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Old 09-24-2013, 11:19 AM   #1
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GMC Sierra?

Hey. New here. Found this site though google. I am hoping someone can tell me how I can get more MPGs out of my 2008 4 door gmc sierra z71 with the 5.3. i'm getting 15/19 right now. It drops to v4 mode on highway but that only works on long trips.

Any ideas? I put a Magnaflow exhaust on it, but it made very little difference.
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Old 09-24-2013, 03:37 PM   #2
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Exhaust upgrades like yours are among many popular investments that, unfortunately, never pay back in fuel economy savings. You have probably seen plenty of other ideas for things to spend your money on that promise increased fuel economy, but they won't deliver either.

The quick, easy thing you can do is increase your tire pressure. Don't exceed the maximum marked on the tire, but do exceed the minimum recommended by GM. It's not huge but it's free and will also increase tire life and durability.

After that your options are driving style adjustments/techniques and more radical DIY modifications (mostly aerodynamic stuff, and potentially ugly).

Do avoid using the brake pedal (whose purpose is to discard energy; that's energy that you spend fuel to make and will spend more fuel to re-make) and try to keep RPM low. If there's a red light far ahead, brake a little bit immediately so you can cruise through a green light at a moderate speed instead of holding your current speed and completely stopping at a red light. Keep a long following distance so you don't have to do every wasteful thing the driver in front does. Plan ahead to ease up to curves and roll through them instead of staying on the go-pedal and then braking for the curve.

Of course reducing speed will help, but you didn't need to come here to learn that, so we'll assume you already drive as slow as you are willing. I don't think it's worth holding up traffic (though I do think obeying the law is, since tickets and the resulting insurance rates are so expensive).

One thing that is counterintuitive is that you shouldn't necessarily accelerate too gently. You want to get into higher gears in a shorter distance, and too-gentle acceleration with an automatic means it will go further in low gear.

The very best thing you can do, which supports ALL of this and anything else you might try, is to faithfully log your fuel economy. You can take advice all you want but until you have numbers and graphs showing trends over multiple tanks as you experiment, you can never know what works for you and what doesn't. Start a gaslog here or at Fuelly.com and put every tank in it along with notes about what you did.
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Old 09-24-2013, 04:35 PM   #3
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+1 to everything HC said... I have a 98 GMC K1500 Z71, and I feel your pain. The whole reason I bought my Escape Hybrid was I was tired of buying $80 worth of gas every week. Here's a couple things to consider...

Chevy V8's respond well to driving under load. Pretty much, you don't use the cruise control. You pick a throttle position that holds you close to the speed limit on flat ground, and won't gain or lose much when you hit hills.

Get a ScanGaugeII. You can program it with stuff like instant fuel economy readings and such to help you learn right away what works, and what doesn't on your vehicle.
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Old 09-24-2013, 06:22 PM   #4
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I currently own a full size gas truck too(1994 F-150), and even though it gets pretty good mileage (21 mpg at last check), the best thing to do to improve your fuel economy is to drive different. It will give you the absolute greatest gains. A Scan Gauge 2 will also be a GREAT investment and would be the only purchase I would make to improve your mileage.

Those fuel economy "chips" you can buy are all snake oil. Stay away from them. Even the computer programmers, with the exception of maybe EFI Live, I would stay away from. If you were to get a tune done with EFI Live, you may be able to make the truck run more often on 4 cylinders for better fuel economy.
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Old 09-29-2013, 07:44 PM   #5
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I had Silverado with 5.3 Vortec. NOTHING works. Day or night, traffic or or not, winter or summer, it's 15.7 average.
Rid of it. Unfortunately, to get to promised great truck mpg land, you must pretty much drive non stop FWY.
And there is no better mpg choices in truck realm. None. Tundra is as bad if not worse.
I now ride 09 Ridgeline. I do not regret ridding of my Silverado at all.

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Old 09-30-2013, 05:03 PM   #6
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I've done a little better with the 5.3 GM full size when I was driving it regularly.
Bessy :
Lifetime Fuel Economy: 17.09 MPG(US)

Gaslog data for Bessy

Only modification was increased tire pressure. 40% highway, 60% country/town roads. Also quite a few low-mile hours doing yard truck duty.
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Old 09-30-2013, 07:16 PM   #7
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I can pull 18 out of my 98 Sierra when its fully loaded, a/c on, and cruise set on 70. EPA highway rated for 16.
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Old 10-01-2013, 03:24 PM   #8
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I have hit 21 in my '98 Sierra (350 V8, 3:42, 2WD) at about 60-65 mph with some drafting. It doesn't seem to matter much whether the A/C is on - about 1 mpg is all the difference.
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