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Close to pulling the trigger on e30

6133 Views 53 Replies 13 Participants Last post by  JaBoogedy
Like the title states, oh so very close. I live in Iowa so (obviously) e85 is everywhere. My only real hesitations are economy and testing, this being my daily driver. Basically how much milage should I expect to be sacrificed to the corn gods when just driving it normally and should I be testing the e85 on every fill-up? I see you can get a gauge but it doesn't seem like most people do that.

Edit: finally came across the "Calling all e30 tunes" thread. I feel like this is a must read for anyone considering ethanol, a TON of good info in there. Hopefully this isn't a dumb question, would there be any harm in filling up 30 gals (I have 36 gal tank) and using a gauge to check the ethanol content, using the last 6 gallons to correct if necessary? I don't know why I am so against testing 馃槄
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Frequently Asked Questions (FAQs) - U.S. Energy Information Administration (EIA) says "The energy content of ethanol is about 33% less than pure gasoline."

For E10: 0.9 * 1 + 0.1 * 0.67 = 0.967 of pure gasoline
For E30: 0.7 * 1 + 0.3 * 0.67 = 0.901 of pure gasoline

(0.901 - 0.967) / 0.967 = -0.068

Expect 6.8% poorer MPG with E30 vs E10.

Agree with the admonition to test for ethanol content. Friends tell me E85 never has 85%. That by law it can be 70% but in practice it can be much less.
Octane-rating (AKI, not "octane") mixes linearly same as the equations I posted earlier.

Lets assume E10 and E85 really are 10% and 85%. Correct the numbers based on your test results.

I don't see AKI listed on E85 pumps around here but most references say 104 AKI if it really is 85%. It might be 100 AKI for lesser proof.

To mix E10 and E85 for E30:

0.9 gasoline + 0.1 ethanol + X * ( 0.15 gasoline + 0.85 ethanol ) = ( 1 + X ) * (0.70 gasoline + 0.30 ethanol)

After much fun math: add 0.364 gallons of E85 to 1.0 gallons of E10 to make E30.

A = 0.90 for 90% gasoline in E10
B = 0.15 for 15% gasoline in E85
C = 0.70 for 70% gasoline in E30

( A - C ) / ( C - B ) = ( 0.90 - 0.70 ) / ( 0.70 - 0.15 ) = 0.363636363636364

1.0 gallons of 87 AKI plus 0.364 gallons of 104 AKI E85:
(1.0 * 87 + 0.364 * 104) / ( 1.0 + 0.364 ) = 91.5 AKI

Some say E100 is 107 AKI and 85 AKI is the base gasoline used. That produces 87.2 AKI for E10, 103.7 AKI for E85, 91.6 AKI for E30.

87 AKI E10 needs 84.7 AKI E0
89 AKI E10 needs 87.0 AKI E0
91 AKI E10 needs 89.2 AKI E0
93 AKI E10 needs 91.4 AKI E0
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I know positive OAR is bad, stock tunes can have it.... how much positive is acceptable and where do you start to worry?
If it is not running bad and MPG reasonable don鈥檛 worry about it. However one should note the source and consider others if one can get lower and negative numbers for same price. I鈥檓 getting 22 MPG around town on +0.25 OAR. Have a 130 mile day coming up. Not going to pass judgement until the engine has an honest chance to calibrate this fuel.
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In the OBDLink app I had to manually add the PID for OAR. Don't remember what I did other than enter the numbers then select a "gauge" to display the value. Set the display range to -1 to +1 as it defaulted to -1000 +1000.

I the math post above, late at night, the main equation is correct but needlessly complicated by including both gasoline and ethanol in one. Easier to solve for mixing 90% gasoline with 15% gasoline to get a 70% mixture. Or you will get the same answer mixing 10% ethanol with 85% ethanol to get a 30% ethanol mixture. The gasoline one is the A, B, C, equation.
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