Originally Posted by WobblyElvis
Doing the math, E15 has %95 of the energy that straight gasoline has so on the highway you might lose 2 mpg. With E10 you are already losing about 1.2 mpg vs gasoline. Looks to me that E10 or E15 is a slightly better buy in most cases but if it leads to mechanical problems it would not be worth it.
Here's more math:
The following is the true gasoline octane ratings with various ethanol levels in ethanol blends.
First, 87 octane 100% ethanol-free gasoline (E0) is octane 87. Duh!!
Second, inaccurate, but "designated" 87 octane 10% ethanol-blend (E10) has its gasoline component at 84 octane.
Third, inaccurate, but "designated" 88 octane 15% ethanol-blend (E15) has its gasoline component at 83.5 octane.
Fourth, inaccurate, but "designated" 87 octane 15% ethanol-blend(E15) has its gasoline component at 82.4 octane.
Only 87 octane E0 has its gasoline at 87 octane & has the best MPG, as prescribed by 87 octane gasoline engine engineers. No 87 octane ethanol-blend has any of its gasoline components anywhere near 87 octane. In my five 87 octane, low-compression ratio gasoline engines, 87 octane E0 gains 8%, 8%, 7%- 8%, 7%, & 5% better MPG, over inaccurate, but "designated" 87 octane ethanol-blend E10.
The "ethanol in gasoline industry" has bribed the public to dilute our nation's gasoline stocks with inaccurate, but "designated" 87 octane E10. Now, the "ethanol in gasoline industry" will dilute our gasoline stocks further by pushing 88 octane 15% ethanol blend to the public. If successful, the "ethanol in gasoline industry will dilute our nation's gasoline stocks further with 87 octane 15% ethanol blend.