2014+ Gas Mileage (MPG) Topic

Ohanacreek · January 14, 2014

Easy to correct with a Hypertech speedometer calibrator.

No AFM is load based by putting a larger tire on you are raising the gear ration making it harder for the engine to move the truck, however slightly it is enough to pass the set point at which the AFM switches V4 mode on and saves you gas money.

You can tune it all you want but the engine will not have enough power in V4 to give the same fuel economy it was designed for.

Chevy maxed the technology out to get the mileage.

Just like putting 35's on a 4banger toyo your milage is gonna tank.

DanielAcosta · January 14, 2014

No AFM is load based by putting a larger tire on you are raising the gear ration making it harder for the engine to move the truck, however slightly it is enough to pass the set point at which the AFM switches V4 mode on and saves you gas money.

You can tune it all you want but the engine will not have enough power in V4 to give the same fuel economy it was designed for.

Chevy maxed the technology out to get the mileage.

Just like putting 35's on a 4banger toyo your milage is gonna tank.

What you say is partially true. My effective gear ratio is in between two of the ratios (3.08 and 3.42) GM offers on these trucks. By correcting the tire size the ECM uses, it changes the shift points and V4 engagement. I experimented with different sizes with the Hypertech and found (as compared to stock tires installed):

1. Oversize tires with no correction gave delayed shifts to higher gears and decreased V4 use.

2. Artificially high tire sizes (example: putting in 40" when the actual installed size is 34") actually gave more V4 usage but greatly exaggerated delays in shifting. RPM would run very high before shifting, but it stayed in V4 mode almost all the time. So the ECM anticipated more load from the effective change in gearing, but also realized that under light throttle and the higher rpm, 4 cylinders were more than enough to provide the power necessary.

3. Oversize tires with correct oversize programmed in yields shifts and V4 engagement virtually the same as stock. For example, at 45mph I am just under 1,100 rpm in 6th gear with V4 engaged. How does that compare to what you see with a 3.08 or 3.42 rear end?

So obviously I ended up with option 3 above, and my mileage is almost as good as stock. Naturally there will be a slight decrease from the extra mass of the larger tires, but 19 overall after 15K miles according to the OnStar app seems pretty reasonable for a 4wd crew with 6.5 foot bed truck that is rated 16/22 and 18 overall. My worst tank was recently 8mpg during a day of rock crawling at speeds less than 5mph. My best is 24. Usually I'm right around 18-19 in town and 19-20 on the highway cruising at 80. As others have reported, if I drop the speed to about 73 or less the mileage climbs closer to the epa 22 highway rating. I have a few DIC pictures of typical mileage. My 400 mile average is usually around 20, but does drop after off-roading or hi-speed highway runs. BTW, the truck is very quiet and smooth cruising at 95, but naturally a bit thirsty at that speed. That was on the extraterrestrial highway in northern Nevada, probably the longest, most boring stretch of road I have ever been on.

Last comment: with the correct tire size calibration, my odometer error is 0.2 miles per 100 miles, which is probably more accurate than any of the stock odometers. So what I am saying is the mileage figures are accurate and corrected for the oversize tires by the Hypertech.

Bottom line is that oversize tires and a lift, even a small one like mine, will naturally decrease your mileage, but it's a small hit if you take the time to program the ecm for your mods. So if you like more ground clearance and larger tires for off-roading, go for it. Might not be very driveable if you start with the 3.08, but if you have the 3.42 or 3.73 you should be fine.

BTW, I did test drive an all-terrain, 5.5 foot bed with 3.08 rear end and 34's like mine, no speedometer correction, and it actually drove okay. It was very much like you suggested in that I saw very little V4 engagement, plus I didn't want the reduced payload and towing capacity of the 3.08. Ideally I would have bought the 3.73, but 3.42 is all that was available back in August and I was impatient, so here I am. No regrets.

