Horrible Gas Mileage 2005 Chevy Silverado V8

We have an '05 2wd 5.3L crew cab, 17" tires, cap, don't know rear ratio offhand. Onboard computer is accurate (based on manual checks of mpgs) and we are getting as high as 22 mpg strictly interstate at 63 mph, and over 18 mpg mixed driving local and highway on regular (87) gas. Highway driving includes mountains in western MD and relatively flat driving east of the Applachians, local is mostly flat around DC. If you are not getting at least what the epa sticker says you should get, something is definitely wrong.

Lena

Sorry I forgot to put in the bad mileage. It is only making between 12 and

13 MPG. It sounds like Lena you drive like the folks do, and we can't understand why it is doing so bad. The dealer refuses to think there is anything wrong. We just thought we would try this out in case anyone else had had a problem that we could go to the dealer and tell them to look at it.

I get about 12-13 around town. Could be sort of normal if that's the majority of driving. Also, trailer will reduce mileage.

Remember - keeping the tailgate down will get you a few miles better gas mileage due to less wind resistance. ;0

snip

Actually this is a myth and can actually increase fuel consumption slightly.

I think what you just said is a myth.

Point us to a scientific reputable study on this please.

This is just one of many.

With the tailgate up a cushion of slowly circulating air is created in the box. Air flows over the cab roof, across this cushion of air and over the tailgate. Beyond the tailgate it becomes turbulent and causes some drag. With the tailgate down the whole back of the cab from top to box floor causes much more drag than the first scenario. A hard tonneau cover offers less drag than tailgate up uncovered. A full cap with flat back produces the most drag. A hard cover that slopes from cab top, out beyond the tailgate, and nicely shaped offers the least drag. It's all about reducing turbulance behind you.

When you carry an aluminum fishing boat under a Beaver float plane the flat back is always pointed forward, and the pointy bow towards the back.

I always laugh at the fools driving around with the Tailgate down. That's a pretty popular myth, because it just seems like it's true! There's been enough studies to show that it's not. The Auto Manufactures want to get the best Mileage out of the truck, and this has been looked at. In fact if you notice, it's actually narrower in the back of the bed then in the front! This is part of getting better aerodynamics. The only things you accomplish with the tailgate hanging down is worse mileage by a bit, and of course over time the back end of the bed sides will stretch out and then the tailgate doesn't close right or worse, not at all. Seen a few trucks end up that way because of this. Back end is no longer solid.

Interesting stuff.

I get 17-23 in my 5.3 Extended cab with the 3.73 locking rear. By chance does he have the towing package? If you hit the switch on the shift knob and an amber trailer appears in your instrument panel, (long story short) this will lower your gas mileage because of the way your computer is programmed to think it is towing something even when you are not.

Eightupman

Their truck is a 1500 ton. He has the tow package option, and the it is off right now. He did say the last trip out it was suddenly making better mileage while not towing the trailer of course, and out on the interstate. They got it up to 19 MPG. So there has been improvement he just doesn't know why.

Thanks for everyone's help.