Ethanol Mix Time

Part of having an Ethanol tune involves switching between the E30 tune and a straight 93 octane gas tune. In my case the 93 octane fuel is around 10% Ethanol from the pump and I have nearby (~30 minutes away) access to pump E85.

The Fuel-It Ethanol Content Analyzer has a companion application that allows some variables to be adjusted to help with filling up with each type of fuel to try and reach a desired mixture ratio.

Fuel-It! Ethanol Content Analyzer App
Fuel-It! Ethanol Content Analyzer App

Using the Fuel-It analyzer 0-5v output to a data logger the transition from E10 to E30, and from E30 back to E10, is recorded to evaluate how this transition occurs. The following charts show the transition for a few cases:

E30 to 93 Transition
E30 to 93 Transition

93 to E60 Transition
93 to E60 Transition

93 to E30 Transition
93 to E30 Transition

E13 to E26 Transition
E13 to E26 Transition

It takes a few minutes for the new mixture to make it from the gas tank to the sensor, and then a couple minutes more for the final mixture value to be reached.

My procedure is to switch the ECU tune to the mixture I plan to use (93 or E30), then drive the car to get the new mixture through the fuel system. Since there is a mismatch between the tune and mixture for the first few minutes I take it easy. Driving more aggressively would probably cause the new mixture to reach the sensor more quickly as more fuel in the fuel lines is being consumed.

Since the mix transition process is imprecise, takes some time, and the nearest ethanol supply station is not around the corner, I keep a small stock of E85 on hand to help with getting the mixture to the right percentage.

Fuel Containers
Fuel Containers

References:

2 thoughts on “Ethanol Mix Time”

  1. Chance Young

    What ethanol content are you mixing at and how many gallons? My 93 is also at 10% ethanol and I’m looking to see what I need to do e48-e50 on my GTI

    1. I use the Fuel-It app to calculate the percentages based on how much fuel I estimate to be remaining in the tank. Usually I don’t wait until the tank is nearly empty to fill up. I have a few containers of E85 in the garage so that I can make final adjustments as necessary to get right around 30% ethanol.

Leave a Reply

%d bloggers like this: