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

 

[Quark]

I'm envious of your meticulous record keeping.

I see that Marathon and Shell have the lowest CPM with $ 0.16 and have an average ethanol content of 73% and 78%. That's interesting. Another thing is that your MPG is much lower than what I normally get, city 16-18 and highway 19-23. I drive conservatively and don't let the Hoe idle any more than necessary. I will try E-85 one of these days to get a comparison.

 

[swathdiver]

I'm envious of your meticulous record keeping.

I see that Marathon and Shell have the lowest CPM with $ 0.16 and have an average ethanol content of 73% and 78%. That's interesting. Another thing is that your MPG is much lower than what I normally get, city 16-18 and highway 19-23. I drive conservatively and don't let the Hoe idle any more than necessary. I will try E-85 one of these days to get a comparison.

Marathon and Shell were one time fill ups each. The Shell stop was basically all highway, an airport run to help out some stranded travelers one Christmas.

Jake, my rig is an XL 4x4 with 3.42 gears and all-terrain tires. The motor is pre-VVT which is good for a solid mpg, the motor was tuned by BlackBear and AFM is turned off. The best highway mpg this truck has ever seen was 19.1 MPG and climbing on E25 (18 gallons E15 and 8 gallons E85) on an airport run after about two hours. Unfortunately, she was nowhere near that on the way back! This thing never leaves the driveway weighing less than 6300 pounds.

 

[cfmistry]

Well gentlemen I have enjoyed reading this thread and its responses, and I hope it continues. While a few of you dispute any changes to fuel economy when increasing octane, most people who have actually done it report an increase. To me 1-2mpg consistent improvement is fantastic.

I have averaged 13.2 mpg (mixed highway/city) over the past 1000mi. My truck has 22" aftermarket wheels (tires at 38psi) and a Range AFM module but is otherwise bone stock. For the next 1000mi I will run only 93-octane and report back. Then finally I will try 89-octane.

As stated before, I am doing this more for increased range rather than the increased fuel economy itself. The cost is irrelevant to me.

 

[wjburken]

The problem I have is around me, if I get 87 octane, it’s 10% ethanol, 89 octane is 15% ethanol. I have to go to 91 octane to get to non-ethanol or go to E85 and get anywhere from 55% to 80% ethanol. Hard to get a straight comparison for just octane without ethanol content coming into play.

 

[BG1988]

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.

to break it down quickly it saves $2,500 per 14,000 miles driven Compared to the typical MPG of a 6.0L (10/13mpg) engine in a 1500hd/2500 series

so the average battery last 140,000 miles

10*2,500 = $25,000 saved for each battery on gas

so the battery will pay for it self in fuel savings at 28-30,000 miles of highway use. 36-38k in city use


these are built pretty solid it uses a $10,000 BUS transmission after all(the early production) they are rated for 300,000+ miles of use.. and they run pretty cool 150F -175 (in the summer) the engine normally is barely spinning at 1000-1500rpm is typical


each unit cost GM $90,000 to build so they took a pretty steep loss on each of them... most of the losses was from the design revision basically did a mid year refresh to the front and rear of it.
(some design elements carried over to k2xx..)
it has enhanced AFM (you can accelerate/decelerate in v4 mode), Enhanced DFCO and VVT..Variable-displacement oil pump, ( even though GM claimed it was first introduced in the corvette in 2014 C7) that is how you are able to squeeze every mile out of it..

 

[R Black]

Octane and the amount of energy in the fuel are two different things in my opinion. If I am not mistaken, Octane indicates how resistant the fuel is to premature detonation due to compression which is why the higher the Octane is, the less pinging you get. This is why higher compression motors, like the 6.2, need higher octane fuel. There is a small correlation between octane an mpg, but if you put 93 octane in a motor designed to run 87 octane, you won’t see a big change in mpg’s.

Typically, you will get better mileage with a furl that has less alcohol, but more power with more alcohol.

@swathdiver has a thread where he discusses this at length.
https://www.tahoeyukonforum.com/threads/useless-information.97483/page-85#post-1456757

I would concur. The less alcohol the better the mpg. I believe the 'no greater than 15%' rule still applies to the Gasoline Norm Aspirtd. 5.3 for 2020 ( a long standing 'rule') However I think I do remember that the Owners manual contains a recomm. for 'Top Tier' gasoline only, if memory serves, and it has it's own little logo thinghee to make it thuper speshal and give it brand recognition. The octane recomm., for the 5.3, I believe is 87 or higher as noted by another member.

I think you may have made a typo there though. getting better mileage from a gallon of fuel also means you are getting more power from that gallon of fuel.

 

[brichter]

these are built pretty solid it uses a $10,000 BUS transmission after all(the early production) they are rated for 300,000+ miles of use.. and they run pretty cool 150F -175 (in the summer) the engine normally is barely spinning at 1000-1500rpm is typical

Bus transmission? What trans is that?

 

[wjburken]

Bus transmission? What trans is that?

They have a Electronically Variable Transmission which is a a version of a CVT.

 

[George B]

Just filled up with 21 gallons of 91-E0 at 2.899/Gal. I will need to get an average of 17.5 MPG in order to break even on the difference in cost over 87-E15.

I am averaging 13.4 currently on 87-E15 with a mix of city and highway driving.

I am skeptical that I will see that increase in MPG but we will see.

 

[donjetman]

Octane and the amount of energy in the fuel are two different things in my opinion. If I am not mistaken, Octane indicates how resistant the fuel is to premature detonation due to compression which is why the higher the Octane is, the less pinging you get. This is why higher compression motors, like the 6.2, need higher octane fuel. There is a small correlation between octane an mpg, but if you put 93 octane in a motor designed to run 87 octane, you won’t see a big change in mpg’s.

Typically, you will get better mileage with a furl that has less alcohol, but more power with more alcohol.

@swathdiver has a thread where he discusses this at length.
https://www.tahoeyukonforum.com/threads/useless-information.97483/page-85#post-1456757

Octane is about detonation and pre-ignition prevention, not about energy per gallon.

Example: Methonal has about half the BTUs(energy) per gallon of Gasoline. Methanol naturally has a very high octane rating even though it has half the energy.