Premium to e85?
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2013 C300 4matic Luxury
Premium to e85?
Hello everyone, this might be a dumb question, but it's there any special procedures when switching from using premium 91 or 93 octane to e85? I have the 2013 C300 4matic Luxury. It says in multiple places I can use either or. So just wondering if I can just switch the next time I fuel up? Or do I need to do something else first? Thanks in advance for any info!
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From: Northern Indiana
2014 c300 w204.080 3.5 v6
Yeah you dont really need to do anything if its flex fuel it has a fuel sensor. You will not see much if any change unless its a boosted engine that could make use of the higher octane. I dont beat on my car much I have a 14 3.5 v6 engine in my c300 and i only use regular fuel no premium and never had a issue. Its really not worth it.
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From: Northern Indiana
2014 c300 w204.080 3.5 v6
I have a Chevelle with a 600 CID BBC that makes 1000HP on pump E85. I will never switch that car back to gasoline.
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Not 100% true. It is used extensively in the racing world and all over the streets on high compression high power engines. It does require different tuning to be effective and its hella cheap compared to high octane gasoline.
I have a Chevelle with a 600 CID BBC that makes 1000HP on pump E85. I will never switch that car back to gasoline.
I have a Chevelle with a 600 CID BBC that makes 1000HP on pump E85. I will never switch that car back to gasoline.
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From: Northern Indiana
2014 c300 w204.080 3.5 v6
Its exactly the same stuff. I buy it from the pump at speedway and family express locally. E85 is great for making power in high compression or power boosted engines. It can be from E60-E90 and still makes the same power because ethanol dont really detonate like gasoline does.
Last edited by RobertR728; Jan 24, 2026 at 12:28 PM.
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Its exactly the same stuff. I buy it from the pump at speedway and family express locally. E85 is great for making power in high compression or power boosted engines. It can be from E60-E90 and still makes the same power because ethanol dont really detonate like gasoline does.
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From: Northern Indiana
2014 c300 w204.080 3.5 v6
Yes absolutely it doesn't make much sense to run E85 if your not make a lot of power. And yes the mileage sucks as it seems to drop up to 30% in some cars. I dont get very good mileage in my race car 
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From: Northern Indiana
2014 c300 w204.080 3.5 v6
I think @RobertR728 may be referring to high octane racing gasoline like Sunoco 110. It’s not in the pumps even at Sun because it isn’t street legal and can run $6+ per gallon. It’s straight “iso-octane” (2,2,4 trimethyl pentane) plus exotic anti knock alkenes. I don’t think that car in his pic is street legal anywhere on this planet.
Another fun fact about E85 is that more is not better in this case. Ethanol will not ignite from just a spark in the cylinder. So that's the reason for the 85/15 blend. The spark ignites the 15% gasoline that is approx 87 octane then the gasoline ignition ignites the Ethanol for this reason E85 takes a bit more time to ignite and is pretty much detonation proof but higher Ethanol content would be hard on the ignition system to ignite it. I run a 300 fogger nitrous system, normally on a gasoline engine you would pull some timing while spraying NOS but its not necessary with E85. My ignition timing is locked at 36deg and I dont pull any timing when using NOS which would be dangerous on a gas engine. So it can depend on the tune but most of us are running hotter spark plugs and not pulling any timing as the retard is essentially built into the fuel.
My car dont have turn signals or windshield wipers but I drive it all over my town. Another advantage to E85 is the engine runs way cooler because of all the ethanol.
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Estimates vary and depend on the vehicle, but E85 can compromise your mpg by 5 to 30%. And, of course, not every vehicle is compatible with E85. I've noticed a slight drop in mpg with just the 10% alcohol blend. Some of the nearby fuel stops carry clear (no alcohol) gas, but only in 87 octane.
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No need to test the beer -- it is different.
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From: Brazil
C300 Sport 2010
Here in Brazil, the W204 must be fueled only with gasoline; there is no flex-fuel or diesel version. Unfortunately, the regular gasoline here is E30, and the premium gasoline is E25, which probably makes fuel consumption higher than in the US.
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2013 C300 4matic Luxury
