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How To Improve 6.0 Gas Mileage?


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#1 ToddH

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Posted 23 February 2008 - 08:51 AM

Alright guys help me out here. I have an 04 GMC Sierra 2500HD, Ext cab, 4wd,285 tires, 6.0/4.10 and I am getting 10-12 mpg. I know they don't get good but I was hoping for 14. I am not what I would consider a lead foot, so what can I do? I don't want to spend a ton of money, before I do that I will just trade it in on a new 5.3. Thanks in advance.

#2 CM7

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Posted 23 February 2008 - 11:00 AM

i'd start with some normal maintenance, fuel/air / oil filter, check plugs. check for proper air pressure in tires.

then u can get a diablo predator hand held tuner for about 3 bills that can help out about 1-3 mpg depending if u run 93 or 87 octane plus get some more power out of her. plus a cold air performance intake may help.

but if u dont need a truck that big maybe getting a 5.3 willbe your best choice. those 4.10's and 285's arent helping your quest at all... 14 mpg might be a lil out of sight.
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#3 ATMINF

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Posted 23 February 2008 - 11:03 AM

I can tell you city driving it will only be in the 12-13 max and on the hwy they range from 14-17. The only thing I have heard works to get about a extra mile in the city and mile or two on the hwy is with a economy tune from on of the PCM tuners. Call them up and see what they can do for you. I have a mild performance tune and I get 12-13city and 16-17 hwy, my tune is from Charlie Wheatly. Good luck, also the 6.0L gasser are known to drink gas, not as bad as a big block but close.

Edited by ATMINF, 23 February 2008 - 11:04 AM.

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#4 pm26

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Posted 23 February 2008 - 11:10 AM

Try premium (93 octane) brand name gas like Sunoco. You may pickup about 2 MPG. The cost of the fuel is slightly higher, but you may see some benefits.

#5 steveyrock

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Posted 23 February 2008 - 12:57 PM

drive the truck less and by a four cylinder car for most of your driving.. When regular gas goes up another dollar a gallon the 5.3 motor will not make you happy. Consider a Colorado with a smaller engine. Bottom line is if you want to drive a big powerfull truck you have to pay the price.

Tunes and cold air intakes won't help the MPG's very much but driving the truck less will keep you away from the pump more than any mod.
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#6 gave20

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Posted 23 February 2008 - 01:42 PM

Alright guys help me out here. I have an 04 GMC Sierra 2500HD, Ext cab, 4wd,285 tires, 6.0/4.10 and I am getting 10-12 mpg. I know they don't get good but I was hoping for 14. I am not what I would consider a lead foot, so what can I do? I don't want to spend a ton of money, before I do that I will just trade it in on a new 5.3. Thanks in advance.


Get rid of the 285's and switch to 245's, and I bet you pick up the 2mpg. I switched from 245's to 265's and dropped 2-3 mpg. If you don't like that option get a tune, should pick up a few miles overall.

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#7 sonjaab

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Posted 23 February 2008 - 02:14 PM

The reason for lower mpgs when switching from 245s to 285s is your
odo/speedo is off !
A tuner/PCM burn or a PCM reflash at the GM dealer is in order............

My 04 x-cab 4x4 4:10s 2500 got 10 city and 16 hiway bone stock unloaded ac on!
My 07 x-cab 4x4 3:73s 2500 GMT-900 gets 13.5 city-17 hiway also bone stock.......
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#8 DarrenWS6

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Posted 23 February 2008 - 02:19 PM

only way is to get another daily driver. Im ditching mine for a 1500 becuase I dont need this much truck anyways. thinner width tires & a PCM tune should help a little bit more though
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#9 omegafiler

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Posted 23 February 2008 - 02:24 PM

Yeah, all of that will help. Econo tune, free flow exhaust, narrow tires, drive like grandma, etc. IF you can drive it easy enough, you just might see an increase. Otherwise, it is a 6.0.

But then again, you also need to keep in mind that with gas prices constantly increasing, your "gains" may not last all that long. So if you drive enough, a 2nd econo car might be a good idea. Or if you're going to trade it, better do it ASAP. As gas prices increase, the value of gas guzzlers isn't going to get any better.

#10 Stratosman

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Posted 23 February 2008 - 07:48 PM

The reason for lower mpgs when switching from 245s to 285s is your
odo/speedo is off !


Not necessarily. While you are traveling farther than the odo reads of not corrected for bigger tires, you also have to use more gas to get them to turn. Here's what I saw in my truck:

245's:
400 miles/34 gal tank in town (actually using about 32 gal)
425 highway

285's:
370 miles in town
420 highway

As you can see my highway mileage is basically the same, but in town I lost about 1 mpg. Worth it I think.
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#11 sonjaab

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Posted 24 February 2008 - 12:17 AM

Sorry Billy.....You guesstimate is OFF!

Larger tires make your odo/speedo read slower and less miles traveled.
(with larger than stock tires and no PCM reflash)

Edited by sonjaab, 24 February 2008 - 12:20 AM.

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#12 HD Sierra

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Posted 24 February 2008 - 03:39 PM

I have about the same truck that you have, exxcept mine is a little newer and I have 265x17 tires on Hummer wheels...

Mileage is about the same as yours. Even with the original tires and wheels, I never got 14 even on the hiway....about 13.8 is a close as I could come....ugh

SO I change the tires and both power and mileage went south. I tried an AEM Brute Force CAI....looks very pretty but nothing changed.

Then I put on a flowmaster 50 series big block cat back...sounds fantastic, but that was all that changed....just more noise that my wife hates...

