Bad 4.8l Mileage

jhoff8487 · January 22, 2008

I've got the 4.8l w/ 3.42 gears and I barely get 16 on the interstate, and if I'm extremely good, I can get 15 in the city. What am I doing wrong? I got 70 on the dot with the cruise on while on the interstate. I'm completely stock other than some nerf bars. Any ideas?

asilverblazer · January 22, 2008

It's a 4x4, they get considerably less than a 2wd. I'd bet if yours was a 2wd you would get 20mpg pretty consistently. our city mileage will never be great, your rear end gears are a little too high for that, they may also be keeping the engine a little below its peak efficiency range on the highway.

hubbycap · January 22, 2008

Yeah, I got one. What size are those wheels? You programmed their diameter into your ECM?

Zembonez · January 22, 2008

My 4.8 RCSB 2 wheel drive has averaged 16.6 so far from the day it was new until now.

unit731 · January 22, 2008

I am fearful of checking my gas mileage as I don't want to get too depressed.

pm26 · January 22, 2008

I've got the 4.8l w/ 3.42 gears and I barely get 16 on the interstate, and if I'm extremely good, I can get 15 in the city. What am I doing wrong? I got 70 on the dot with the cruise on while on the interstate. I'm completely stock other than some nerf bars. Any ideas?

Try higher name brand octane fuel. This enables the ECU to advance the ignition timing more before registering knock in the engine, and you may get better mileage, and also performance.

jrrod2004 · January 22, 2008

Did that, switched to 93, the only thing I saw/experienced was a smoother performing engine and easyiness of hammering it without noticing (more responsive)

jrrod2004 · January 22, 2008

How many miles are on the odo?

superjim · January 22, 2008

I am fearful of checking my gas mileage as I don't want to get too depressed.

That makes two of us.

Jim from Texas

todoubled05 · January 22, 2008

I've got the 4.8l w/ 3.42 gears and I barely get 16 on the interstate, and if I'm extremely good, I can get 15 in the city. What am I doing wrong? I got 70 on the dot with the cruise on while on the interstate. I'm completely stock other than some nerf bars. Any ideas?

I was running 11.8 to 13 mpg city. three days ago I switched to royal purple 5w30 and filled up with shells " v-power" 93 octane and got it up to 16.8 to 17.2 city.. highest iv ever seen.

bgrif005 · January 22, 2008

i have had my truck for a couple of months now and have only gotten 16 mpg average. In the first week I had it i did a long cruise trip of about 600 miles or so and got like 15 or 16 average. normal driving i sit in traffic most of the week, but still see about 15 or 16 average. gas mileage seems to be increasingly slightly as engine breakes in more...only 1700 miles so far.

jhoff8487 · January 22, 2008

I've actually got my stock wheels back on for winter and even during the summer when I have on my aftermarket wheels I'm using the stock tires(for now). I've got about 14k on it. I run 87 octane gas from Speedway typically. It's got Mobile 1 full synthetic in it. I knew I'd get less because it's a 4x4 but I guess I just wasn't really expecting that my highway mileage and city mileage would about equal out. It's always been this way, and it had never really bothered me before until I really started looking around on here seeing other guys with the 4.8l getting 20+ on the interstate. Before these past couple weeks I drove mostly in the city, and I've just switched to a lot of highway commuting (85 or 90%) so I was curious as to why I wasn't seeing any sort of mileage increase. It appears that it's just normal...thanks, guys.

pm26 · January 22, 2008

I've got the 4.8l w/ 3.42 gears and I barely get 16 on the interstate, and if I'm extremely good, I can get 15 in the city. What am I doing wrong? I got 70 on the dot with the cruise on while on the interstate. I'm completely stock other than some nerf bars. Any ideas?

I was running 11.8 to 13 mpg city. three days ago I switched to royal purple 5w30 and filled up with shells " v-power" 93 octane and got it up to 16.8 to 17.2 city.. highest iv ever seen.

What amazes me is that some people categorically dismiss any effect better octane or different brand of fuel would have on the mileage of their vehicle without even trying it. And sometimes it takes several tankfulls to see the results.

And if somebody thinks that by using the cheapest 87 octane they can find saves them money, they should think again. With brand name higher octane, the ignition timing can be advanced more, meaning less fuel needed and better fuel economy.

okdiscoguy · January 22, 2008

I've actually got my stock wheels back on for winter and even during the summer when I have on my aftermarket wheels I'm using the stock tires(for now). I've got about 14k on it. I run 87 octane gas from Speedway typically. It's got Mobile 1 full synthetic in it. I knew I'd get less because it's a 4x4 but I guess I just wasn't really expecting that my highway mileage and city mileage would about equal out. It's always been this way, and it had never really bothered me before until I really started looking around on here seeing other guys with the 4.8l getting 20+ on the interstate. Before these past couple weeks I drove mostly in the city, and I've just switched to a lot of highway commuting (85 or 90%) so I was curious as to why I wasn't seeing any sort of mileage increase. It appears that it's just normal...thanks, guys.

Have you thought about switching to Royal Purple in your diffs and transfer case? I got almost 2 MPG out of my 06 2500 Duramax changing everything over. I get around 20 on the highway with 60K on the ticker, but she's a diesel....

67ChevyRedneck · January 22, 2008

Is the fuel mileage drop something recent? Most places typically switch to an E10 blend of fuel in the winter, coupled with letting the truck warm up, can cause an apparent 1 to 2 mpg drop in fuel mileage. My 5.3L 4x4 typically gets 15/18 but with the cold weather, E10 fuel, and letting it warm up (I leave the tranny in 3rd until it gets up to temp) my mileage has dropped to 13/16. Just took a 100% highway trip (220 miles round trip) and only got 16. Same trip I did at least once a month in the summer/fall and was getting 18-18.5mpg.

I started a thread around the same time last year asking if possibly my o2 sensors were bad because of my mileage drop. Apparently it was just "winter driving and winter fuel."