Best octane fuel for fuel eceonomy? (5.3L only)

[BG1988]

Trying to get better mileage by switching octane is a fool's errand.

The octane rating does not change the amount of energy in a gallon of gas. The octane rating is merely a quantifiable measure of how fast the fuel burns. Higher octane burns slower.

Any purported "increase" in mileage using a higher octane is easily offset by the higher cost, negating the benefit.

Never mind the fact that these things were/are built for a myriad of reasons, the least of which is economical use of fuel. Giant vehicle, horrible aerodynamics, large V8 engine. You want good mileage? Buy a Prius.

depends I can get 22.5/26MPG on 91 octane and 18.5/18.5 on 87 octane

2.99/gallon =0.162 cents a mile
3.29/gallon =0.146 cents a mile

so at 2.99 i'll be spending $0.729 more to go 22.5 miles city
so at 2.99 i'll be spending $1.222 more to go 26 miles highway

so at highway speeds i get a range of 637 miles

net savings: 0.43/0.922 per gallon
sounds like a good deal to save a dollar per gallon

 

[91RS]

But that's with a hybrid and a 6.0L.

 

[wjburken]

But that's with a hybrid and a 6.0L.

Details! Brent always fails to mention that little tidbit when he shares MPG stories.

 

[thompsoj22]

depends I can get 22.5/26MPG on 91 octane and 18.5/18.5 on 87 octane

2.99/gallon =0.162 cents a mile
3.29/gallon =0.146 cents a mile

so at 2.99 i'll be spending $0.729 more to go 22.5 miles city
so at 2.99 i'll be spending $1.222 more to go 26 miles highway

so at highway speeds i get a range of 637 miles

net savings: 0.43/0.922 per gallon
sounds like a good deal to save a dollar per gallon

To be able to drive a full size suv with those mpg numbers is really a great benefit of hybrid ownership. If you were to amortize the per mile replacement cost of new OEM back seat batteries every 7 to 10 years how would that affect your per mile numbers? Also, I know you have one gas engine but how many electric motors? Add the replacement cost of the electric motors also to your amortization. Im not hacking but the "complexity/weight/maintanance cost's" that you endure to get those "best case scenario" numbers isnt without the financial burden of owning/maintaining a hybrid? And the resale of all hybrids tanks after the first owner.

 

[intheburbs]

depends I can get 22.5/26MPG on 91 octane and 18.5/18.5 on 87 octane

2.99/gallon =0.162 cents a mile
3.29/gallon =0.146 cents a mile

so at 2.99 i'll be spending $0.729 more to go 22.5 miles city
so at 2.99 i'll be spending $1.222 more to go 26 miles highway

so at highway speeds i get a range of 637 miles

net savings: 0.43/0.922 per gallon
sounds like a good deal to save a dollar per gallon

Nope, not buying it. Other factors are involved. Maybe the premium has a lower ethanol content.

The Federal government, Consumer Reports, and just about the rest of the planet all agree that switching octane has no measurable impact on mileage.

Next time I'm in the Rockies coming down from one of the Divide passes, I'll reset my mileage computer at the top, and then brag about how I got 73 MPG in my 6500-lb truck.

 

[iamdub]

When mine was stock, I got around 2 MPG more running 93. I ran that because it'd knock under hard load during hot weather running 87. There was nothing wrong with mine, this is normal for these and is why Black Bear recommends 89 or higher. I only use Chevron, Texaco, or Exxon. The extra MPG wasn't directly from the higher octane. It was because the lower octane caused knock, which made the PCM retard the timing which decreased the power/efficiency.

I now average 23 MPG, cruising at 70 MPH with the mods in my sig (cammed, raised compression, tighter quench, NO AFM). My previous best was 22 MPG at 70 MPH way back when I had AFM.

 

[Quark]

I have a 2012 Tahoe 5.3 L engine pure stock with 35,000 miles.

