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Fuel Grade And Increased Mileage


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Hi all,

 

I have a 2008 2500HD with the 6.0 litre and with about 18,000 km on it. I have always run regular gas and get what I consider average mileage at about 11 MPG. I do city and highway and tow a 28' fifth wheel most weekends during the summer. It has an Airaid intake and Jet TBS, everything else is stock, so far.

 

I am wondering if any one has gone from using regular gas to mid-grade or premium gas and noticed any real difference with their MPG? Would it make any difference if I changed the spark plug wires to a thicker set??

 

Any thoughts???

 

Thanks.

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  • 2 weeks later...
I don't think you'll see any difference. About the only thing I could suggest is getting a tune and see if that helps.

I see a big difference in grades of fuel and always buy premium when I'm going on the road. The overall average seems about the same no matter what fuel is burned but on highway trips, I can only get over 20 mpg, if I buy premium and it has to be brandname like Amoco/BP, Shell or Mobil. Cut rate gas will run the same as regular even if you buy their premium. I don't believe in buying cheap gas.

 

I tried buying regular for awhile when it first went over $3 a gallon and found that I was unable to get over 16 mpg in my 99 Tahoe on roadtrips. This truck always got anywhere from 21 to as much as 25 mpg on the road when I burned premium. Wind conditions are a big factor and side winds or headwinds will cause the variation by as much as 4 or 5 mpg. When I got 25 mpg, probably had a nice tailwind for most of the trip.

 

People think I'm nuts when I talk about this but I have tested it so many times that I believe it. I have checked mileage on nearly every full tank of gas that I've put in both our 99 Yukon and our 99 Tahoe. We have a cabin that is 350 miles from our home and both trucks have made this trip many times with the results that I mentioned. The Yukon rarely gets above 20 mpg and is more likely to be around 19 mpg even on the road with premium gas. I've never understood why the Tahoe was able to do so much better. They are virtually identical vehicles, same motor, same drivetrain, 5.7 with 3.73 limited slip and push button 4wh with auto option. The overall average for either of them is around 13 mpg, no matter what gas is used. As I said, I don't bother with premium unless going on the road as it doesn't seem to matter for everday driving, still won't buy cheap gas. Lots of water in the offbrands and many are selling very old gas.

 

Bill

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If your vehicle is designed to run on 87 then put 87 in it. Putting a higher octane in it you will lose hp because the higher the octane the slower the burn in the combustion chamber. Gas mileage would suffer too and given the fact you spent more for it per gallon only makes the outcome worse.

 

If you have a tune or a programmer installed and you have it set-up for higher octane then you must run higher octane or you will get detonation.

 

I'm sorry but I can't believe one can get better mileage by running high octane on an 87 octane rated motor... :)

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If your vehicle is designed to run on 87 then put 87 in it. Putting a higher octane in it you will lose hp because the higher the octane the slower the burn in the combustion chamber. Gas mileage would suffer too and given the fact you spent more for it per gallon only makes the outcome worse.

 

If you have a tune or a programmer installed and you have it set-up for higher octane then you must run higher octane or you will get detonation.

 

I'm sorry but I can't believe one can get better mileage by running high octane on an 87 octane rated motor... :)

So, what are my trucks rated for? I don't even know but I think they say to burn regular. Might actually call for 89 octane, not sure. I did this same thing with an old vette with 5.7 as well as a z/28 and could get 25 mpg highway with both of them burning premium. Those two, I never actually compared with regular, always burned premium. I'm only guessing the the premium helped both of those vehicles because of my other experiences.

 

I also proved this same thing to myself many years ago with a Ford bronco that I bought new in 79. I never met another owner who got 18 mpg on the highway except one guy who had one with a 302 and had overdrive, he got as high as 20. Mine was a 351M, four speed with granny and low gear open rear end, I don't know what the ratio was but low. If I went over 65, I would lose mileage. I attribute part of mine to having a stick but was never sure. Premium made a difference and any Ford I ever had seemed to do better, even run better on premium. Sorry to mention the F word here. :)

 

Bill

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  • 5 weeks later...
If your vehicle is designed to run on 87 then put 87 in it. Putting a higher octane in it you will lose hp because the higher the octane the slower the burn in the combustion chamber. Gas mileage would suffer too and given the fact you spent more for it per gallon only makes the outcome worse.

 

If you have a tune or a programmer installed and you have it set-up for higher octane then you must run higher octane or you will get detonation.

 

I'm sorry but I can't believe one can get better mileage by running high octane on an 87 octane rated motor... :jester:

So, what are my trucks rated for? I don't even know but I think they say to burn regular. Might actually call for 89 octane, not sure. I did this same thing with an old vette with 5.7 as well as a z/28 and could get 25 mpg highway with both of them burning premium. Those two, I never actually compared with regular, always burned premium. I'm only guessing the the premium helped both of those vehicles because of my other experiences.

 

I also proved this same thing to myself many years ago with a Ford bronco that I bought new in 79. I never met another owner who got 18 mpg on the highway except one guy who had one with a 302 and had overdrive, he got as high as 20. Mine was a 351M, four speed with granny and low gear open rear end, I don't know what the ratio was but low. If I went over 65, I would lose mileage. I attribute part of mine to having a stick but was never sure. Premium made a difference and any Ford I ever had seemed to do better, even run better on premium. Sorry to mention the F word here. :P

 

Bill

 

 

I know when I bought my 08 GMC 1500 Sierra ext cab 4x4, they told me never to run premium, as the ecm is designed for 87 octane, and I wouldn't be doing myself any favors. I know this is comparing apples and oranges, or more like stone age to atomic age, but in the past with other vehicles I have had the same experience as Bill. My previous truck was a Dodge Ram 1500 360, and it seemed no matter how I drove that thing my mileage was 10mpg...end of story. A mopar friend of mine recommended I run 92 octane, and I would see a huge increase in mpg. Well, I wouldn't go that far, but it DEFINITELY made a difference. However, with different times, different technologies, I can see why one would not mess with changing octanes on these engines, unless throwing a tune into the mix.

