08' silverado, 12mpg??

[DaMoNe6969]

Just aquired an 08' Silverado with 5.3 (all aluminum) vortec and active fuel management, just under 90,000kms

over the last couple weeks its been getting a consistent 12 mpg. Mostly highway, very light foot

Idles ok, lots of power. Brought it to the dealership (ses was on) they told me it was evap and that was the problem, $400 later, evap was fixed but then they told me it wouldnt effect fuel economy

Brought it to a trusted mechanic, he couldnt find anything wrong.. he said the O2 sensors were reporting slightly lean but not nearly enough to warrent replacing

I know these engines are capable of nearly twice the mpg im seeing, Ive still got the dealership window sticker that claims 27mpg highway

Whats everyone else getting for fuel economy??

[cf1]

Originally Posted by DaMoNe6969

Just aquired an 08' Silverado with 5.3 (all aluminum) vortec and active fuel management, just under 90,000kms

over the last couple weeks its been getting a consistent 12 mpg. Mostly highway, very light foot

Idles ok, lots of power. Brought it to the dealership (ses was on) they told me it was evap and that was the problem, $400 later, evap was fixed but then they told me it wouldnt effect fuel economy

Brought it to a trusted mechanic, he couldnt find anything wrong.. he said the O2 sensors were reporting slightly lean but not nearly enough to warrent replacing

I know these engines are capable of nearly twice the mpg im seeing, Ive still got the dealership window sticker that claims 27mpg highway

Whats everyone else getting for fuel economy??

I have an 2006 4.3 can only get 20 mpg hiway.

[j cAT]

Originally Posted by DaMoNe6969

Just aquired an 08' Silverado with 5.3 (all aluminum) vortec and active fuel management, just under 90,000kms

over the last couple weeks its been getting a consistent 12 mpg. Mostly highway, very light foot

Idles ok, lots of power. Brought it to the dealership (ses was on) they told me it was evap and that was the problem, $400 later, evap was fixed but then they told me it wouldnt effect fuel economy

Brought it to a trusted mechanic, he couldnt find anything wrong.. he said the O2 sensors were reporting slightly lean but not nearly enough to warrent replacing

I know these engines are capable of nearly twice the mpg im seeing, Ive still got the dealership window sticker that claims 27mpg highway

Whats everyone else getting for fuel economy??

your evap problem may be due to over filling the fuel tank. being a 2008 this emission device should be warrantee . if in canada ? with no DTC ???

I don't see how this 27MPG is possible. I have heard from owners of the newest silverado trucks getting 22 MPG.


what fuel are you using ?

It is possible the ETC is out of range causing the injectors to stay open too long , air filter/maf dirty , replace plugs.

[DaMoNe6969]

the bumper to bumper warranty ran out a short while before I got the truck, so Only powertrain left (good for $hit)

Id never expected 27mpg, thats just what the window sticker says, But I was thinking in the neighborhood of 20mpg and Ide be happy, considering I live on an acreage and %75 of my driving is highway..

I use regular octane (87) but will only get fuel from Shell or petro-canada..

Ive tried using mid and premium (shell premium(91) has no ethanol) but it didnt make any difference at all

Iridium plugs are supposed to be good for 100,000 miles, my mechanic said they looked fine and he wouldnt replace them. Put in a new air filter at last oil change, and my mechanic cleaned the maf and intake when I brought it in, to no avail

[j cAT]

Originally Posted by DaMoNe6969

the bumper to bumper warranty ran out a short while before I got the truck, so Only powertrain left (good for $hit)

Id never expected 27mpg, thats just what the window sticker says, But I was thinking in the neighborhood of 20mpg and Ide be happy, considering I live on an acreage and %75 of my driving is highway..

I use regular octane (87) but will only get fuel from Shell or petro-canada..

Ive tried using mid and premium (shell premium(91) has no ethanol) but it didnt make any difference at all

Iridium plugs are supposed to be good for 100,000 miles, my mechanic said they looked fine and he wouldnt replace them. Put in a new air filter at last oil change, and my mechanic cleaned the maf and intake when I brought it in, to no avail

I would replace the plugs at 50,ooomi. check all for proper color . If color off check compression.


replace the ECT sensor not expensive or hard to do.

your fuel 87 octane shell is what I use . I get with my 2000 5.3L 19 MPG in the summer ...you should get 22 MPG..

you have a problem with this 12 MPG ..

I also use techron injector cleaner ONE 16 OZ bottle /tank .I at this time add 3-4 OZ of marvel mystery oil to fuel ..this all cleans and lubes the entire fuel system. replacing the fuel filter at the 30-40,000mi mark is also a good idea..

INjectors may be sticking dirty etc..

[DaMoNe6969]

well i just thought Ide update. Had the truck back to the dealership twice now. Super injection purge, cleaned maf/throttlebody/intake.. Still 12 mpg (at best)
Beyond that, the dealership said there was nothing wrong with the truck and it seemed to be running fine. They said no need to change the plugs

Typical "technician" If the engine light aint on, theres nothing wrong. But it seems to me, all their testing is done at idle. Could this be a problem only showing up under load, that maybe the tech's arent picking up?

maybe I just got a lemon!

