Mileage worse then when i bought the truck

[yz2009]

I have a 2004 GMC Sierra extended cab with 102k miles that i bought used in 2008.

 

When i bought the truck i recorded the mileage at fill ups and i would get about 18mpg if doing all highway driving. Around town i would usually get 13-14mpg.

 

Fast forward 3 years. I recently decided to see what my milage was on a trip. I drove 70% highway and 30% around town. I only got 13.5mpg. On the past 2 fill ups ive only gotten 11mpg then 10.5 mpg. This is much lower then when i bought it. The only thing that i have changed sense i bought it was changed the tires. It came with Bridgestone Dueler all terrain and i recently put Wild Country all terrain tires on it.

 

Is it possible that the new tires causes such a big drop in mileage. The truck runs great and still seems to work the same as the day i bought it.

[pm26]

You may want to consult the crowd on this site who claim to consistently get 20+ MPG out of similar trucks, and there is plenty of them.

[yz2009]

Dont get me wrong i know its a truck and is going to get bad mileage and i have no issues with the original mileage i got. Im just trying to figure out why the drop in milage.

 

BTW its a 5.3l

[jdubub]

It's def possible. Are they the same size as the bridge's? Even if they are, they could weigh more. Also, the fuel you have been getting could be pretty crappy. As the years go on the fuel has gotten a hair worse quality wise. ALSO, you may need a tune up if you haven't done one recently. Were there any strong winds on the last trips you tracked?

 

If the tires are the same size as original, I am willing to bet you just need a good tune up.

[KMGZ400]

maybe a simple tune up could help... filter plugs etc

[yz2009]

I recently had the dealership do a tranny flush and new fluids. Putting new plugs and wires in is on my list of things to do. I was reading about motor vac. Should i be considering talking to the dealer about it? Like i said its got 102k miles and off the top of my head i think around 2600 hours.

 

Fuel quality could be it but 9 times out of 10 i fill up with mobile. No abnormally strong winds or anything.

[ifshinxs]

How old are the Cats? Sometime they get plugged up and need to be replaced. Just something else to think about.

[thinkgreen216]

On my 07 I would average 19-22 on the highway (with a 70 MPH speed-limit) with the stock 265 Wranglers then when I went to a 295 Firestone Destinations MT my mileage dropped to 14-17 on that same highway, sucks but the MT's look so much better.

[TJay74]

I just purchased a 2001 with 130k miles. On the first run thru it got 13mpg. I changed the plugs, fuel fiter, air filter, and cleaned the MAF. Next tank it got almost 18.5mpg. Last week with more city than highway it got 15.5mpg.

[dewfpo]

There's not much you can do with the tires so I'd bet a good tune-up will probably help some.

 

DEWFPO

[hodo78]

I also dropped from 18mpg on the highway at 70mph down to 16.5mpg when i went from the stock wranglers to the 285/70/17 D series Toyo's. They are much heavier, so I figure that is where i lost the mileage.

[jro909]

my mileage went to shit.....ended up being brakes dragging and now all is good

[04SILVRADO]

A lot of areas go to a winter blend gas at this time of year. You will lose a couple of mpg's because of this crap!

[rdnkcpa]

My truck is a 2004 1500 4x4 ECSB. 5.3L LM7 V8, 4 Speed auto, 3.73 rear with 126K on the odometer. Last year I did a tune up and the best mileage I can get now is about 16.5 MPG. The best I have ever gotten was just about 18 when the truck was new and on the factory tires. Once I switched over to Bridgestone Revo's, it dropped immediately by 1 MPG.

 

When I pulled the plugs out at 119K, they were done. I replaced with AC-Delco's and it runs smooth as silk. I plan on changing the transmission fluid and front & rear diff fluid, hopefully that will help a little.

 

Last summer I took it on a long road trip. I watched my speed, tried not to faster than 70 and I was really surprised I did not break 17MPG.