MPG tips

[OR VietVet]

I have used the 89 octane fuel since I bought my 2002 Tahoe with decent MPG results unless I am just doing in town stop and go driving. I decided to switch to 91 octane, premium, for this winter. I am completely surprised that I am doing way better on my MPG since I switched. I live where I work so unless I do get out on the interstate I do 95% driving in town. My rig just likes premium fuel way better, from Chevron.

 

[hardluck13]

91 isn’t going to give you better mpg. Didn’t see where you live but winter driving usually gives you better mpg (engine runs cooler, people including you driving slower etc....

higher the octane faster burn and so on.

 

[swathdiver]

I have used the 89 octane fuel since I bought my 2002 Tahoe with decent MPG results unless I am just doing in town stop and go driving. I decided to switch to 91 octane, premium, for this winter. I am completely surprised that I am doing way better on my MPG since I switched. I live where I work so unless I do get out on the interstate I do 95% driving in town. My rig just likes premium fuel way better, from Chevron.

91 isn’t going to give you better mpg. Didn’t see where you live but winter driving usually gives you better mpg (engine runs cooler, people including you driving slower etc....

For over a decade, all of our cars run better and get higher MPGs on Chevron brand fuel. Even our little Kia benefits from burning 93 over 87 but not much in that car. Makes a bigger difference in my truck and our GM minivans, 2+ MPG.

Once, my wife balked at the cost of fuel back in 2009 and put regular in our Montana as we were set to head out of state. A couple hours in I noticed our fuel burn seemed higher than normal and she fessed up. So instead of refueling north of Savannah, Georgia as was normal for this rig, we had to refuel in Brunswick. It often costs more money to burn the cheap stuff but it comes down to how much does it cost per mile to operate your vehicle on this fuel or that.

Now having said that, these new Generation V, direct injection motors nullify all that as my friend Gary @Miami-Dade has proven with his 2016 Tahoe. He still runs top-tier but says it makes no difference between 87 or 93, and to stay clear of Shell!

 

[iamdub]

91 isn’t going to give you better mpg. Didn’t see where you live but winter driving usually gives you better mpg (engine runs cooler, people including you driving slower etc....

higher the octane faster burn and so on.

I disagree. I, as well, get better MPG and can even feel a difference in power with higher octane fuel.

Fuel with a higher octane rating is more resistant to ignition, thus reducing its "flammability" and, ultimately its energy output. Fuel with lower octane rating burns more quickly so it has a higher energy output.

LS engines like higher octane and put out more power with it. I'm no tuner, but I'd venture to say its mainly due to the stock timing tables but also the compression ratio. The compression ratio of the 5.3 is 9.5:1 to nearly 10:1 depending on the generation. This isn't terribly high, but still higher than the previous generation of SBC of ~9:1. I have found that, on lower octane (which should yield more power), the LS engine gets a little preignition ("detonation", "spark knock", etc.) so the PCM retards the timing, which more than negates the potential power that the more volatile 87 octane fuel should produce. Running 89 or higher lets it keep the timing more advanced so it makes more power, which is increased efficiency. More efficiency = better MPG. During hot weather (90%+ of the year here), I can hear the spark knock and feel the reduction in power if I get ******* the throttle with 87 octane in the tank.

The cooler weather, especially in northern areas where they change the fuel blend, is kind of contradictory. Cooler air is more dense so the engine is inhaling more air volume per a given time span. The extra air volume increases engine efficiency and, therefore, its power output. This alone should increase its fuel economy since it has to work less hard to move the vehicle. But, the PCM has to add extra fuel to complement the extra air volume so that reduces the MPG. Also, if the fuel is "weaker" during the winter (whatever this "winter blend" is you guys get), then that will hurt MPG.

 

[iamdub]

For over a decade, all of our cars run better and get higher MPGs on Chevron brand fuel. Even our little Kia benefits from burning 93 over 87 but not much in that car. Makes a bigger difference in my truck and our GM minivans, 2+ MPG.

Once, my wife balked at the cost of fuel back in 2009 and put regular in our Montana as we were set to head out of state. A couple hours in I noticed our fuel burn seemed higher than normal and she fessed up. So instead of refueling north of Savannah, Georgia as was normal for this rig, we had to refuel in Brunswick. It often costs more money to burn the cheap stuff but it comes down to how much does it cost per mile to operate your vehicle on this fuel or that.

Now having said that, these new Generation V, direct injection motors nullify all that as my friend Gary @Miami-Dade has proven with his 2016 Tahoe. He still runs top-tier but says it makes no difference between 87 or 93, and to stay clear of Shell!

Cosigned.

My experience with various brands of fuels have shown Shell to be the worst. My Tahoe likes Chevron and seems to be fine with Exxon as well. FWIW: Stock tune, southern climate, heavy foot.

 

[mikeyss]

I run E85 all year around, I do a lot of city driving so my mileage is about the same on either E85 or 91. I lose a bit of power using 91 in my L9H though.

 

[swathdiver]

I run E85 all year around, I do a lot of city driving so my mileage is about the same on either E85 or 91. I lose a bit of power using 91 in my L9H though.

Lucky dog! The filling stations are quite proud of their E85 around here and for most of the year it's more expensive to burn than gasolina.

 

[hardluck13]

I run E85 all year around, I do a lot of city driving so my mileage is about the same on either E85 or 91. I lose a bit of power using 91 in my L9H though.

E85 has a higher octane rating.

 

[hardluck13]

I get it. Of course you’re gonna see some better throttle response with higher octane. Race cars don’t run 87.
But you can read 25 articles saying lower octane will give better MPG. Then turn around and read 25 articles saying the opposite. I wish I didn’t chime in. I was a little drunk not as drunk as I was much later after getting off the forum.

Sorry, not trying to be a forum know it all. I usually never say anything. Been on this forum almost 10 years and first time I’ve ever really said anything.

 

[OR VietVet]

91 isn’t going to give you better mpg. Didn’t see where you live but winter driving usually gives you better mpg (engine runs cooler, people including you driving slower etc....

higher the octane faster burn and so on.

Actually, the higher octane burns slower and that is why people say if you are getting a "ping" noise when accel to go to a higher octane fuel because it burns slower. I do mostly in town driving and I watched my mpg with the higher octane and it is better. Not like night and day difference but close to 1 mpg more for the same fuel used. I have not had it on the highway since I switched so I can't speak of what I may see with that, yet.


As a member of the forum you should chime in when you want about whatever you want. I ran shops for 35+ years and have been away from the shop atmosphere for close to 10 years now. I jump all over here at the forum because I have yet to work on or see some of what the newer designs are and I want to know. I ask questions all the time. Even at 67 years old, Christmas Eve, I still want to know and this forum helps so much.