2008 5.3 fuel usage

foreverGM · February 22, 2016

Recently purchased a 2008 silverado extended cab - 5.3 1500 with HD chassis, 3.42 rear, auto trans, 40,000 orig miles. Love the truck, but hate the mileage. I know the truck is heavy at 5800 lbs, but can't get above 16mpg no matter what type of driving I do. Is this normal mpg? Has anyone out there made any improvements with their trucks mpg? Thanks

BlackZ71Silverado · February 22, 2016

Sorry to be the one to say it but you bought the wrong vehicle. Seems like your main concern is fuel mileage and the truck purchase was a mistake. Should have bought yourself a Prius or similar vehicle.

2008 Silverado 1500 HD?????? Are you sure you know what truck you bought?

dkjbama · February 22, 2016

My truck is an 08 5.3 CC 4x4 with 3.73's. I get about 11.0-11.5 in town because my commute is 3 short miles of stop-n-go traffic. At 70 mph on the highway on long trips I get between 17.6 and 18.0 depending on the wind direction with AFM disabled. If I push much past 70, mpg craters because of the wind drag. 75mph gets me 16.8-17.0 and 80 mph drops it down into the low 16s.

In town, your 3.42's might be hurting you, but not enough to justify a gear change.

If I got 15 or 16mpg overall, I would be ecstatic.

EDIT TO ADD: My tires are stock size Michelins and the truck is not lifted. If you have a lift/level or oversized tires, your MPG will suffer.

Nanotech Environmental · February 23, 2016

Recently purchased a 2008 silverado extended cab - 5.3 1500 with HD chassis, 3.42 rear, auto trans, 40,000 orig miles. Love the truck, but hate the mileage. I know the truck is heavy at 5800 lbs, but can't get above 16mpg no matter what type of driving I do. Is this normal mpg? Has anyone out there made any improvements with their trucks mpg? Thanks

I have a an 06 like this, same gears, etc. but not an HD. I can regularly get 23-25mpg (19-21 US mpg) on the hwy in the summer- On longer trips. Speed has to be kept steady, no higher than 65mph, tires need to be inflated to 45-50lbs and you have to drive like there's an egg on the gas pedal under your foot. Momentum is your friend.

In the winter its a different story. Mileage drops by 15-20% no matter what I do.(Canadian winters)

Not sure where you live, but it's still winter time, so if your in or near the snow belt, that could explain it.

Ethanol gas could also be a factor.

silveradosid · February 23, 2016

2007 1500 chev 4x4 15 in town maybe 17 on the highway

foreverGM · February 24, 2016

Thank you to those who replied to my original post with helpful answers.

My truck is 2WD, and has the original size tires inflated to the max recommended pressure. I put the vehicle up for the winter as roads are heavily salted here this time of year. This truck came from Hawaii, so I'd like to keep it as rust free as it is. For some reason the truck consistently gets about the same fuel economy (16+-) whether I drive rural/city or mostly highway. I had tried ethanol free gas in one of my other vehicles and didn't see much of a mpg improvement, not enough to make up for the increased price. I was just inquiring whether any changes to intake or exhaust system components would make a noticeable improvement and wondering what everyone else was experiencing for mpg. I know the cost of these changes would never be recouped, but it's a good excuse to change things without the other half complaining. I am a little unhappy with the mpg, but wouldn't hesitate to buy it again. Plenty of power, decent ride, sharp and GM!

As for Black Z71's response I'm sorry to say YOU are wrong. I bought the exact truck I would have chosen had I ordered it new. The lower fuel economy than I expected is not a game changer. In response to my calling it a HD- 42,870 incl. mine of 80,727 trucks on a database I checked had the "Z85 option- increased capacity chassis package". Does that make it a HD? Does in my book. Besides believing in GM products (although they do have their issues) , I'd never buy foreign - PERIOD!. Although a Prius might be a good choice for you, I DO know what truck I bought and I haul a little more than BS, so a Prius would be lacking the capacity and hauling needs I have. With 3400 posts sounds like you might mostly haul only opinions. Happy truckin'!!

dkjbama · February 24, 2016

Chill out man. Don't let him get under your skin. My truck also has the Z85. It is the handling/trailering suspension. Only difference between it and Z71 package is the shocks. The max towing package in the GMT900 is called NHT and it is the only one with stiffer springs.

GM hasn't made a "heavy half" 1500HD since the GMT-800 series. It had a special 6 lug semi-floating14 bolt rear end, a 6.0L, and 4L70E transmission.

Our trucks have a 10 bolt rear-end and a 4L60E transmission. They have a trailering package, but they aren't a heavy-half or 1500HD in any way, shape, or form.

A cold-air intake or Airaid MIT intake tube and a custom tune might get you a little better mileage, but nothing to shout from the rooftops about.

Chris · February 24, 2016

Chill out man. Don't let him get under your skin. My truck also has the Z85. It is the handling/trailering suspension. Only difference between it and Z71 package is the shocks. The max towing package in the GMT900 is called NHT and it is the only one with stiffer springs.

GM hasn't made a "heavy half" 1500HD since the GMT-800 series. It had a special 6 lug semi-floating14 bolt rear end, a 6.0L, and 4L70E transmission.

