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Default Mixing E85 and Pump Gas? Wait a few minutes! Literally. - 10-19-2016, 08:13 AM

I've spent the past few years mixing E85 and 93 octane at the pump in both my 535i and 135i. As soon as I started doing this, I always wondered exactly how long to let things mix before getting deep into the throttle. I naturally sway towards the safe side, so I'd always wait 5-10 minutes before assuming the ratios were consistent in the tank.

After recently installing Fuel-It's upgraded fuel lines, ethanol sensor, and ethanol analyzer, I've been able to have a live view of how much ethanol is actually running into my engine. Now that I've filled up a few times with the new equipment, I've kept a close eye.

From almost completely empty (around 1/16th of a tank of E40 remaining -- confirmed using the ethanol analyzer), I added 7 gallons of 93 octane. For almost 2 full minutes (over a mile of driving), the sensor detected E40 before finally dropping and settling to somewhere around E13. Once I'd made it to my E85 station, I topped off the tank.

Again, it took almost 2 full minutes of light driving for the sensor to start detecting the increased ethanol content before settling again around E40.

So the moral of the story is, if you have previously been running a straight pump gas, and then add a few gallons of E85, 2 minutes of light driving, perhaps a little less if moderate driving, seems to be the point in which you're getting the updated ethanol ratios to your engine. I just wouldn't recommend going WOT straight out of the station relying on the fuels to already be mixed as soon as they hit your tank.


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Last edited by chadillac2000; 10-19-2016 at 04:19 PM..
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J.J4ck0wsk1 J.J4ck0wsk1 is offline
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Default 10-19-2016, 09:38 AM

Damn good thread I've always wondered the same thing, I figured after five minutes or so you should be good. Glad you confirmed it takes about half that time. It's always so tempting to hit it right out the gate, but you've gotta wait.. I also wonder how long it takes the sensor to start displaying the correct value, is it fairly instantaneous?
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Stucks Stucks is offline
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Default 10-19-2016, 09:43 AM

Shiv did testing years ago and concluded it takes about 7 minutes to start mixing in the tank when you fill with regular pump gas and e85. After an additional 2.5 minutes, fuel had mixed. so around 10 mins total.


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J.J4ck0wsk1 J.J4ck0wsk1 is offline
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Default 10-19-2016, 09:47 AM

Yeah, but the sensor on the OP's car isn't going to lie so once the mixture is correct you are good to go. Besides if the mixture isn't correct won't the dme pull timing and keep the motor safe while the car making a little less power be the only side affect for the time being..
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Default 10-19-2016, 10:54 AM

Quote:
Originally Posted by J.J4ck0wsk1
Damn good thread I've always wondered the same thing, I figured after five minutes or so you should be good. Glad you confirmed it takes about half that time. It's always so tempting to hit it right out the gate, but you've gotta wait.. I also wonder how long it takes the sensor to start displaying the correct value, is it fairly instantaneous?
Sensor stays at the pre fill up levels of ethanol for the 2 minutes or so, then starts working it's way towards the number it bottoms/tops out at over the next 15-30 seconds.

Quote:
Originally Posted by Stucks
Shiv did testing years ago and concluded it takes about 7 minutes to start mixing in the tank when you fill with regular pump gas and e85. After an additional 2.5 minutes, fuel had mixed. so around 10 mins total.
Quote:
Originally Posted by J.J4ck0wsk1
Yeah, but the sensor on the OP's car isn't going to lie so once the mixture is correct you are good to go. Besides if the mixture isn't correct won't the dme pull timing and keep the motor safe while the car making a little less power be the only side affect for the time being..
Better safe than sorry I suppose if you feel so inclined to wait the full 10 minutes, but as J.J4ck0wsk1 said, the proof is in the sensor reading. If the sensor is seeing the intended ethanol levels 2 minutes after adding the fuel, there's no reason to wait 8 more minutes.

The sensor is located fairly close to the HPFP, so it's not far behind at all on seeing what concentration the injectors are spraying -- which completely discredits the 7 minutes to start mixing in the tank argument.


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Last edited by chadillac2000; 10-19-2016 at 11:11 AM..
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J.J4ck0wsk1 J.J4ck0wsk1 is offline
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Default 10-19-2016, 11:43 AM

Now I'm wondering if that was just a static 7-10 minutes Shiv was talking about without driving lol.
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Torgus Torgus is offline
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Default 10-19-2016, 12:17 PM

Quote:
Originally Posted by Sirdaft1
I just swerve back and forth violently after filling up lol
This.


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Default 10-19-2016, 01:41 PM

Great info. I mix regularly so I appreciate the legwork you put in.


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YoungBlood YoungBlood is offline
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Default 10-19-2016, 01:58 PM

Cool! Good to know


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N54QC N54QC is offline
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Default 10-19-2016, 03:14 PM

Been seriously kicking around the idea for the past couple of weeks about getting the sensor because I always wondered the same thing. Glad you posted, great info.


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Default 10-19-2016, 03:35 PM

Quote:
Originally Posted by Torgus
This.
Yes, this lol.

"Sorry officer, I was mixing my fuel"


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viperware viperware is offline
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Default 10-19-2016, 04:44 PM

You should put the E85 in first and then put the pump gas on top of it. It will mix quicker that way.


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Default 10-19-2016, 04:47 PM

Quote:
Originally Posted by viperware
You should put the E85 in first and then put the pump gas on top of it. It will mix quicker that way.
Won't make a lick of difference as far as getting the intended ratios into the injectors. Maybe if you completely ran out of fuel and somehow got everything out of the lines.


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Last edited by chadillac2000; 10-19-2016 at 04:53 PM..
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viperware viperware is offline
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Default 10-19-2016, 05:02 PM

Quote:
Originally Posted by chadillac2000
Won't make a lick of difference as far as getting the intended ratios into the injectors. Maybe if you completely ran out of fuel and somehow got everything out of the lines.
You put more pump gas in than E85 right? More turbulence = more mixing. Won't work for people with bad fill up patterns.


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Steve @ BMS/Fuel-It! Steve @ BMS/Fuel-It! is offline
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Default 10-19-2016, 05:28 PM

Fuel is constantly circulating with the jet pumps, return, and transfer from the driver's side. It mixes very quickly. It's mostly the fuel in the lines that you have to consume prior to your sensor reading the new ethanol content. At idle you use very little fuel.



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Default 10-19-2016, 07:59 PM

Quote:
Originally Posted by Steve @ BMS/Fuel-It!
Fuel is constantly circulating with the jet pumps, return, and transfer from the driver's side. It mixes very quickly. It's mostly the fuel in the lines that you have to consume prior to your sensor reading the new ethanol content. At idle you use very little fuel.
Thanks for chiming in on that aspect. So for the swervers in here (I used to be one as well), sounds like that is not necessary!


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Default 10-19-2016, 09:17 PM

Correct...



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E90Ryan E90Ryan is offline
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Default 10-20-2016, 06:14 AM

Thanks for clarifying this, I never understood why 10 minutes was tossed around, waiting for the burgers to cook?
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