MPG at different octanes

[Ibex]

Okay this is mainly for an observation of mpg and using different gas stations over an extended trip. I went on a road trip from Austin, Tx to Des Moines, Ia and covered 2200 miles round trip using mainly I35. The terrain over varies slightly mostly flat with rolling low hills. The truck is a 2014 silverado z71 4x4 5.3 w the 3.4 (the middle one) rear end. I had an RC 2.5 level installed w 275/60/20 cooper zeons before the trip. At the first station I filled up w 87 octane from valero and got 14 mpg. At the next station (an exxon) I got 89 octane and it went up to 17 mpg. I was surprised and thought "okay this thing likes octane." At the next station I put 91 in and it went back down to 14. Now this is all highway. While in Iowa I drove around and didn't look at the numbers much cause I was showing off some for the brothers.(big grin) On the return trip I found another Exxon w 89 octane and jumped on it. Boom! Back up to 17 mpg. I filled up 6-8 times over the trip almost always filling the whole tank and the mpg seemed to vary quite a bit. Anyways that was my findings and I thought I would share. Averaged 15 mpg over the whole trip. The truck rode beautifully and I was completely comfortable. I really like it and I'm now looking for more Exxon stations to compare and see if it was a fluke.

[redwngr]

Maybe it likes exxon better than Valero.

[wandern]

Okay this is mainly for an observation of mpg and using different gas stations over an extended trip. I went on a road trip from Austin, Tx to Des Moines, Ia and covered 2200 miles round trip using mainly I35. The terrain over varies slightly mostly flat with rolling low hills. The truck is a 2014 silverado z71 4x4 5.3 w the 3.4 (the middle one) rear end. I had an RC 2.5 level installed w 275/65/20 cooper zeons before the trip. At the first station I filled up w 87 octane from valero and got 14 mpg. At the next station (an exxon) I got 89 octane and it went up to 17 mpg. I was surprised and thought "okay this thing likes octane." At the next station I put 91 in and it went back down to 14. Now this is all highway. While in Iowa I drove around and didn't look at the numbers much cause I was showing off some for the brothers.(big grin) On the return trip I found another Exxon w 89 octane and jumped on it. Boom! Back up to 17 mpg. I filled up 6-8 times over the trip almost always filling the whole tank and the mpg seemed to vary quite a bit. Anyways that was my findings and I thought I would share. Averaged 15 mpg over the whole trip. The truck rode beautifully and I was completely comfortable. I really like it and I'm now looking for more Exxon stations to compare and see if it was a fluke.

 

Did you notice the ethanol content of the different fuel grades?

[redwngr]

Did you notice the ethanol content of the different fuel grades?

Good point, especially since ethanol is an octane enhancer.

[Ibex]

I did. Almost all i came across say on the pump that it "contains up 10% ethanol." Also in Iowa, they offered two different 89 octanes at same store. One called unleaded and another called super unleaded and it had an ethanol sticker next to it and was 20 cents cheaper as well.

 

 

Sent from my iPhone using Tapatalk - now Free

[wandern]

I did. Almost all i came across say on the pump that it "contains up 10% ethanol." Also in Iowa, they offered two different 89 octanes at same store. One called unleaded and another called super unleaded and it had an ethanol sticker next to it and was 20 cents cheaper as well.

 

 

Sent from my iPhone using Tapatalk - now Free

 

Well, as the ethanol has lower energy density, you'll see your MPG decrease. A lot of times (especially in the midwest) I see the base ethanol-free 87 octane "enriched" with ethanol for 89 octane, and then 91 octane is again ethanol-free, which could be a contributory factor to your mpg findings.

[Cap'n Pete]

I'm curious to experiment with different fuels and see if it makes a difference. Here in Ontario, we've pretty much got exclusively ~10% ethanol fuel, except Shell 91, which is a zero octane fuel (pretty much the only one available anymore).

 

Unfortunately, I have a heavy foot, and do more city driving than highway, but will still be nice to see if either a higher octane fuel helps, or if the ethanol free fuel makes any difference.

[LS 1st Gen]

Speaking of ethanol, this new 5.3 will make about 30 extra Hp when you run the stuff.

[redwngr]

Speaking of ethanol, this new 5.3 will make about 30 extra Hp when you run the stuff.

What % ethanol is required for the higher rating?

[Cap'n Pete]

What % ethanol is required for the higher rating?

I don't think it gets the big jump unless you run E85 (85% ethanol).

[chewy22]

 

I don't think it gets the big jump unless you run E85 (85% ethanol).

From what I've read, believe you are correct. Take a big mileage hit with E85 too.

[chesterkv]

I was getting about 12mpg on E85. and when I use 87 I get about 16mpg, huge difference. Definitely feel the difference on power when running E85. The difference in cost ends up making you pay the same depending on where you live. E85 in my neighborhood is $2.99/Gallon, and 87 is $3.61/ Gallon.

[Tom's LTZ]

Here in Michigan we get E85 from Meijer and its $2.99 a gallon, 87 is currently 3.39. I only put about 12k miles per year so the lower gas mileage is not a big deal, I do have a heavy foot though so more ponies will be enjoyed for sure!

[fondupot]

I'd just attribute the difference in mileage to different ethanol contents. The truck is meant to drive on 87 octane, changing to higher octane really doesn't make a difference.

 

Pure gasoline will net better mileage when compared to gas with ethanol in it.

[nrbrandt]

Will e85 make the engine warm up faster in the winter since you're getting more HP? Probably not unless you're working the engine I imagine. Will a higher HP engine shift into V4 more often? Might gain a tiny fraction of an increase in MPG that way.