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    Thread: Using E85 as an octane booster

    1. n00b
      Join Date
      Sep 3rd, 2019
      Location
      Richardson, TX
      Posts
      3
      Vehicles
      2016 Tiguan 2.0 TSI
      09-10-2019 10:14 PM #1
      New member, first post. So, I have a new (to me) stock (for now) 2016 Tiguan and a convenient gas station nearby that has 87, 89, 91 and E85, all at the same pump (diesel too, but that is for my other VW). Compared to a full tank of 91, 12 gallons of 87 and 4 gallons of E85 yields 91.5 octane and is about $15 less per tank. The $15 aside, what are the +/- implications of taking advantage of the savings? Thanks in advance for your response/s. DN.

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    3. 09-10-2019 10:17 PM #2
      Alcohol dries out snd raises hell certain materials in fuel system.

      Im sure fuel maps might been to be modified.

      It'll burn regardless.

    4. Member
      Join Date
      Sep 5th, 2015
      Posts
      387
      Vehicles
      '14 Grand Cherokee Overland, '09 Tiguan SE, '09 Tiguan SEL 4motion, '03 Boxster S, '82 quattro 20V
      09-10-2019 10:51 PM #3
      You cannot run an engine on E85 that was not tuned for it. Some of the Audi 2L TSI turbos are Flex Fuel and have an alcohol content sensor (as well as other components) that adjusts the fuel injection for the lower energy content of ethanol, which requires a much riches fuel/air mixture. No VWs got this engine (at least not in this country). These engines can be recognnized because they have aluminum intake manifolds and an extra injector. The Audi Flex Fuel 2L turbos can make a lot of power if properly tuned, but this is NOT something you can do on a VW CCTA engine as in our Tiguans.

      Bottom line, no you cannot run E85 in your Tiguan.

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    6. n00b
      Join Date
      Sep 3rd, 2019
      Location
      Richardson, TX
      Posts
      3
      Vehicles
      2016 Tiguan 2.0 TSI
      09-10-2019 11:01 PM #4
      Quote Originally Posted by Qmulus View Post
      You cannot run an engine on E85 that was not tuned for it. Some of the Audi 2L TSI turbos are Flex Fuel and have an alcohol content sensor (as well as other components) that adjusts the fuel injection for the lower energy content of ethanol, which requires a much riches fuel/air mixture. No VWs got this engine (at least not in this country). These engines can be recognnized because they have aluminum intake manifolds and an extra injector. The Audi Flex Fuel 2L turbos can make a lot of power if properly tuned, but this is NOT something you can do on a VW CCTA engine as in our Tiguans.

      Bottom line, no you cannot run E85 in your Tiguan.
      So even as an additive at 20%, your thoughts are that it is taboo? DN.

    7. Member
      Join Date
      Sep 5th, 2015
      Posts
      387
      Vehicles
      '14 Grand Cherokee Overland, '09 Tiguan SE, '09 Tiguan SEL 4motion, '03 Boxster S, '82 quattro 20V
      09-10-2019 11:48 PM #5
      Quote Originally Posted by NTPC4 View Post
      So even as an additive at 20%, your thoughts are that it is taboo? DN.
      I wouldn't...

    8. Member
      Join Date
      Apr 21st, 2008
      Location
      Southcoast, MA
      Posts
      7,332
      Vehicles
      Tiguan, Mini
      09-12-2019 07:37 PM #6
      I've had excellent luck doing this in SoCal with 91 and e85 in a Mazdaspeed Miata (factory turbo). On 91, in the summer / hotter temps, it ran rough and sluggish and obviously pulled timing all over the place. They're also woefully under-sized on the stock intercooler and I hadn't yet upgraded it. With 2.5gal of e85 poured before filling the tank with 91oct, I would beat the **** out of that car up and down Palomar Mtn and Ortega Hwy like it owed me money and rent was due. I separated the factory radiator and spewed coolant on one occasion and replaced that with a CSF b-core rad. Sorted that issue, and the days I was going for canyon runs I'd put 2-2.5gal e85 in there first.

      Now, having also owned the Tiguan in SoCal, I can't say that I would do the same. The tuning is better on these cars, and the ECU is much more workable. Even with a downpipe and stage 2 file, I never felt as though (admittedly on 93 at that time) it needed any more octane.

      Think gravel tumbler and resistance to rev vs sewing machine and being happy to be there.

      Sure it theoretically loses some power due to losing 6-7% BTU output, but the timing advance that remains and the decrease in combustion chamber temperatures compensate for that.

      I have no dyno maps, but I've gone faster than I'll post about in the Miata on different grades of fuel on an open interstate and up hot, winding canyon passes, and stand by the above.

      Edit: oh, as a consistent cost-saving measure - no. Buy a 2.5L Rabbit. If you're searching for a quick boost for 94-95oct, that's something the above should be used for...

    9. 09-17-2019 07:31 PM #7
      A friend of mine filled my tank with E85 by accident and service at my dealer said the cars are designed to take it and not to worry. Check first before using but that is what i was told.

    10. 09-17-2019 07:41 PM #8
      I ran a tank of e85 in a non ethanol 2019 passat.

      Eventually i got a check engine light. Still a screaming meany. I'm sure it wasn't the best for the fuel components...

      Emptied and full tank of normal spark fuel and it stayed off.


      Although!!!

      My 95 Chrysler voyager, cross referenced to the Brazilian market... Only difference was the ECU.......same orings, same pump, same injectors, same everything... Etc etc....


      Go figure.....?

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