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If an engine can be efficient on 87 it will be no moreso on higher grades. There is a caveat to that statement however. Higher grades of fuel in general have better additive packages than that of regular gasoline. This stuff is all blended in at the truck load outs off of the refineries. I know, I am Instrument Technician by trade and when we are slow I do small maintenance projects for Shell and Petro Canada's truck load outs.

 

You will see things blended like ethanol, tactrol, nitrogen and whatever else the specific end user ( gas stations) dictate. We only have two base stocks that deal with automotive applications being regular and premium. Ethanol is used to raise the pump octane number beyond 91 now. That may be an attributing factor as well. Ethanols lower BTU content could cause mileage changes. The max blended here is about 10% so a 2-3% drop in economy may be percieved....... hardly enough to notice.

 

So why do you see mileage changes? Timing and detonation mostly.

 

My 97 Monte Carlo got more consistent mileage on 89 midgrade than on 87 octane gas. Why? The 9.6:1 compression 3100 was rated for 87 fuel. I also bought the car used with about 75000 miles on it. Carbon can cause hot spots and give pre-ignition that higher octane fuels can counter. That and I think the timing was able to advance as much as possible under cruise conditons whereas again, it couldn't on 87. The change to 91 or higher gas made no difference whatsoever.

 

There is nothing really odd or secretive about fuels. They combine the Research and Motor octane numbers and divide by two to get your pump octane value. Not all 91's or 87's have to equal either. It is more desireable to have Motor octane value as close to the research number as possible. This shows the fuel does better under higher load stress. That is not always the case though and you could lose power to detonation in that case even though you shouldn't be.

 

So really a higher grade basestock with a better blend package may show some inherent benefits to an engine that shouldn't technically require it. Testing however is the best method. My 09 2500 HD's LY6 as an example runs absolutely no better on mid grade or premium than it does on regular gas.

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  • 2 weeks later...

Hi all,

 

Thank you for the responses. I tried going with the 87 octane and the only difference was a lighter wallet. Will stick with regular gas and will think about getting a tune or easing off on the gas pedal......Mind you I need to have the larger aftermarket gas tank before I do anything so I can drive to the places that I want and need to go with the 5th wheel and family.

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I know when I bought my 08 GMC 1500 Sierra ext cab 4x4, they told me never to run premium, as the ecm is designed for 87 octane, and I wouldn't be doing myself any favors. I know this is comparing apples and oranges, or more like stone age to atomic age, but in the past with other vehicles I have had the same experience as Bill. My previous truck was a Dodge Ram 1500 360, and it seemed no matter how I drove that thing my mileage was 10mpg...end of story. A mopar friend of mine recommended I run 92 octane, and I would see a huge increase in mpg. Well, I wouldn't go that far, but it DEFINITELY made a difference. However, with different times, different technologies, I can see why one would not mess with changing octanes on these engines, unless throwing a tune into the mix.

 

 

Another BS dealer story, read your owners manual.

 

its a myth, you gain nothing but an empty wallet by running higher octane then your tuned for...if you get it tuned for more octane you will see results

every vehicle reacts different. Before i put my leveling kit and taller tires i always averaged 16.5. Decided to try shell 93 and after the first tank i was at 17.8 and from then on stayed in the low 18's and its stock with no mods. everyones results are different, just because you didnt see any benifits doesnt mean everyone else will.

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I havn't been very attentive to the octane level of the fuel I use, I use "regular", and that's it. I have used medium and my truck didn't run any better, and didn't help the mileage any. I used premium and it seemed to lose power and mileage sucked. So I use the regular and keep it there. I have considered using E85, but I'm not sure if that's a good idea or not.

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Using high-octane gas in a car designed for regular accomplishes little except more rapid combustion of your money. Some refuse to believe this, claiming, for example, that premium gives the family Toyota better mileage or more power. These people are in dreamland. Others say premium is purer or contains detergents that will cleanse your engine of uncouth deposits. Likewise misguided thinking--government regulations require detergents in all grades of gasoline. Believe what you like; the point is, don't assume "premium" means "better.

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OK - so lets say you are tuned for premium.....

 

actually lets say you AND a buddy are tuned for premium and that both of you keep records of mpg's pre-tune and post-tune....and both of you show (both pre and post tune) better mileage with 89 than 93. mpg differences range sometimes over 1mpg.

 

what 'splains that?

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Using high-octane gas in a car designed for regular accomplishes little except more rapid combustion of your money. Some refuse to believe this, claiming, for example, that premium gives the family Toyota better mileage or more power. These people are in dreamland. Others say premium is purer or contains detergents that will cleanse your engine of uncouth deposits. Likewise misguided thinking--government regulations require detergents in all grades of gasoline. Believe what you like; the point is, don't assume "premium" means "better.

 

If I want premium for the octane level, I'll go hit up the airport and buy a few gallons. What effect would 100 octane have on a 5.3 liter engine?

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