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13.7 MPG in a 2009 Silverado 5.3

My father in law in june traded in his 2006 Silverado after an accident in which he felt the truck should’ve been totaled. When they put the 2006 back together they used the wrong parts(2wd) instead of front 4wd parts. So with all the incentives and his trade in he decided to get a newer truck. The only thing that’s not stock on his truck is a cap. With the 2006 Silverado he was getting about 18 MPG with the 5.3 v8. He only has about 3500 miles on the 2009 and we just installed Pennzoil Platinum 5w30 and a delco filter. For some reason that i cannot explain nor than him is why is the mileage so much less in the newer truck with the same engine. I will admit that he does get on it every now and again but that should only make a slight difference in economy than say 6 MPG. Any info or help would be greatly apreciated and thanks in advance.

Did his old truck have a cap? Those things really do affect the mileage quite a bit.

And the trucks were otherwise completely identical? You could have a 1/2 ton Silverado with a 5.3 or a 3/4 ton with the same engine and the 1/2 ton will obviously do a lot better on gas.

Also, is he just going by the computer for his MPG reading?

everything is the same between the two trucks. both Z71, both 1500, both 4WD, both 5.3 V8’s, same color and they both had the same cap installed. He kept the cap off of the 2006 and had it installed on the 2009. On the 2006 he was using the computer to calculate the MPG and is doing so with the 2009. Is it possible that the calibration of the computer could be off?

How does the 2009 compare with advertised EPA mileage figures? Is it missing the mark there?

Use the old miles driven by gallons used method and eliminate the occasional “getting on it” and see where you stand.

Compare with EPA figures for the truck and not to the other truck.

It has been my finding that a cap usually doesn’t effect mileage much. A genuine hat however will usually slow a vehicle down by 5-10 MPH, which will effect mileage.

Seriously, how many times have you been passed by a (non-Highway Patrol) driver wearing a hat? How many million times have you passed one? It’s gotta be the hat. What else could account for it?

Now removing tongue from cheek.

What is the rear end gear ratio in the new one and what was in the old truck?

Plus, there isn’t enough mileage on the new truck to even come close to the norm. Don’t rely on the computer for calculating mileage.

Fill the tank, mark down the existing mileage shown on the odometer and drive it until 1/4 full.

Refill, mark down the new mileage and deduct the old mileage from that and divide the result by the amount of fuel (gal’s) put in.

You’ll need to do this 3 times to get a average mpg answer.

The reason I ask is I have an ‘02 Tahoe with the 5.3L V8 with a 3.73 rear end and I get 13 mpg when pulling my 21’ travel trailer and 17.5 to 18.5 mpg with no trailer.

If the new truck has the 2.92 rear the mileage will be maybe 2-3 mpg more and if it has the 4.10 rear it will have 2-3 mpg less. Of course that depends on vehicle use and driving habits as well.

Not my daily driver now.

You should lose at least 3 MPG on the highway with a cap, more if it looks like an aluminum box. The shell creates a very high pressure zone over the bed. A plastic bed cover creates very little extra pressure or drag. Most shells are higher in the rear so that you can load cargo easier. The tires may be wider or larger than on the other truck.