My vehicle will take E85 and I’ve tried it just to save money. Stick with regular gasoline what you save at the pump will cost you in far more refills. Horrible gas mileage
I’m so fucking confused, man. I’m a tech guy. I’ve spent my whole life getting good with computers, I know very little about cars, and I just can’t keep up. I’ve heard that yeah ethanol is bad but put in your tank what the manual says because if your engine isn’t designed for “high-octane” fuel (???) you’ll damage your car with the pure stuff? But I know how ethanol dries out rubber, which I’m quite sure is what my fuel lines are made of, but my manual says to use 85. So should I be using 87 and avoiding 85? Or…?
I just want an electric car. “Plug it in”, I get.
Edit: Thank you to everyone who responded! It was salient as I was actually driving at the time and saw the comments before my next stop; I ended up getting the right gas thanks to you all. My car immediately started running better. I’m a lot less confused now, I’ll be using 87 gas from now on. Thankfully my car seems to have survived my mistake(s) without any immediately negative consequences >.>
E85 is 85% ethanol, 15% gas (and e15 is the other way around)
Octane rating is a measure of how much you can compress a fuel before it ignites by itself. Higher octane gas is more resistant to that. (And e85 actually has a pretty high octane rating, usually somewhere north of 100. Regular gas often contains up to 10% ethanol, in part because it boosts the octane rating)
To expand on that a bit, if you compress gas enough, at a certain point it just catches fire on its own. This is actually a big part of how diesel engines work. Diesel is actually pretty hard to ignite, in some cases you can even put out small fires by pouring diesel on it (don’t try this at home) so they rely on getting high enough compression in order to work.
Gasoline is a lot more flammable though, you don’t really need to compress it at all for it to burn. Sure, ideally you probably want a certain compression ratio because something something stoichiometry but gas is more forgiving in that regard. As long as your air-fuel mixture is about right, it’s gonna burn when your spark plug goes off.
In fact, gas is maybe a little too forgiving, if your octane rating is too low and your engine compression is too high (mostly a problem with higher-performance engines) that gas can just kind of go off too early before the spark plug goes off, which causes “engine knock” which will cause damage.
But the other way around, high octane in a lower compression engine, basically does nothing spectacular. It still goes boom when the spark plug goes off and not until then.
Just to clarify, the three numbers at the pump (87, 91, 93 I think?) are the octane rating which the other comments explained. The ethanol content is the sticker that says “may contain up to 10% ethanol”. This post is about increasing that percentage of ethanol in regular gas, which as other comments explained mostly just makes the gas less efficient.
E85 is 85% ethanol and 15% gas, basically the reverse of regular gas.
At elevations above 3,500 feet, the air is less dense, which affects how engines combust fuel. Because of this, the risk of engine knocking — where fuel combusts prematurely — is lower at higher altitudes. This allows vehicles to safely run on lower-octane fuel without facing performance issues.
Just use the octane number as required by your car.
The issue with ethanol isn’t directly related to octane. It’s that it can damage rubber parts in the fuel line. Particularly in cars and motorcycles that are several decades or more old. And more than ~15% ethanol would not be advisable for most modern cars as it has different properties than gasoline and your car likely would not run well on it unless you have a bifuel system.
Higher octane fuel (85 vs 87 vs 89 etc) prevents premature detonation in the engine. Detonation needs to happen at a very specific timing in each cylinder (IFF the sparkplug is sparking), but if the fuel is too “eager” to explode it could detonate early just from the heat of the engine, which eventually breaks shit. Octane makes your fuel just a little less explosive, so higher octane rating can compensate for engines more prone to premature detonation (basically most engines that run hotter, high revving, with turbos, some modded engines etc).
Running too high octane doesn’t hurt or help you if you weren’t detonating prematurely before. You’d just be throwing your money away running higher than recommended by the manufacturer (ok it can help clean the engine of carbon deposits similar to how a can of seafoam would, but really you’d be better off using the seafoam, and like seafoam it’d be overkill to do it all the time).
Now using too low an octane rating, it depends. In older cars, you’ll just get premature detonation and it’ll blow shit up, just don’t do it. Most modern cars though are smart enough to adjust their timing to compensate for low octane fuel and avoid damage (check your manual to make sure though). However, you’ll be getting worse performance, worse efficiency, worse emissions, basically your car will drive worse and you won’t actually be saving money with your reduced milage. Unless it’s an emergency and you have no choice, get the recommended.
Octane is basically irrelevant to the issue of ethanol. The relevant issue is that gasoline (ethanol-free) has a specific energy of 47.3 MJ/kg, while ethanol has a specific energy of 29.7 MJ/kg. You need 1.6 gallons of ethanol to get the same energy as a gallon of gasoline.
