Does anyone have personal experience with E85 "Flex Fuel"? I did a search which turned up a lot about ethanol production but very little on the subject of engine performance.
I bought gas at Sheetz this morning and noticed E85 (85% ethanol) was around a buck per gallon cheaper than regular E88 unleaded (15% ethanol). E85 has always been cheaper but I've never seen this big a difference before. I suppose it makes sense since the price of ethanol doesn't necessarily keep pace with the price of oil.
My 2012 GMC pickup burns E85 Flex Fuel. I kept careful mileage records and found it almost a wash as to which fuel was more economical. I used the E85 mostly because it was the "green" thing to do or so I thought, but I didn't care for the loss of mileage & performance.
I don't want to start an endless debate on the environmental impact of ethanol. Instead, I'd like to hear from others about how well E85 performs in your equipment. I'm considering a new vehicle and I'm trying to decide if it's worth buying another that uses flex fuel.
Yep, I've burned thousands of gallons of the stuff. I live in the Midwest and E85 is less expensive than 87 octane gasoline and at the present time, it's $1.00/gallon less than the 87 octane which has 10% ethanol. My truck can technically run on 87 octane regular but isn't happy doing so, particularly when towing, it will ping pretty noticeably. Most of the pinging when towing goes away with running 91 octane premium that's 90 cents/gallon more than regular unleaded, and E85 makes it completely go away no matter what.
The only issue with E85 is that its vapor pressure is a bit low to reliably fire right off on a cold start when it is below zero. It very rarely gets that cold here but I've been places where it has been that cold. I stuck to no more than 30% ethanol when it got below zero and had no problems starting despite it getting to -40 F during a cold snap.
I learned recently you can get by running lower octane at higher elevations, hence why you only see in it places like Colorado.
That was true for carbureted naturally-aspirated engines that have no ability to change timing or air-fuel ratios at a given throttle position and engine load. There are fewer molecules in the intake air at high elevations and thus there is less cylinder pressure at top dead center, just as if you had a lower compression ratio, and is why you can run less octane. The ASTM figures are that you can decrease octane by about 1.0-1.5 points for every 1000 feet above sea level.
This is less true for closed-loop naturally-aspirated EFI engines that can change timing and air-fuel ratios on the fly, you can run lower octane but it's much smaller of a difference relative to sea level vs. a carbed engine. The SAE's figures are that you can decrease octane about 1 point for every 5000 feet above sea level in a closed-loop EFI naturally-aspirated engine.
It is absolutely NOT true for turbocharged engines where the turbocharger will stuff the same amount of oxygen into the cylinder at higher elevations as at sea level up to at least 10,000 feet or so above sea level, and maybe higher, depending on the specific engine.
I never lived in Colorado but I did live in South Dakota in the past. 85 octane gas was sold in the western part of the state at elevations of roughly 5000 feet above sea level and higher. That old carbed car that was specified to run on 87 at sea level would do fine on the 85 octane stuff as long as you didn't drive below 1500-2000 feet above sea level, which meant you were fine until you drove more than about 250 miles or so to the east. An EFI car specified for 87 at sea level would be below the recommended octane on 85 unless you were 10,000 feet above sea level or higher. A turbocharged engine would be hurting as most today are designed for 91+ octane and are pulling a significant amount of boost and timing to even run on 87 in the first place. Any owners' manual I have ever had for an EFI car has specifically stated to abide by the listed octane requirements regardless of altitude, and that would be why.
