1500 MPG highway

SkiDooNick700 · July 14, 2019

I agree with you. In theory, how wrong can the computer actually be? It should know exactly how much fuel is being used at any given second right? How do we know that our hand calculations are more accurate than the computer. We dont know how much gas is in the tank and have no idea if we refilled to the same exact same full level time after time.

Grumpy Bear · July 14, 2019

13 hours ago, SkiDooNick700 said:

I agree with you. In theory, how wrong can the computer actually be? It should know exactly how much fuel is being used at any given second right? How do we know that our hand calculations are more accurate than the computer. We dont know how much gas is in the tank and have no idea if we refilled to the same exact same full level time after time.

By statistical averaging. A 36 tank average will give you your seasonal shift and a cumulative average your life time number. 12 tanks will cancel fill variations and supply a 'spot average' good for the season and location. Do this frequently enough and you can spot the pumps cheating you.

My truck is roughly 8% optimistic at the DIC. I have nearly 100K miles of fuel records on this truck. I've done this sort of record keeping for millions of miles over decades of time and have the formal education in its use.

So yes even hand calculation on a single tank or even six is going to be less than perfectly accurate the more inclusive the data set the more accurate it becomes. Long term averages if the truth is important to you.

Donstar · July 14, 2019

One related observation is that the inclusion of mpg tracking on our instrument cluster has made us all aware of how modifications and driving habits impact our fuel consumption. Comparing scores with others who own similar vehicles is not as informative as comparing your own scores. I often do the same 100 mile drive of mixed conditions when visiting friends. Driving alone I can average 19-20 mpg. When doing the same trip under the careful "supervision" of my wife, I average 24!

Praedator · July 15, 2019

On a full interstate run on I-10 (pretty level) here in FL, I got 23.4 MPG without any stops and complete stock with V4 enabled.

This was with crappy stock Hwy tires from factory. Have 5.3L 4x4 with 3.42 rear end.

I have since disabled V4 mode, put 10 ply AT tires on (stock size) and taken the front air dam off.

I get 19-20 MPG with mostly 55-75 MPH driving since I live out in the country a little and my commute to work is not a lot of stopping and going.

I am light on the peddle and try to keep RPM's below 2K if I can help it in my accelerations.

If I feel frisky and get on it more, I have noticed my MPG goes down big time. So driving habits are the biggest factor. 24 MPG is something that can possibly happen with perfectly stock truck on hwy tires on flat commute with no stops.

Pearl2017 · July 15, 2019

2017 6.2 max tow, I was getting so-so hwy mileage ~20 since getting the truck. A few months back truck started conking out in the mornings then the cruise control quit working. The dealer tested the Injectors and found 2 were out of spec and replaced them, I think they were leaky. I got the truck back and mileage increased by around 2 mpg ever since. If I'm drafting other cars its Around 23-24 with V4 disabled and 21-22 on CC pushing air myself. And that is with a bigger heavier 285-65-20 Mich Defender tire.

Get a GPS and compare it to the speedometer at 60-80. Then you can calculate a correction for tire size. As soon as you change tires with another the circumference is different and the speedo and MPG calculation will be off. Bigger tires will lower the apparent MPG.

SkiDooNick700 · July 15, 2019

20 hours ago, Grumpy Bear said:

By statistical averaging. A 36 tank average will give you your seasonal shift and a cumulative average your life time number. 12 tanks will cancel fill variations and supply a 'spot average' good for the season and location. Do this frequently enough and you can spot the pumps cheating you.

My truck is roughly 8% optimistic at the DIC. I have nearly 100K miles of fuel records on this truck. I've done this sort of record keeping for millions of miles over decades of time and have the formal education in its use.

So yes even hand calculation on a single tank or even six is going to be less than perfectly accurate the more inclusive the data set the more accurate it becomes. Long term averages if the truth is important to you.

