Gas Mileage

[JCedar]

Hey guys, this is starting to bug me too much, I had to say something!

 

I have a 1999 NBS GMC Sierra, Ext. cab, Short Box, Z71 with the 5.3 120,000 miles on the truck. I used to get about 18MPG TOPS even with complete hwy driving. I do tend to give it a little gas ONCE and a while but I don't drive with my foot to the floor, I usually keep it below 2500rpms when accelerating to my hwy speed of 64mph. NOW I am getting 14-15, 16 if I BABY it . The last calculations have been with most hwy driving with a little city driving but NOT much.

 

I'm just wondering what it could be?? O2 Sensors?? Engine wear?? EGR valve?? I put new plugs, wires, fuel filter, PCV valve, and a K&N air filter 5,000 ago, and it never changed my mileage. My Cats rattle when my truck gets right above idle so I know those are going but I haven't gotten a code yet so I have let them go for now.

 

Am I just being a complainer here and should I take what I have or is there something wrong here? I wasn't going to bring anything up but I noticed everyone else talking about how they get 19-21MPG almost all the time on the hwy WITH the A/C on and running it at 75 mph and that just makes frustrated haha.

 

Thanks for your time,

John

[Wingnut]

My 02 gets 13.9 mpg...The only way I've ever gotten better, is to go 65 on the highway for a looooong time. I got well over 20 mpg when I did that.

 

I'd be pretty happy with your numbers.

 

Just a thought...Have you recently changed tire sizes? Because if you did, and didn't reprogram the computer, you odometer would be wrong, throwing off your mileage calculations.

 

Cats can cause a loss in mileage as well.

 

Especially when the fur clogs the intake filter.

[JCedar]

Wow, I'll have to give that a try and see what I get. I haven't made any tire changes, I have 265/75/16 BFG A/Ts, I think all Z71's came with 265s correct?? That's what it had on it when I bought the truck a year and half ago.

[JCedar]

Thanks for your input Wingnut.

[intruder217]

I almost always see a drop in mileage as cold weather approaches. Factor in winter blend gasoline and you can understand why your mileage drops.

[jonny_4.8_Z71]

I have the same problem, I used to get around 16-18 in september, now I can't get any better than 14.5 on a 4.8l. Of course I did crank the t-bars and put on new tires.

[Bruce03Silverado]

I am getting 15-16mpg out of my 03 4.8l, 4x4 ECSB. I do have a Volant and 285/75/16 BFG's though. I could probably do better if I drove more highway, but most of it is stop and go a few miles from the house.

[mcreyaufmiller]

I second the motion on the winter blend gas. I have been averaging 12 MPG, so you are lucky. But I drive with my foot in the injectors, and the tires spinning!

[budhayes3]

I second the motion on the winter blend gas.  I have been averaging 12 MPG, so you are lucky.  But I drive with my foot in the injectors, and the tires spinning!

 

<{POST_SNAPBACK}>

 

 

Yea, and a third here, we see it alot at the dealership this time of year, alot of concerns in relation to poor fuel economy.

[JCedar]

I have heard of bad gas mileage during winter months, but I didn't think it had such an effect. I must say though you guys are the S**T. haha Everyone is just awesome on here, I Love it!!!

[Wingnut]

That's why some of us stick around for....Oh...3000 posts or so.

 

A bit more, if you count the other userid that I was originally using.

[ManyCamaroz]

The two things men lie about most:

 

1) Gas Mileage

 

2) Women

 

[JCedar]

The two things men lie about most:

 

1) Gas Mileage

 

2) Women

 

 

<{POST_SNAPBACK}>

 

 

 

haha, yeah I'm with you on that one! I'm not gonna call anyone a liar but I know someone that recently told me he got 22 MPG out of a 97 5.7 ext. cab short box Z71. Hmmmm that MIGHT be a little over the top buddy!

[Wingnut]

Depending on the circumstances, I wouldn't doubt it.

 

I've hit 22 mpg in my 02 (going 65 on level ground for a couple hundred miles). And I hit 24 in my old 89 (long bed, reg cab 5.0 liter) going 65 on a several cross-country trips. With a 34 gallon tank...I had to stop and use the restroom twice between fill-ups, which were over 700 miles apart.

 

BTW, I wouldn't lie about gas mileage...There would be no point. I normally get 13.9 (very consistant) in my 02...But it is cabable of getting better than 20.

 

But if he's claiming that he gets that kind of mileage consistantly, and in town...Yeah, I would say he's snowing you a little.

[catmandoo]

I have noticed that I go from 600km(375 miles) per tank in the summer to around 500 (310 miles) in the winter.

 

PS. I have a 98 Z71 ext cab with 5.7 vortec and 245 tires.