Our trucks have a 10 bolt rear-end and a 4L60E transmission. They have a trailering package, but they aren't a heavy-half or 1500HD in any way, shape, or form.

A cold-air intake or Airaid MIT intake tube and a custom tune might get you a little better mileage, but nothing to shout from the rooftops about.

The 800 heavy half 1500HD had a semi-float 9.5" with 14 bolt cover, 12 bolt ring gear, and 8 lug shafts. The LQ9 powered SS/Vortec Max 1500's got the same rear end but with 6 lug shafts

Nanotech Environmental · February 24, 2016

Thank you to those who replied to my original post with helpful answers.

My truck is 2WD, and has the original size tires inflated to the max recommended pressure. I put the vehicle up for the winter as roads are heavily salted here this time of year. This truck came from Hawaii, so I'd like to keep it as rust free as it is. For some reason the truck consistently gets about the same fuel economy (16+-) whether I drive rural/city or mostly highway. I had tried ethanol free gas in one of my other vehicles and didn't see much of a mpg improvement, not enough to make up for the increased price. I was just inquiring whether any changes to intake or exhaust system components would make a noticeable improvement and wondering what everyone else was experiencing for mpg. I know the cost of these changes would never be recouped, but it's a good excuse to change things without the other half complaining. I am a little unhappy with the mpg, but wouldn't hesitate to buy it again. Plenty of power, decent ride, sharp and GM!

As for Black Z71's response I'm sorry to say YOU are wrong. I bought the exact truck I would have chosen had I ordered it new. The lower fuel economy than I expected is not a game changer. In response to my calling it a HD- 42,870 incl. mine of 80,727 trucks on a database I checked had the "Z85 option- increased capacity chassis package". Does that make it a HD? Does in my book. Besides believing in GM products (although they do have their issues) , I'd never buy foreign - PERIOD!. Although a Prius might be a good choice for you, I DO know what truck I bought and I haul a little more than BS, so a Prius would be lacking the capacity and hauling needs I have. With 3400 posts sounds like you might mostly haul only opinions. Happy truckin'!!

What rpm are you running at a steady 60mph? It should be around 1500-1600 or so.

BlackZ71Silverado · February 24, 2016

Not trying to get under anyone's skin at all. It's just that people buy a 1/2 ton pickup and then come here and complain about fuel mileage, it's crazy. Don't buy a truck expecting small car like mpg's because you will be disappointed, just like the OP.

It also helps to post the correct information about the truck you purchase. GM didn't make an HD 1/2ton for the OP's year, it doesn't seem like he knew that and may have paid extra thinking that's what he was buying. That happens to a lot of people. There are crooks out there and they take advantage of people who don't know about the vehicle they are looking at, in the OP's case his truck. Shocks do not make a truck an HD, not even close. If that's what someone believes, they have a lot to learn and should update their 'book'.

Posting correct information when you have an issue helps narrow things down a bit when people are trying to help solve an issue. When you are corrected after posting incorrect information be thankful, don't pitch a fit.

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C3pilot · February 25, 2016

Try driving at a higher RPM range. Say like with the tow haul mode engaged when your not towing. I too had been noticing my MPG dropping, about 16.3. I read somewhere on the inter-webs that the LS motors RPM sweet spot is a little higher than where it usually sits while at highway cruse speed. So on my last 350 mile round trip I tried it, it a combo of the higher rpm while below highway speeds and cruising on the highway at a higher speed than what I normally do but I got about 17.7 MPG.

Maybe it was coincidence or I had good tailwinds or something....of course my wife says I always have tailwinds.

jmontoya21 · February 25, 2016

I did a complete fluid/tune up got about 1.5 mpg at normal driving.

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Nanotech Environmental · February 25, 2016

Try driving at a higher RPM range. Say like with the tow haul mode engaged when your not towing. I too had been noticing my MPG dropping, about 16.3. I read somewhere on the inter-webs that the LS motors RPM sweet spot is a little higher than where it usually sits while at highway cruse speed. So on my last 350 mile round trip I tried it, it a combo of the higher rpm while below highway speeds and cruising on the highway at a higher speed than what I normally do but I got about 17.7 MPG.

Maybe it was coincidence or I had good tailwinds or something....of course my wife says I always have tailwinds.

I've read a number of internet posts where guys have used that rationale. One guy pretty much wrote a whole dissertation on a VW diesel forum about driving at the engines 'sweet spot' & carried on for paragraphs using all kinds of technical terms, graphs and calculations etc. to support his conclusion.

Problem is, they are all ignoring basic math. (assuming the engine is in a good state of tune and fully warmed up) The only way to get the best fuel mileage is to have the engine run as slow as possible, under the lightest load possible for a given speed, with the lowest possible amount of wind drag and other drag.

It's that simple.

That's why hypermilers can get exceptional fuel mileage out of a vehicle.....(while annoying everyone else on the road) It's also why hybrids get better mileage as well.

An engines sweet spot will only work when the engine is heavily loaded. It will give the best mileage possible(which will still be low) when the vehicle is hauling a heavy load, or working hard for whatever reason.

If your mileage was dropping, there's something else going on.