[j cAT]

Originally Posted by DaMoNe6969

well i just thought Ide update. Had the truck back to the dealership twice now. Super injection purge, cleaned maf/throttlebody/intake.. Still 12 mpg (at best)
Beyond that, the dealership said there was nothing wrong with the truck and it seemed to be running fine. They said no need to change the plugs

Typical "technician" If the engine light aint on, theres nothing wrong. But it seems to me, all their testing is done at idle. Could this be a problem only showing up under load, that maybe the tech's arent picking up?

maybe I just got a lemon!

the check engine light will show if a componet failed. could be the O2 sensors are out of spec causing the increased fuel demand.

the knock sensor may also be out of spec retarding the timing..

sometimes the dealership tech's get like a deer in the road when looking at the idiot lights on the diagnostic machine !

that vehicle should get 20 mpG

[MT-2500]

Originally Posted by DaMoNe6969

well i just thought Ide update. Had the truck back to the dealership twice now. Super injection purge, cleaned maf/throttlebody/intake.. Still 12 mpg (at best)
Beyond that, the dealership said there was nothing wrong with the truck and it seemed to be running fine. They said no need to change the plugs

Typical "technician" If the engine light aint on, theres nothing wrong. But it seems to me, all their testing is done at idle. Could this be a problem only showing up under load, that maybe the tech's arent picking up?

maybe I just got a lemon!

If gas mileage is that bad a good factory trained dealer tech should be able to find the problem and yes sometimes it has to be road tested.
They should have the computer equipment to drive it and check engine running on the road.

Not all dealers have or use factory trained techs.
That is where you might get the wash boy or flunkie or runner or goofer playing tech at you expense.

Ask the dealer to for a factory trained tech on engine running systems to work on your car and check it out.

If they refuse ask for your money back and find a dealer that will.

Or you can just find a good repair shop.

Check around Ask around
Word of mouth.
Family friends coworkers neighbors business people and delivery people.
Mailmen and parcel delivery people get around and notice a lot of stuff.
Even a good parts house knows what shops are good and not good.
Chamber of commerce and better business bureau and city hall.
If you find a good referral to a repair shop go look them over and talk to them.
Look for a clean looking busy place with nice people running it.
Ask a few questions and ask about their qualifications and training.
Not all places have trained tech/mechanics.
If they do not find a place that does.
Even all dealers do not have all trained techs/mechanics.

Good Luck

[777stickman]

What was the MPG up until "the last couple of weeks"?

Are you sure that you're computing the mileage correctly? Such as, not miles per liter or kilometers per gallon.

Might also check the accuracy of the odometer over an extended known length of trip.

[ar00200]

Originally Posted by DaMoNe6969

Just aquired an 08' Silverado with 5.3 (all aluminum) vortec and active fuel management, just under 90,000kms

over the last couple weeks its been getting a consistent 12 mpg. Mostly highway, very light foot

Idles ok, lots of power. Brought it to the dealership (ses was on) they told me it was evap and that was the problem, $400 later, evap was fixed but then they told me it wouldnt effect fuel economy

Brought it to a trusted mechanic, he couldnt find anything wrong.. he said the O2 sensors were reporting slightly lean but not nearly enough to warrent replacing

I know these engines are capable of nearly twice the mpg im seeing, Ive still got the dealership window sticker that claims 27mpg highway

Whats everyone else getting for fuel economy??

My experience: I have an 08 Extended Cab 4x4 LTZ with the 5.3 AFM (LMG) engine - acquired with 60000 km on the clock. I live in hilly country in Eastern Canada and so far in 6000km of driving , my best fuel mileage (on a tank fill up) has been just over 22mpg on the highway. The worst I've gotten is just over 17 mpg (tank fill up) with an overall average of 19.4 mpg.

[4x4junkie]

Most likely not your problem since you indicated having plenty of power, but a slipping transmission can cause poorfuel economy.

if the vehicles was ever attached to a port tuner it can effect fuel economy if not properly set up, even though most manufacturers report and increase after using their tuners.

Sparkplugs, Air filters, fuel filters, leaking gas lines, tire size, tire pressure, Maf sensor, dirty throttle body, or just internal alterations to the motor to increase HP in general can cause fuel efficiency issues.

it may be that your vehicle is set in the tow or haul mode and not switching out of it. I know if i use the tow haul mode on my silverado i get approximatly 12.5 MPG on highway however if it is off i get 16 or better, and i have a 6.0L vortec in my 2000 silverado 2500 LT extended cab. Which is due a tune up, weather permitting.

[4x4junkie]

However the ONLY time i have used the tow/haul modes was when I am pulling a 26 foot 5th wheel camper trailer, or my car hauler trailer.

[DaMoNe6969]

The fuel economy has been unchanged since I got the truck from my dad who's owned it since new. He didnt pay any attention to the fuel economy so he doesnt know if its always been bad. The truck is also completly stock and never been touched other than maintainance and dealership repairs.

Tow/haul light has never been on, unless Ive turned it on for towing. I dont know if it can come on without the light or not? Seems to be shifting fine, at proper points anyway. I would probably notice if it was shifting at higher rpms or slipping.

I think I will bring it back to the dealership and ask for a factory trained tech, as mentioned. I'll also request they road-test it.

My dad had a fair amount of problems with the truck in its first year and towards the end, he was really losing his patience with the techs, and service managers. I think this could be affecting the service that im getting, Im begining to think its possible that they've actually caused the problems im having

[4x4junkie]

If you think the dealer you are using to service what is now your vehicle, because of issues your dad had with them casued the problem, then i would find a different dealership to service the vehicle, not to say they are the fault but because of the lack of faith you have in that place already. Remember from time to time we must reap what we sew .. we all have our good and bad days, the dealer mechanics included, and they do tend to have to deal with the lack of patience the frustrations, and more so the attitudes that most often are due to the vehicle giving owners issues in the first place becasue of their lack of attention to preventative maintenance.

I understand that is not always the reason for issues, theres also instances of known bugs that should have been recall issues as well, along with normal wear and tear due to age and mileage.

I personally would try to find a dealership or Service Technician you like and see if they can do better fixing the issue for you.

[Bob B]

Hi,
What about the rear end gear ratio?
Some trucks are set up for tow and will have a ratio that is great for towing but not for good mileage.
Bob B