Drop in mpg

Chevytrk15 · December 10, 2016

I have had my 2015 Silverado 1500 crew 5.3 for the past year. One of the many things that I loved about my truck was the fuel mileage. I always averaged 19 to 21 mpg. I am usually driving about 65 mph. When I got my service done at 15000 miles at the dealership I started to see a drop in mpg. I have kept my eye on it and I have taken the truck in for another service and now 6000 miles later I am still getting anywhere between 15 to 16 mpg. Nothing I do changes it. Does anybody have any of an idea on why it is doing this. The dealership doesn't have an idea. Thanks

JRL1164 · December 10, 2016

How many miles are on the truck total? Most seamfoam the intake to clean the valves about 30K. I did mine at 25K and she smoked like a train and loaded up real bad till everything got blown out.

And depending on where your located winter fuel is out and about now and effects fuel efficiency.

Sean Neilan · December 10, 2016

My 2015 5.3 has 25k miles and a lifetime average of 16.1 mpg. I've noticed a 1-2 mpg drop when the temp drops below 45-50 degrees out. These trucks seem pretty sensitive to the temp (I've noticed the drop when winter gas wasn't being used yet). I usually get high 16's-low 17's in the summer and 14-15 mpg in the winter. Don't know where you live but that could have something to do with it. Also have you been warming it up before you drive anywhere? These things chug has while idling.

Chevytrk15 · December 10, 2016

I currently have 21k miles on the truck. I've gotten gas in different states just to see if the gas in my state to see if the winter blend is a factor. Still same mileage. The change started in September and wasn't cold. F it was a 1-2 mpg difference I wouldn't care too much. But 5-6 mpg is very different and costly. And my brother actually has the same exact truck and he is still getting 19 to 20 mpg. Thanks

OldBlue61 · December 10, 2016

And depending on where your located winter fuel is out and about now and effects fuel efficiency.

Has with mine. Like the OP, I've been averaging 20-21, but recently it's dropped to 16-17. Winter fuel is out in full force around me.

Edited December 10, 2016 by OldBlue61

michaelfloyd84 · December 10, 2016

Add about 1 gallon of 121 octane to every third or fifth tank and you will be fine. I run premium in my truck year-round and my gas mileage never fluctuates

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Chevytrk15 · December 10, 2016

I have definitely been hearing about winter blend but if it was winter blend affecting my truck this much wouldn't my brothers truck be doing the same thing. And with the 121 octane. First where would I find that and does anybody else agree. Don't mean to question you but I've never heard that and I just don't want to take a chance of messing anything up. Thanks

Chevytrk15 · December 10, 2016

And in all reality I actually have to work just to get around 15 mpg. Not hard accelerating and keeping it around 65 mph

Dnt · December 10, 2016

I had a few events that caused a severe drop in gas mileage on my 16 6.2 8spd let me recount them for you.

1. Had GM Borla catback dual exhaust installed, drop in gas mileage was noticeable and went on for around 2 weeks. NOTE: turned out to be a problem with my right foot, not anything to actually do with the truck! Sweet spot in sound is above 1/2 throttle

2. Had HyperTech Max Energy 2.0 part 2000 installed. Same effect as Borla exh system you have to test out the new power LOL

3. Had Cold Air Inductions CAI installed again same result as the other 2 items for a couple of weeks..................you have to get past 1/2 throttle to get the MOAN LOL

Overall the 6.2 is getting what I consider awesome average gas mileage for a 6000 lb 4x4 with 420 HP.

Note: The Denali Dash readout for average speed calculates all idle time / remote starts that and a lot of city driving is why the overall average is so low. I really think that if i took this truck out right now and drove very carefully on a 1000 mile round trip it would produce a much closer to 30mpg than 25mpg result!

michaelfloyd84 · December 10, 2016

I have definitely been hearing about winter blend but if it was winter blend affecting my truck this much wouldn't my brothers truck be doing the same thing. And with the 121 octane. First where would I find that and does anybody else agree. Don't mean to question you but I've never heard that and I just don't want to take a chance of messing anything up. Thanks

About 121 at the dragstrip but that's just me is unleaded 121 so we won't clog anything up And 1 gallon out of 26 gallons will not hurt your truck

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Chevytrk15 · December 10, 2016

I have done none of those. Truck is still bone stock. Thanks though

Cowpie · December 10, 2016

Winter grade fuel maybe? Higher butane in winter grade fuel to promote better vaporization in cold weather. Lower mpg is a result also.

Dnt · December 10, 2016

I have done none of those. Truck is still bone stock. Thanks though

I have done none of those. Truck is still bone stock. Thanks though

I run my truck in 4whl auto mode in the rain because the back wheels are spin happy. Sometimes I forget to swap it back to 2whl drive after the rainy days for several days or once several weeks. The drag from the auto 4whl drive will reduce gas mileage by 2 to 3 mpg everytime. If I were you I would be finding me a nice muddy field and make sure the 4whl drive is disengaged! Maybe the switch or encoder has gone bad on you?

Haus_Z71 · December 10, 2016

I'm getting 10mpg here in MN with 10F weather... I would be extremely happy to have your fuel econ!

1) Temps drop really does kill the fuel econ in these trucks
2) Tire pressure drops with temps as well. Mine were down 5psi.
3) My guess is 0-30-0 type of driving is not what they test for their 'city' est mpg.
4) Remote start every morning.

I am probably getting the worst fuel econ of anyone with a 5.3L on here.. even though I have stock tires and no lift! I can't imagine if it was snowy all the time and I needed to be in 4WD. Probably would be getting 5mpg? Pretty disappointing actually..

I still get 20-22mpg highway though. I'm just not on the highway that much anymore.

Edited December 10, 2016 by 2015_Sierra

Chevytrk15 · December 10, 2016

10 mpg is definitely rough. I appreciate all the input. My main thing is I just want to make sure there is nothing wrong with my truck. And I would like be to just know why and if upgrading the octane would do anything. If 93 would bring my mileage back up