Bad MPG ?

Teal03 · April 9, 2004

I have a 2WD 2003 silverado with 5.3, auto, 3.73 gears, G80, Z82, Z85, & stock P255/70R16's tires. The window sticker says I should get 16 city & 19 hiway. The truck has 6400 miles on it now. I drive 30 miles per day and 26 of those are at 70MPH (flat ground). The truck rarely sees over 3000RPM. My only mods are a K&N drop-in filter, soft bed cover, and I use Mobil 1 5W-30. I use 90 octane 10% ethonal blend gas. I get 14.5MPG . Do I hold out in hopes that it gets better with age, or do I go to the dealer to check out the brain? Or is it the gas I use? I'm not looking to spend $$ on mods to bring this up just wondering if this is par for the corse? Thanks for your input.

Rich G.

Wingnut · April 9, 2004

My 02 only gets about 13.5 mpg on average.

It doesn't get better mileage, nor does it run better on higher octane fuels.

Funny thing is, my 92 has the TBI 350 in it, and I have gotten as high as 17 in it. 15 average.

lrymal · April 9, 2004

I have a 2WD 2003 silverado with 5.3, auto, 3.73 gears, G80, Z82, Z85, & stock P255/70R16's tires. ...

Sure would be nice if youse guyz with problems would update your profiles and let folks know where you are. My reaction to the MPG issue vs. the sticker is that you have winter-blend gasoline and are up north somewhere. Because of that, your gas mileage is low. As they bring in warm weather blending, the mileage will improve--considerably.

Anyway, that's just a guess on my part.

Shaners · April 10, 2004

Don't worry, it'll get better. It takes awhile to break these engines in.

Ethonal is bad... everyone that runs it complains of bad MPG's... The same goes for Oxygenated fuel.

Run 87 Octane in your truck, and run good fuel... As the summer approaches your milage should increase as long as the A/C isn't running full blast.

Good Luck and have faith!!!

redvett · April 10, 2004

In cold weather the PCM will add fuel to get the correct A/F rario and in the summer will subtract so winter blend is only one portion of the pie so to speak. If you start your vehicle and let it warm up or idle for more than a minute or so you are killing you mileage. GM engines need at least 9-10000 miles to be broken in. I have bought and owned 2 new GM vehicles every other year for 40 years and keep very good records and the records show fuel & oil mileage improving after 10-12000 miles.

Teal03 · April 10, 2004

Well thanks guys for your input I will switch to 87 and wait out the mileage on the truck. If any one else has some thing to say I'm all ears. Thanks again.

Rich G

iron_786 · April 10, 2004

when i had my 92 with a 305 2wd i was lucky to hit 14 mpg, i tried the high octane was no better or no worse so i saved my money and used 87 octane...

now with my 2002 283, 4wd im doint about 13-14 avg, i guess i cant complain i got way more power and 4wd but i would like a tank to go further too.... and i do miss the 34 gallon tank on my old truck,,,,, seems im fillin up all the time now.

so i think ur truck is running as expected, the window sticker was just to make a sale u will never see 19 mpg. unless u buy a little ricer 4 cylinder

GM5.3V8 · April 10, 2004

Wow that is low. FYI I'm in southern CA, using 87 octane. Truck is 2003 1500 LT (which comes with the 5.3, 3.70, locking diff), ecsb. Mods are: Bruteforce intake, Spin-tech cat back, Line-X, Undercover hard tonneau. I drive A LOT, already have 22000 miles, commute 100 miles/day roundtrip, I'd say my overall driving mix is 70 highway/30 city streets. I've consistently averaged 17.5 mpg, smack in the middle of 16-19 rated mpg. Hope your truck mileage will improve.

airbalancer · April 10, 2004

the ratings are done at a speed ofabout 50mph inside, so there is no headwind, temp is same. it is just used to compare one truck to another under contoled conditions.That is why you will find tires that have the lowest rooling resistance on base models to increase mpg.

I could get my son to write a paper on this but since he is engineer it would be long and boring.If you want good mpg get an echo.

Teal03 · April 10, 2004

Thanks guys kieep the ideas coming. I use 90 octane with ethonal becouse here in Iowa and the mid-west in general it is less per gallon($1.75 rather than $1.78). The states around here subsadize(sp) it becouse of the corn it comes from.

Rich G.

az'03Silverado · April 11, 2004

Teal03

I have a 2003 Ext cab with the 4.8L and 10500 miles. All of my driving is in the city and I rarely go on the freeway. I've been averaging 15-16 mpg. I run 87 octane. One thing I've tried which helped a little was pumping the tires up slightly. Instead of 35-36psi, I went up to 40. The sidewall says max is 44 so I figured it is safe enough to do so. It rides a little firmer and the bumps are a little more pronounced but I've added a little less than 1mpg. Also, being in AZ during the summer the higher pressure keeps the tires cooler due to the decreased resistance and flex.

03GMCSierra4.8L · April 11, 2004

2003 4.8L 3.42's RCLB Sierra, 11,500 miles, Soft Bed Cover, No additional mods. Get 16 city, 20-22 on the Interstate at 70mph. Towing our Pop Up (1500lbs) consistantly get 18-19 on the highway. Got these numbers since day one with 2 miles on it at delivery. Live in Northern Indiana and had a B@!#$ of a winter this year. Only have used 87 oct. fuel, have found in the past that higher Oct does nothing for mileage in fact has hurt preformance in a past gm vech.

jnash67 · April 11, 2004

Hello,

Just reading about the mileage woes with the new Silverado's. Contrary to most, there is more power in 87 octane gas then 91+ offerings. You can find alot about it on the net, sorry for not posting a url for the info. I own a 96 Impala SS, and that was the first thing all of us owners did, fill up with the premium. Well, not only will your mileage be down, you can cause a carbon build up in the combustion chambers over time. For what its worth, my 2000 gmc Yukon XL 4wd, with 5.3, 3.73, and a drop in K&N gets 13.5 +/-, and about 17.5 on the road in the summer. It also has 99k on it.

Markeaux · April 12, 2004

This is an interesting read on gas and octane, etc:

http://www.vettenet.org/octane.html

HillHound · April 12, 2004

My '01 Z71 ext cab with 5.3L and 4.10 differential averaged 13/14 mpg and would even get down to almost 12 if I ran it hard. On highway trips the most I ever saw was a little over 16 mpg.

I think alot of guys on the internet flat out lie about their mileage and the original poster's truck sounds like it's right where it should be, maybe a hair low for a 2wd but considering the time of year and low mileage nothing to worry about.