I've switched back and forth using 87 and 89 octane comparing mileage on trips, city has too many variables so I don't look at that as a guide. Without keeping logs but trying to be objective, over many trips and spanning many years, I see at least 1 mpg advantage to 89 octane over 87 sometimes maybe 2 mpg. Trips usually get from a low of 19 mpg to a high of 23 mpg depending on hills, wind, tire pressure and load with the high range entirely using 89. Plus the engine goes to 4 cylinder mode more often with the higher octane, this I'm sure of.

I try to stick with Marathon and Mobil the latter being my preference. When using Mobil 87 octane results are close to Marathon 89 octane though not quite. I also compare how smoothly the engine accelerates and idles with these brands and octane. In our area if one shops around 89 octane is about 30 cents higher at present and in my opinion the advantage in mileage and performance mostly offset the higher cost. When I'm on the road the difference in cost is greater then I'll use 87 and watching instant mileage I can see it fall after a few miles and acceleration suffers a bit.

I'm entirely aware of the argument concerning the energy content of 87 and 89 octane being equal but go with the idea that 89 in these engines allow them to use that fuel more efficiently. For my money I prefer spending a bit more and enjoying the ride I get, after all, it is a small increase at most and one of the reasons I drive the Tahoe is enjoyment.

 

[swathdiver]

I have a 2012 Tahoe 5.3 L engine pure stock with 35,000 miles.

I've switched back and forth using 87 and 89 octane comparing mileage on trips, city has too many variables so I don't look at that as a guide. Without keeping logs but trying to be objective, over many trips and spanning many years, I see at least 1 mpg advantage to 89 octane over 87 sometimes maybe 2 mpg. Trips usually get from a low of 19 mpg to a high of 23 mpg depending on hills, wind, tire pressure and load with the high range entirely using 89. Plus the engine goes to 4 cylinder mode more often with the higher octane, this I'm sure of.

I try to stick with Marathon and Mobil the latter being my preference. When using Mobil 87 octane results are close to Marathon 89 octane though not quite. I also compare how smoothly the engine accelerates and idles with these brands and octane. In our area if one shops around 89 octane is about 30 cents higher at present and in my opinion the advantage in mileage and performance mostly offset the higher cost. When I'm on the road the difference in cost is greater then I'll use 87 and watching instant mileage I can see it fall after a few miles and acceleration suffers a bit.

I'm entirely aware of the argument concerning the energy content of 87 and 89 octane being equal but go with the idea that 89 in these engines allow them to use that fuel more efficiently. For my money I prefer spending a bit more and enjoying the ride I get, after all, it is a small increase at most and one of the reasons I drive the Tahoe is enjoyment.

Jake, just wait until you feed it a mix of ethanol and then see how it performs!

 

[Quark]

James, I'm curious as I've only used it once and don't remember how it affected things. I live in a small market and worry that the ethanol isn't fresh so I haven't used it since. Do you mind telling us what you like, mileage, performance, cost?

 

[swathdiver]

James, I'm curious as I've only used it once and don't remember how it affected things. I live in a small market and worry that the ethanol isn't fresh so I haven't used it since. Do you mind telling us what you like, mileage, performance, cost?

Well, I like my fuel to deliver the most horsepower, the best gas mileage at the least possible cost!

Full strength E85 is great, engine runs cooler, smoother, shifts better even and makes more power. I've never intentionally ran 87 or anything less than 93 in my vehicles.

Last year we burned 21 tanks of 93 with an alcohol level of 10% or less. Truck averaged 15.5 MPG which cost an average of nineteen cents a mile to drive.

Burning mixes of 87 or 93 or E15 with E85 with an alcohol content of between 11% and 20% also delivered an average of 15.5 MPG which cost an average of seventeen cents a mile to drive.

Same mix but with an alcohol content of between 21% to 30% cost the same but delivered 14.8 MPG.

E85 was cheap last year and the truck averaged fifteen cents a mile with 12.4 MPG.

Our DICs let us calculate all kinds of data and efficiencies:





PPG = Price per Gallon
CPM = Cost per Mile
MPG = Miles per Gallon
GPH = Gallons per Hour
MPH = Miles per Hour
AC% = Alcohol Content Percentage