, and that's priceless 
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Mountain Pass
Joined: Jun 2024
Posts: 114
Likes: 24
From: Springfield, Illinois
truck has more giddy up with e85 also with mobil 87 both get less mpg, I don't understand it because my driving habits are pretty consistent.
now when I tow the 30ft camper 8mpg maybe 10 on a smooth stretch, plus I tow in 5th I keep it from shifting into 6th.
now when I tow the 30ft camper 8mpg maybe 10 on a smooth stretch, plus I tow in 5th I keep it from shifting into 6th.
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Joined: May 2005
Posts: 8,235
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From: San Antonio, TX
E85 is not 85 octane. E stands for ethanol, 85 indicates it's percentage of ethanol. So E85 is an 85% ethanol/15% gasoline engine fuel.
Gasoline comes in several octane ratings, commonly 85, 87, 89, 91, 93. 85 octane is usually only seen in ares where the elevation is over 5000'. Octane is a rating to indicate how knock resistant the fuel is. The high the octane, the more knock resistant it is. Higher octane fuel is required for high compression engines, and/ or engines with high performance tunes. Gasoline with those octane ratings will have no more then 15% ethanol, usually 10%.
E85 should only be used in vehicles with engines that are designed for dual fuel use. Those will always have a badge on them somewhere that say Flex Fuel. Those engines are equipped with a fuel system that can adapt to varying levels of ethanol. An engine than is running E85 fuel will typically get 20-25% less fuel economy than when it's ran on gasoline.
Gasoline comes in several octane ratings, commonly 85, 87, 89, 91, 93. 85 octane is usually only seen in ares where the elevation is over 5000'. Octane is a rating to indicate how knock resistant the fuel is. The high the octane, the more knock resistant it is. Higher octane fuel is required for high compression engines, and/ or engines with high performance tunes. Gasoline with those octane ratings will have no more then 15% ethanol, usually 10%.
E85 should only be used in vehicles with engines that are designed for dual fuel use. Those will always have a badge on them somewhere that say Flex Fuel. Those engines are equipped with a fuel system that can adapt to varying levels of ethanol. An engine than is running E85 fuel will typically get 20-25% less fuel economy than when it's ran on gasoline.
Last edited by JKBrad; Jan 5, 2026 at 11:32 AM.
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Mountain Pass
Joined: Jun 2024
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From: Springfield, Illinois
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Cross-Country
Joined: Jun 2025
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E85 is not 85 octane. E stands for ethanol, 85 indicates it's percentage of ethanol. So E85 is an 85% ethanol/15% gasoline engine fuel.
Gasoline comes in several octane ratings, commonly 85, 87, 89, 91, 93. 85 octane is usually only seen in ares where the elevation is over 5000'. Octane is a rating to indicate how knock resistant the fuel is. The high the octane, the more knock resistant it is. Higher octane fuel is required for high compression engines, and/ or engines with high performance tunes. Gasoline with those octane ratings will have no more then 15% ethanol, usually 10%.
E85 should only be used in vehicles with engines that are designed for dual fuel use. Those will always have a badge on them somewhere that say Flex Fuel. Those engines are equipped with a fuel system that can adapt to varying levels of ethanol. An engine than is running E85 fuel will typically get 20-25% less fuel economy than when it's ran on gasoline.
Gasoline comes in several octane ratings, commonly 85, 87, 89, 91, 93. 85 octane is usually only seen in ares where the elevation is over 5000'. Octane is a rating to indicate how knock resistant the fuel is. The high the octane, the more knock resistant it is. Higher octane fuel is required for high compression engines, and/ or engines with high performance tunes. Gasoline with those octane ratings will have no more then 15% ethanol, usually 10%.
E85 should only be used in vehicles with engines that are designed for dual fuel use. Those will always have a badge on them somewhere that say Flex Fuel. Those engines are equipped with a fuel system that can adapt to varying levels of ethanol. An engine than is running E85 fuel will typically get 20-25% less fuel economy than when it's ran on gasoline.
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Joined: May 2005
Posts: 8,235
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From: San Antonio, TX
Correct. I think many people assume it’s 85 octane gasoline, and use it because it’s somewhat less expensive, even if their vehicle isn’t Flex Fuel rated.
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