TL;DR
I got about 1MPG less in eco mode but might’ve been due to other factors such as weather that didn’t occur in normal and and idling for a bit longer
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Edit: 2018 Accord Touring 2.0T
Just went on a road trip about 600miles each way. I’ve seen so many conflicting things about whether the eco mode actually makes any difference on the highway or not so I decided to put it to the test myself on my most recent road trip.
Driving habits for this trip:
I tried to keep the driving habits relatively similar for this test as much as I could in my control. I tried to strictly use ACC and tried to keep the speeds set between 80-85 so lots of potential for increase and decrease in speed/rpms. Of course during some busier city sections, left lane hoggers, and passing people the speed fluctuated even more. Overall though I would say my average was 80-85MPH. On top of this I would get up to speed quickly on ramps on both modes.
Keep in mind this was not a test of highest efficiency but rather a VS between similar habits for both modes.
Initial results:
Normal Mode - 29.4
Eco Mode - 28.5
Yes that is right the ECO mode got about 1 MPG less but before jumping to conclusions that ECO is worse on the highway, I will give some more context as to why I think the results are the way they are.
As I stated earlier I tried to keep as much as I could the same however there were a few things I couldn’t control / were different from the Normal mode trip.
While In ECO mode the lowest mpg I hit was 27.4 but once the above driving/weather conditions let up and I was driving more and more since idling it crept up to the 28.5 that I recorded at the end.
Conclusion:
All in all if ECO mode does do anything on the highway, it is very minimal and doesn’t outweigh other factors such as environment. Additionally if eco mode is beneficial it may also not overpower a factor such as speed where at 85mph there’s not much work eco mode is really doing anymore.
I’m going on another trip within the next week that is about the same distance as this post and plan to do the same experiment but limiting my speed to 70-75, and trying to do other MPG highway saving techniques. Would you guys want to see a part 2 of those results?