I don’t think there is a regular 85 octane lowest in Nebraska is 87 octane. E85 is the ethanol version but your vehicle has to be able to use it.
Some 87 here can have small amounts of ethanol if it says so at the pump and that can be used in normal vehicles. Older cars pre2000 don’t run well with it and some with carburators can get vapor lock
I’m a car girl, its mkind of my thing. Octane ratings aretgere to protect your engine, its a rating of how readily the gasoline ignites in the engine. The larger the number the harder to self ignite. Most cars use 85, the only time the higher octane 93 is needed is for cars with turbo or supercharging, or cars with higher compression ratios.
Just put whatever its rated for in it, going with a higher octane than what your car is rated for doesn’t hurt a thing, but it also won’t make your engine run better or anything.
As far as ethanol goes, modern cars ate fine with 10-20% ethanol in their gas. It will get worse mileage the higher the percentage of ethanol as it is not as energy dense as gasoline. The E85 stuff has a higher percentage of ethanol (85%) than is allowed in conventional gas and was introduced to try and lower gas prices (it’s actually completely ineffective and ethanol for fuel is more energy intensive than just giving us straight gasoline but they have to prop up the corn industry somehow). Regular cars can’t use E85 unless they are rated for it as the engine has to add more fuel to keep a close to stoichiometric ratio of fuel to air.
TLDR: Use whatever octane your car asks for, if you put a higher octane in it doesn’t hurt, but it also doesn’t add any benefit.
When it comes to ethanol regular cars can tolerate up to roughly 20% with only a reduction in fuel mileage as a result. E85 is only for cars rated to use it as they need a sensor to detect ethanol percentage and adjust fuel to air ratios accordingly.
Okay so to quickly summarise: the octane number defines just how explosive the fuel is under compression. 100 means it’s the equivalent of a 100% iso-octane mixture.
The more explosive the fuel is, the sooner it detonates as the cylinder compresses it. If it detonates too soon, at too low a compression, that’s when your engine starts to knock. By adding ethanol you’re increasing the pressure needed for detonation, ensuring that the ignition system ignites the fuel at the appropriate time, thus improve the engine’s longevity.
Sounds like a good way to ruin an engine.
My vehicle will take E85 and I’ve tried it just to save money. Stick with regular gasoline what you save at the pump will cost you in far more refills. Horrible gas mileage
I’m so fucking confused, man. I’m a tech guy. I’ve spent my whole life getting good with computers, I know very little about cars, and I just can’t keep up. I’ve heard that yeah ethanol is bad but put in your tank what the manual says because if your engine isn’t designed for “high-octane” fuel (???) you’ll damage your car with the pure stuff? But I know how ethanol dries out rubber, which I’m quite sure is what my fuel lines are made of, but my manual says to use 85. So should I be using 87 and avoiding 85? Or…?
I just want an electric car. “Plug it in”, I get.
Edit: Thank you to everyone who responded! It was salient as I was actually driving at the time and saw the comments before my next stop; I ended up getting the right gas thanks to you all. My car immediately started running better. I’m a lot less confused now, I’ll be using 87 gas from now on. Thankfully my car seems to have survived my mistake(s) without any immediately negative consequences >.>
I think you’re confusing e85 with 85 octane gas
E85 is 85% ethanol, 15% gas (and e15 is the other way around)
Octane rating is a measure of how much you can compress a fuel before it ignites by itself. Higher octane gas is more resistant to that. (And e85 actually has a pretty high octane rating, usually somewhere north of 100. Regular gas often contains up to 10% ethanol, in part because it boosts the octane rating)
To expand on that a bit, if you compress gas enough, at a certain point it just catches fire on its own. This is actually a big part of how diesel engines work. Diesel is actually pretty hard to ignite, in some cases you can even put out small fires by pouring diesel on it (don’t try this at home) so they rely on getting high enough compression in order to work.
Gasoline is a lot more flammable though, you don’t really need to compress it at all for it to burn. Sure, ideally you probably want a certain compression ratio because something something stoichiometry but gas is more forgiving in that regard. As long as your air-fuel mixture is about right, it’s gonna burn when your spark plug goes off.
In fact, gas is maybe a little too forgiving, if your octane rating is too low and your engine compression is too high (mostly a problem with higher-performance engines) that gas can just kind of go off too early before the spark plug goes off, which causes “engine knock” which will cause damage.
But the other way around, high octane in a lower compression engine, basically does nothing spectacular. It still goes boom when the spark plug goes off and not until then.
Just to clarify, the three numbers at the pump (87, 91, 93 I think?) are the octane rating which the other comments explained. The ethanol content is the sticker that says “may contain up to 10% ethanol”. This post is about increasing that percentage of ethanol in regular gas, which as other comments explained mostly just makes the gas less efficient.
E85 is 85% ethanol and 15% gas, basically the reverse of regular gas.
Fun fact, if you go somewhere with high elevation your going to see lower octane ratings. Colorado for example. https://www.slashgear.com/1825420/colorado-85-octane-gas-reason-substitute-87/
That is, and I say this completely sincerely, both the coolest and most fun fact I’ve learned all week. Thanks for sharing!
Just use the octane number as required by your car.
The issue with ethanol isn’t directly related to octane. It’s that it can damage rubber parts in the fuel line. Particularly in cars and motorcycles that are several decades or more old. And more than ~15% ethanol would not be advisable for most modern cars as it has different properties than gasoline and your car likely would not run well on it unless you have a bifuel system.
Here’s my laymen’s understanding:
Higher octane fuel (85 vs 87 vs 89 etc) prevents premature detonation in the engine. Detonation needs to happen at a very specific timing in each cylinder (IFF the sparkplug is sparking), but if the fuel is too “eager” to explode it could detonate early just from the heat of the engine, which eventually breaks shit. Octane makes your fuel just a little less explosive, so higher octane rating can compensate for engines more prone to premature detonation (basically most engines that run hotter, high revving, with turbos, some modded engines etc).
Running too high octane doesn’t hurt or help you if you weren’t detonating prematurely before. You’d just be throwing your money away running higher than recommended by the manufacturer (ok it can help clean the engine of carbon deposits similar to how a can of seafoam would, but really you’d be better off using the seafoam, and like seafoam it’d be overkill to do it all the time).
Now using too low an octane rating, it depends. In older cars, you’ll just get premature detonation and it’ll blow shit up, just don’t do it. Most modern cars though are smart enough to adjust their timing to compensate for low octane fuel and avoid damage (check your manual to make sure though). However, you’ll be getting worse performance, worse efficiency, worse emissions, basically your car will drive worse and you won’t actually be saving money with your reduced milage. Unless it’s an emergency and you have no choice, get the recommended.
Octane is basically irrelevant to the issue of ethanol. The relevant issue is that gasoline (ethanol-free) has a specific energy of 47.3 MJ/kg, while ethanol has a specific energy of 29.7 MJ/kg. You need 1.6 gallons of ethanol to get the same energy as a gallon of gasoline.
I don’t think there is a regular 85 octane lowest in Nebraska is 87 octane. E85 is the ethanol version but your vehicle has to be able to use it.
Some 87 here can have small amounts of ethanol if it says so at the pump and that can be used in normal vehicles. Older cars pre2000 don’t run well with it and some with carburators can get vapor lock
I’m a car girl, its mkind of my thing. Octane ratings aretgere to protect your engine, its a rating of how readily the gasoline ignites in the engine. The larger the number the harder to self ignite. Most cars use 85, the only time the higher octane 93 is needed is for cars with turbo or supercharging, or cars with higher compression ratios.
Just put whatever its rated for in it, going with a higher octane than what your car is rated for doesn’t hurt a thing, but it also won’t make your engine run better or anything.
As far as ethanol goes, modern cars ate fine with 10-20% ethanol in their gas. It will get worse mileage the higher the percentage of ethanol as it is not as energy dense as gasoline. The E85 stuff has a higher percentage of ethanol (85%) than is allowed in conventional gas and was introduced to try and lower gas prices (it’s actually completely ineffective and ethanol for fuel is more energy intensive than just giving us straight gasoline but they have to prop up the corn industry somehow). Regular cars can’t use E85 unless they are rated for it as the engine has to add more fuel to keep a close to stoichiometric ratio of fuel to air.
TLDR: Use whatever octane your car asks for, if you put a higher octane in it doesn’t hurt, but it also doesn’t add any benefit.
When it comes to ethanol regular cars can tolerate up to roughly 20% with only a reduction in fuel mileage as a result. E85 is only for cars rated to use it as they need a sensor to detect ethanol percentage and adjust fuel to air ratios accordingly.
Okay so to quickly summarise: the octane number defines just how explosive the fuel is under compression. 100 means it’s the equivalent of a 100% iso-octane mixture.
The more explosive the fuel is, the sooner it detonates as the cylinder compresses it. If it detonates too soon, at too low a compression, that’s when your engine starts to knock. By adding ethanol you’re increasing the pressure needed for detonation, ensuring that the ignition system ignites the fuel at the appropriate time, thus improve the engine’s longevity.
When you expect more (bam bam), from a litre.