Well said! I have randomly taken samples throughout ownership and have come up with the range ive given. Interestingly my Trip B says 17.2mpg over the life of the truck, 51k miles. Its actually pretty inline with my own hand calc average i suppose.

SkiDooNick700 · July 15, 2019

5 hours ago, Pearl2017 said:

2017 6.2 max tow, I was getting so-so hwy mileage ~20 since getting the truck. A few months back truck started conking out in the mornings then the cruise control quit working. The dealer tested the Injectors and found 2 were out of spec and replaced them, I think they were leaky. I got the truck back and mileage increased by around 2 mpg ever since. If I'm drafting other cars its Around 23-24 with V4 disabled and 21-22 on CC pushing air myself. And that is with a bigger heavier 285-65-20 Mich Defender tire.

Get a GPS and compare it to the speedometer at 60-80. Then you can calculate a correction for tire size. As soon as you change tires with another the circumference is different and the speedo and MPG calculation will be off. Bigger tires will lower the apparent MPG.

I discovered multiplying by 1.03 (went from 275 55 to 275 60) corrects my mileage. Just divide your old and new tire revs per mile ?

aseibel · July 15, 2019

3.43 gears, 6 spd here, I get between 19-20 mgp (for a whole tank) on the highway in summer. That is with cruise set at 70-71. And that is with stock sized 18" tires. The only way I do better than 20 for an entire tank is if i have calm wind, or wind at the back.

Winter gas gets less, windy conditions gets less, driving around town gets less. It takes special circumstances to break 20 mpg for any full tank. I will get up to 22 mpg on the 25 mile trip in those same conditions.

Driving 55-60 nets the best numbers, as that is where I have hit my best ever mileage. A couple times I have broken 25 mpg for a trip. But I still can't get that for an entire tank.

Yondu · July 15, 2019

Straight highway at 70mph I get 24mpg. My average is usually around 16 though, a lot of city. My understanding is my tire size 33 vs 31.5 stock) throws my computer off and I don't use 4cyl mode much. I'm also traveling further than my computer thinks. For this reason I think a tune w/tire adjustment will help a bit.

2018 5.3 6 speed crew, 3.42. 1.25" lift, 275/60r20 tires.

300 Blackout · July 17, 2019

1500 CCSB 5.3 6L80 4.56 long tubes w/ dual 3” exhaust and x pipe. Sitting on 275/65R20 STT Pro and a front level. AFM disabled. 12mpg around town and 17-18 on the highway. Direct correlation between how thirsty she is and how heavy my foot feels. :-)

So after I installed my long tubes, I never got a tune since I have other mods on the way and the tune would be deleted within the year.

This causes the engine to run rich at fixed values to protect itself. So, yesterday, I hooked up my wide band O2 sensor which also has a 0-1 volt analog output to simulate a narrowband sensor. I ran a splitter off of that signal wire and connected each leg into the signal + in the OEM wiring harnesses for the rear O2 sensors.

My gas mileage has increased by 15-20% based on a 150 mile highway trip pre and post modification using cruise control mostly. I’m am using the engine computer for the calculations. Although the engine computer may not be accurate for actual gas mileage, it’s probably accurate to demonstrate the % of change since the pre and post modification results were obtained from the same source.

Flinthills · July 18, 2019

It is fun when the instant readings say I get 13 going up a small hill and 75 going back down. Then the numbers are just a form of entertainment

NomadicCPO · July 18, 2019

5.3 CC, 8-speed with 3.42 gears. Around town in winter ~16mpg, summer ~18mpg. Highway at 70 ~21-23. Best ever over a tank was 25mpg...and yes it was on country backroads doing 55mph.