Next I put in Pennzoil Platinum syntheric oil....supposed to increase mpg....no change at all. Well, maybe in 100,000 miles I will save a gallon or two...ha

Then I went to the Diablo Predator...I used the tune for 87 octane and reset the speedometer to match the wheels and tires. Now the speedometer is accurate, the shifts are nice and firm, I think I might have gained back some of the lost power from the tire change, but the mpg is still the same. I drive like an old lady and seldom go over 65....ugh.

Several folks have suggested that I go to the 91 octane tune on the Predator, but premium gas is $.30 a gallon higher here, so unless I get 5+ more mpg, it is still a lost cause, and 5+ mpg increase is a rediculous quest anyway.

Others have said to get a custom tune for another few hundred bucks....I talked to a couple of the custom tuners, and I am not convinced that can do any better in terms of mpg....

It is what is it, my friend....a 6.0L gas engine in a 3/4 ton truck that weighs about 6800 pounds and has 4.10 gears.....never designed to be an economy king, but it pulls like crazy!!

We have a 5th wheel trailer, and it pulls it anywhere I want to take it. If I ever sett the RV, I'll spend a few hundred and have 3.55 gears put in for straight driving, and that will probably net me 1-3 mpg (my goal here is to keep the rpms down so I don't wear it out).

I really like the truck and even at $4.00 a gallon (and we are getting there), I'll keep the truck and drive it less and less. I have a 91 Town Car that gets and honest 24 mpg hiway, and it is my daily driver. When the town car goes, I'll look for something with a V6.

I dirive my truck one or two nice days a week, never in the snow or rain, and it just turned 7,000 miles.

One of the disadvantages of the HD series is that you cannot get the fuel management system where it switches to running on only four cylinders....I can understand why it is not standard, but I ould have bought it as an option, since I don't need all the power all the time.

Sorry this got so darn long...I like talikng about my truck...ha

Good luck.
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#13 Rudy35

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Posted 24 February 2008 - 06:50 PM

Good gas mileage really is about going easy and keeping your tires properly inflated. In December I drove a 550 mile round trip and got 15-15.5 mpg. But I set my cruise at about 68 mph and never went over 70. Most of our driving, back and forth to work, store, etc, is tough on mileage. In winter the mileage is worse (cold temps, 4X4 use). When warmer weather comes it will improve, just in time for the summer gas price increase!

My uncle once said that "If you want to ride a big horse, you have to buy a lot of hay"
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#14 demented

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Posted 24 February 2008 - 06:54 PM

I have about the same truck that you have, exxcept mine is a little newer and I have 265x17 tires on Hummer wheels...

Mileage is about the same as yours. Even with the original tires and wheels, I never got 14 even on the hiway....about 13.8 is a close as I could come....ugh

SO I change the tires and both power and mileage went south. I tried an AEM Brute Force CAI....looks very pretty but nothing changed.

Then I put on a flowmaster 50 series big block cat back...sounds fantastic, but that was all that changed....just more noise that my wife hates...

Next I put in Pennzoil Platinum syntheric oil....supposed to increase mpg....no change at all. Well, maybe in 100,000 miles I will save a gallon or two...ha

Then I went to the Diablo Predator...I used the tune for 87 octane and reset the speedometer to match the wheels and tires. Now the speedometer is accurate, the shifts are nice and firm, I think I might have gained back some of the lost power from the tire change, but the mpg is still the same. I drive like an old lady and seldom go over 65....ugh.

Several folks have suggested that I go to the 91 octane tune on the Predator, but premium gas is $.30 a gallon higher here, so unless I get 5+ more mpg, it is still a lost cause, and 5+ mpg increase is a rediculous quest anyway.

Others have said to get a custom tune for another few hundred bucks....I talked to a couple of the custom tuners, and I am not convinced that can do any better in terms of mpg....

It is what is it, my friend....a 6.0L gas engine in a 3/4 ton truck that weighs about 6800 pounds and has 4.10 gears.....never designed to be an economy king, but it pulls like crazy!!

We have a 5th wheel trailer, and it pulls it anywhere I want to take it. If I ever sett the RV, I'll spend a few hundred and have 3.55 gears put in for straight driving, and that will probably net me 1-3 mpg (my goal here is to keep the rpms down so I don't wear it out).

I really like the truck and even at $4.00 a gallon (and we are getting there), I'll keep the truck and drive it less and less. I have a 91 Town Car that gets and honest 24 mpg hiway, and it is my daily driver. When the town car goes, I'll look for something with a V6.

I dirive my truck one or two nice days a week, never in the snow or rain, and it just turned 7,000 miles.

One of the disadvantages of the HD series is that you cannot get the fuel management system where it switches to running on only four cylinders....I can understand why it is not standard, but I ould have bought it as an option, since I don't need all the power all the time.

Sorry this got so darn long...I like talikng about my truck...ha

Good luck.



That's the best explination of what everyone can expect from a 6.0 liter than I have seen yet. Nice job!!!!

I have done all the things that everyone has said or done and still only get about 12 to 14 mpg. It is what it is. That's the price I have to pay. Oh well. I do love the truck. Now if only we could get the price of gas back down to a reasonable level.
Careful with that thing,You can poke your eye out!!!

#15 ATMINF

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Posted 24 February 2008 - 08:23 PM

Are you guys using gas that has some ethanol in it? I remember when I was up in Wisconsin even the "regular" gas had about 10-15% Ethanol in it(except some the 87), and that could cause the milage to be a little lower than what I get down here in the South. But I can honestly say that on the Hwy doing 75+mph I still get over 16mpg. And on my 3/4ton 2001 Suburban I would get 17+mpg on the freeway. I don't know if I am just lucky or its because of the 2wd, sythetic oil, rear end fluid, and syn Trans fluid?? I just a bunch of small factors adding up. But like others have been saying a 6000 lbs truck is never going to get great mileage.
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