Edited January 14, 2014 by DanielAcosta

Ohanacreek · January 14, 2014

I'm in sales so I'm on the road all the time, fuel mileage is within 4mpg to my 2011 SHAWD TL requiring PREMIUM GAS

Truck gets 15-18 town 21/24 hwy (75/55 mph)REGULAR GAS!!!!!

The .40 difference per gallon makes up for the 4mpg less.

I use the truck to pull no more than about 3-7k lbs max

Usually this

On a 6x12 trailer is all I have @2300lbs pulls like nothing's there even with the 3.08.

If I need to pull something really heavy I borrow dads crewcab '73 F350 with a ported/polished/balanced and bored 90over 460 well over 600hp/600lbs plenty of grunt @4gpmile though

The 3.08 can not handle the oversized tires like the 3.42 can those BFGs snuck-in in middle of the night and violently bludgeoned my fuel mileage to death with the aggressive good looking tread of a 33.6" all terrain tire.

Edited January 14, 2014 by Ohanacreek

OUSux · January 15, 2014

What speed? I'm trying to experiment between 45-60 myself.

Chris · January 15, 2014

55 if I hold 55 I will get about 21 out of the 6.0. It is a pretty fuel efficient number

Edited January 15, 2014 by Chris

lrymal · January 15, 2014

I'm getting 19mpg at about 65mph and can get that even at 70mph, but I'm really working it with minimal accelerator touch.

20 to 21mph can easily be had at 55mph average. That's with 18'' wheels and Michelin tires, not the Goodyear Wranglers.

lrymal · January 15, 2014

I'm getting 19mpg at about 65mph and can get that even at 70mph, but I'm really working it with minimal accelerator touch.

20 to 21mpg can easily be had at 55mph average. That's with 18'' wheels and Michelin tires, not the Goodyear Wranglers. I think as I put more miles on this truck, I'll get a bit more MPG as things begin to loosen up. 3000 miles currently.

I'm getting 19mpg at about 65mph and can get that even at 70mph, but I'm really working it with minimal accelerator touch.

20 to 21mpg can easily be had at 55mph average. That's with 18'' wheels and Michelin tires, not the Goodyear Wranglers. I think as I put more miles on this truck, I'll get a bit more MPG as things begin to loosen up. 3000 miles currently.

lovemytruck · January 15, 2014

Here's mine W/O winter blend fuel. 14' CC, 4WD, 5.3, 3:08, 6'6" box

New2GMC · January 15, 2014

What speed? I'm trying to experiment between 45-60 myself.

I finally got my truck!

I only have a 100ish miles on it but it seems 25 to 30 around town does real good. I took the wife out to dinner last night and did 20 miles down the highway and got 21mpg at 60. I'm sure I'll have to do the same thing and figure out what speeds get the better mpg. So far I really like the truck!

Edited January 15, 2014 by New2GMC

lrymal · January 15, 2014

weird message editing. Not sure what happened. Sorry about the multiple messages.

fondupot · January 15, 2014

my best 25 mile average was around 24mpgs. Mostly highway about 55 mph

Edited January 15, 2014 by fondupot

thewhitestallion · January 15, 2014

i drove 50-55 for about an hour and the "best last 25 miles" it reached up to 23.1 or something around there. that was all flat roads no traffic. the difference between 60mph and 70mph mpg wise, there is none. I get about the same. ranging from 17-21 on the dic.

New2GMC · January 15, 2014

Here's mine W/O winter blend fuel. 14' CC, 4WD, 5.3, 3:08, 6'6" box

I can't see it. I do see you aren't moving on the speedometer. you do a lot of idling?

Silverado Steve · January 15, 2014

Going 45 on flat ground, I got 24.6 while cruising in v-4

lovemytruck · January 15, 2014

Re: my mileage, idling will actually decrease gas mileage on the DIC. My best & average mpg is optained by normal highway, stop/go and freeway driving. I do fill with 91+ octane non ethanol fuel. From the get go ~1000 miles, my best mileage was in the 26+ range. As my handle says, I love my truck!