L86 All Terrain · July 18, 2019

My 6.2L is leveled on 33"x12.5" 10 plys, it gets a combined 18mpg, but more like 16 on the hwy. It does better in town and on low speed roads when AFM kicks in. Best I have ever got it to read was 9.9L/100km (23.75 USMP) and that was on stock tires, limping home through the prairies on the first 500km on the truck. Never again did it come anywhere close to that. Anyone saying they get 22mpg+ on big tires is probably a brand loyalist, or one of those guys that will never call down something they paid good money for. Don't get me wrong, these are by far the most efficient V8 engines (5.3/6.2) on the market, but they aren't getting 24mpg unless you have the stock wheel barrow tires, a strong tailwind, and a downhill grade at 40mph.

The DIC doesn't count parked time either, so any one claiming 23-25mpg is realistically getting 17-21mpg hand calculated. Good on gas, not 24mpg. Not even my 5.3L will get that after putting on an actual truck tire. Keep in mind I live in the rolling Clay hills, so there is very minimal flat ground, and 0% concrete roads (which greatly reduce friction against the tires) all surface treatment (poverty pavement) and asphalt here. But when drive to the city in the prairies, at 75-80mph I get about 17mpg so I don't understand how people claim their trucks optimum economy speed is 70mph, when almost all vehicles are statistically proven to lose economy beyond 55mph. This is why speed limits were lowered during the gas crisis in the 70's.

madsen203 · July 18, 2019

4 hours ago, L86 All Terrain said:

My 6.2L is leveled on 33"x12.5" 10 plys, it gets a combined 18mpg, but more like 16 on the hwy. It does better in town and on low speed roads when AFM kicks in. Best I have ever got it to read was 9.9L/100km (23.75 USMP) and that was on stock tires, limping home through the prairies on the first 500km on the truck. Never again did it come anywhere close to that. Anyone saying they get 22mpg+ on big tires is probably a brand loyalist, or one of those guys that will never call down something they paid good money for. Don't get me wrong, these are by far the most efficient V8 engines (5.3/6.2) on the market, but they aren't getting 24mpg unless you have the stock wheel barrow tires, a strong tailwind, and a downhill grade at 40mph.

The DIC doesn't count parked time either, so any one claiming 23-25mpg is realistically getting 17-21mpg hand calculated. Good on gas, not 24mpg. Not even my 5.3L will get that after putting on an actual truck tire. Keep in mind I live in the rolling Clay hills, so there is very minimal flat ground, and 0% concrete roads (which greatly reduce friction against the tires) all surface treatment (poverty pavement) and asphalt here. But when drive to the city in the prairies, at 75-80mph I get about 17mpg so I don't understand how people claim their trucks optimum economy speed is 70mph, when almost all vehicles are statistically proven to lose economy beyond 55mph. This is why speed limits were lowered during the gas crisis in the 70's.

So true..

I've did the math and have tracked the last 21k miles religiously. I average 9.8-11.2% optimistic on DIC.

Also, it does count idle fuel usage. If I remote start, idle in a parking lot, or sitting in a gas line at Costco, I can watch it impact the average MPG displayed.

If I drive 65-68 with a dirt bike in the truck, I average 22.2 DIC, 20.1 hand calculated. at 75-80 with any sort of load in the bed, I'm getting 14-16 hand calculated. (6.2 CCLB). I find it is easier to drive 65 as that is a significant drop in fuel economy to shave on a few minutes from the drive.

Driving in town and to work (1 mile each way) with lots of remote starts, I get about 12-13mpg. I consider that the cost of the luxury to drive rather than walk.

swoleymammoth · July 20, 2019

On 7/17/2019 at 7:47 PM, NomadicCPO said:

5.3 CC, 8-speed with 3.42 gears. Around town in winter ~16mpg, summer ~18mpg. Highway at 70 ~21-23. Best ever over a tank was 25mpg...and yes it was on country backroads doing 55mph.

I'm getting about the same with my 5.3. Honestly impressed by the fuel mileage on these trucks considering it's a v8. My 04 Dodge 1500 5.7 got about 10-12 city and maybe 14-15 highway so switching over to this truck and seeing these numbers impressed me. Also makes me want to keep my truck mostly stock because I'm sure MPG's will plummet if I start adding a level, heavier tires, etc.