General Discussion

Can I use E85 in my MK7 GTI?

First and foremost our cars are not capable of handling straight E85 as is. Our fuel sensor is not designed to understand it and E85 can be more corrosive than regular gas. But it being more corrosive so far doesn’t seem to be an issue for our cars, I have heard very little about fuel lines degrading or other plastic parts/seals being an issue. To run straight E85 you need more than just a tune, you also need fueling upgrades for low-pressure fuel pumps and/or high-pressure fuel pumps, also multi-port injection (MPI) helps too. Check with your tuner first before upgrading, each tuner does it a little differently. Instead, it’s more common to blend/mix E85 with your current fuel to get something like E30 which typically doesn’t need fueling upgrades but you need to calculate constantly and really should have an E85 fuel sensor so you know what your current ethanol content is. E85 is also known as FlexFuel. E85 is “up to” 85% ethanol to gas. This depends highly on the brand on how far off it is, the average seems to be more like 72-79% for the average.  You can read up more in-depth on E85 here.

So let’s go over the benefits and downsides to using E85


  • Its better for the environment. Both in manufacturing and using.
  • Price, its typically a lot cheaper. For my area typically $1 a gallon cheaper over 91oct.
  • Burns cooler
  • Reduces knock, which is great for tunes
  • More performance!


  • Availability, my closest station is 15min away, so not ideal
  • MPG drops significantly. 
  • Can be corrosive
  • ECU has to adapt to take full performance advantage when switching fuel types

As you see there are some big benefits but also some downsides too. E85’s initial push was for being better for the environment, this is why current gas in the US typically has 10% ethanol in it already, or E10. So cars are already capable of handling a little ethanol in their fuel, this is why we can add a little more into the mixture without running into any issues. Mixing also helps reduce the corrosive issue as well as the MPG hit not being as bad. Mixing reduces a lot of the negative aspects of E85.

After a lot of experimenting it seems the consensus is that E30 is the right mixture for our cars unless you do fueling upgrades specifically for E85. You can find phone apps and web pages that help you calculate the correct mixtures to equal E30 or whatever percentage you want to run. I started out running something closer to E18 my first time, just to see what the fuss was about. Initially, I noticed nothing, the reason for this is your ECU (car’s computer) still needs to adapt to the new fuel and this can typically take 30 miles. For me this isn’t a big deal as my commute to work is 40 miles each way, but for those who don’t drive much, it can be annoying. After it adapted I did notice a bit of lower-end pickup when accelerating and my knock was reduced to nothing. My MPG was only down about 2mpg so not that bad.

Next tank I bumped it to E30 and wow that sure made a difference. Lots of low-end performance increase for sure, felt like 20HP gain but who can tell without a proper dyno test. Important to note my car is custom-tuned for 91oct. Needless to say, it was very noticeable after it adapted.  But now my MPG was down about 4-5mpg. The cost being a whole $1 cheaper than the 91 I was using I think offsets the MPG drop and ends up being a wash in the end. 

A bunch of folks on the forums are getting tunes especially for E30 and are reaping its benefits. This was temping but too inconvenient for me to get to an E85 pump. Due to the 15 minute drive to get E85 and in a direction, I never go, I won’t be running this all the time. But will surely add a splash to the tank whenever I pass by a station. 

It’s not uncommon for E85 pumps to not be full E85 and sometimes as low as E72. Make sure to test it, the same goes for what other fuel you are mixing with that’s rated UP TO E10 but might not be at E10. You can get test kits from Amazon. If you are tuned for a specific amount of E mixture and don’t mix close to that amount you could cause damage. Your calculations will change each time you fill up depending on your tank’s current amount of fuel and its ethanol content. It can get very complicated and too much guesswork for my liking.

This is why it’s highly suggested you don’t just calculate your fuel mixtures but get a proper ethanol sensor and gauge to read the E content of your fuel. Two kits seem to be popular one by Fuel-it and another by Innovate Motorsports. These both add a sensor to a fuel line that can read the E content. The Fuel-it model typically uses Bluetooth to a phone app to read it while the Innovate Motorsports uses a standard-looking gauge that you would mount somewhere in the cabin and run a line to. The driver’s side cubby seems to be commonplace to put this.

Update: EQT now has E30 Staged tunes now for the GTI and R, these are a cheaper alternative to custom tuning. I did pick one up for the occasional take of E30 on the weekend.