Fuel octane and mileage for 2008 M35x.

[gsmollin]

I have been doing a fuel octane vs mileage study on my 2008 M35x. Results, so far, are like this:

Octane 93 91 89mpg 17.6 18.7 18.6

The most surprising result is the drop-off in mpg with 93 octane. I expected the results at 89 to be close to 91.

Driving has all been commuting to work, which is a mix of highway and suburban roads over a consistent distance of 25 miles between starts.

I'm wondering if anybody else has tried this, and what are the results.

[M45Runner]

I have tried on M45 and it seems that I get more mileage on 91 than 93 - like 18.7 with 91 vs. 18.4 with 93. So, I am stick with 91 for now

FYI, 89 is not an option for M45. Although I did used it once before due to availability and the car does feels slower, although the mileage is the same as when using 91 - 18.7MPG.

[NightWatch]

My driving is similar to yours, although maybe a bit more miles - 28. I use 93 all the time and I get 19.9 MPG consistently. My surprise had more to do with the minimal change between Hiway driving and my Hiway/surburban mix commuting. I only get about 22.8 MPG on the Hiway at 65 - 70 MPH

[gsmollin]

19.9 is darn good mileage. Do you have the 7 speed transmission in your M35? Your commute may be more highway than mine. Of course, my cruisin' at 80 on the PA Turnpike gives lower mpg than 65... at least that's what I heard.

Perhaps I'll run through a few more tankfuls of 93 to see if the mpg is higher now than it was in February, when I started this study.
Modified by gsmollin at 11:17 AM 6/4/2009

[NightWatch]

Actually my commute on the hiway part of the trip (about 20 miles) I end up hitting the brakes more often and go and slower MPG (probably averages about 35 MPH) than the suburban part of the trip where I average about 45 MPH and only have to stop at lights.

[EniGmA1987]

I dont have any real numbers cause I didnt do a full to empty test, I just put in $20 to test out how the car does with 89 fuel. But I can see from how fast the gas is going down that the 89 fuel gets way worse milage than 91 does for me. I have been driving less on the weekend than during the week and it is going down on my gauge twice as fast. The power difference is also susbtantial, especially around the 90mph range. Where I live we have 91, 89, and 87. And I will never be buying 89 or 87 again.

[M45Runner]

My surprise had more to do with the minimal change between Hiway driving and my Hiway/surburban mix commuting. I only get about 22.8 MPG on the Hiway at 65 - 70 MPH

I found this to be true as well - It could be caused by the gearing. The best I have got on highway is 23.5 (after warm up and cruise around 70).