Why are the Eco Diesels getting different MPG's

[NKara]

Part 1:
All JL/JT with the 3.0L Eco Diesel have stock 3.73 gears. There has been nothing done to the exhaust system or emission systems.
There are 3 JLU's and a JT all doing 60MPH on the highway over relatively flat ground.
1) 21JLURD w/ stock tires and gears(KO2's 32.7in (285cm)) and a 3.5in lift: Averages 25MPG's.
2) 21JLURD w/ 37in KM3's and a 3.5in lift nd stock gears: Averages 23MPG's
3) 20JLURD w/ 37in KM3's and a 3.5in lift, w/ 4.56 Gears: Averages 27MPG's
4) 21JTD w/ 33in KO2's and stock height. Weights about 900lbs more than a JLURD: Averages 30MPG's

Jeep (3) 20JLURD when it was stock, 32.7in KO2's, Stock Height would get 30MPG's
Jeep's (1,2) 21JLURD when it was stock, 32.7in KO2's, Stock Height would get 25MPG's

Part 2:
If you compare the window sticker of a 23JLURD and 22 JLU Sport S Diesel
The 23JLURD advertises 26MPG Highway, 21MPG City, w/ an Average of 23MPG
The 22JLU Sport S Diesel advertises 29MPG Highway, 22MPG City, w/ an Average of 25MPG
They both have the same engine, same gear ratio 3.73, same transmission, and same gear ratio on the Transfer case.
The only difference is the tires
23JLURD LT285/70R17C KO2's (32.7x11.2Rx17) Weighs 57.9lbs
22JLU Sport S Diesel 245/75R/17 Michelin LTX Radials (31.5x9.6Rx17) Weighs 44.4lbs

Questions:
1) Why is Jeep 3 getting 5MPG better than Jeep's 1/2 stock?
2) Why does Jeep 4 with more weight and the now with the stock tires as the JLURD's gets 30MPGS.

I feel like there is more than just a difference in tire size to be affecting the fuel economy. Is there a specific engine tune for Rubicon's that the 20JLURD didn't get vs the 21JLURD's, possibly the same tune that is on the 21JTD? I can not find any mechanical difference between the JLURD's

Below Images:
Red Dash Jeep (3)
Green Dash Jeep (1)

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[Deleted member 59498]

Who's foot is on accelerator. So many variables seems hard to find answer.

 

[Gorilla57]

Who's foot is on accelerator. So many variables seems hard to find answer.

Exactly. I can drive my wife’s Porsche and get way better MPG and I drive it MORE aggressively.

 

[Wrangler man]

Who's foot is on accelerator. So many variables seems hard to find answer.

Ditto, thinking a big one being "rolling resistance" is the tire pressures exact? M/T VS A/T? plus the rubber compound in each style/brand tire.
Wind drag, ambient temp, road temp, tonneau cover on the JT? Vs not?
Apples to apples JL's
Apples to apples JT's
and RUBICONS always > lbs on either.
Full tank vs partial vs fuel grade, vs weight of driver/passenger. Lots of variables would need to be controlled for a true comparison
IMO

 

[Ratbert]

As others have mentioned, there are a ton of variables. Throwing out some more:

Roof racks? RTTs? Winches? Bull bars? Skid plates (more weight, but possibly more aerodynamic)? Lights?

 

[Tread4Lo]

I think it's people posting the best MPG they ever saw and them saying they get that all the time. Hell if I traveled on I-35 between Dallas and Austin, I would be in the 30mpg range with 35's. Going 85 in the middle of a pack of vehicles and no wind resistance is awesome. But get me on a 2 lane highway going 70 and I'm the only one, I'm lucky to get to mid 20's going down hill. Slow down to 60 and my MPG's will go up drastically.

Most of my tanks hover right around 20MPG's. This is with 70/30 city/highway mix. The best I saw when I had mostly highway was 24MPG's.

Rubicon's will show less, since they have more rolling resistance between tires and the locker in the diff.

 

[fourfa]

The MPG numbers in the dash just aren't accurate. Not once has mine matched what I log in my MPG app (which just takes mileage and fill volume). That's on stock tires and stock diameter calibration - stock odometer reads 0.7% low compared to GPS track of more than 100 miles. BTW GPS tracks like this have their own errors...

There's a reason that metrology is an entire career track. I don't think anyone here is going to solve this case

 

[CodeRed]

well, i dont drive all that fast, but live up in the hills...rather disappointed to see only 19 mpg recently. maybe the crappy cali fuel? all stock except for roof bars

 

[Ratbert]

The MPG numbers in the dash just aren't accurate. Not once has mine matched what I log in my MPG app (which just takes mileage and fill volume). That's on stock tires and stock diameter calibration - stock odometer reads 0.7% low compared to GPS track of more than 100 miles. BTW GPS tracks like this have their own errors...

There's a reason that metrology is an entire career track. I don't think anyone here is going to solve this case

Hopefully you realize that 0.7% low is incredibly close from the perspective of the majority of us. That could probably be rectified by adjusting your computer's settings.

 

[fourfa]

Hopefully you realize that 0.7% low is incredibly close from the perspective of the majority of us. That could probably be rectified by adjusting your computer's settings.

I do; and I could have been more clear. The point I wanted to make is the odo is accurate, the tire size is accurate, the vehicle knows precisely how much fuel it injects; but despite all that the MPG numbers it shows in the dash are inaccurate. Is it by design to make you feel better and boost NPS? (I’d assume few people actually pull out a calculator to check). Is it showing “recent” MPG instead of “since reset” MPG? Is it just vibes? No idea

 

[Ratbert]

I do; and I could have been more clear. The point I wanted to make is the odo is accurate, the tire size is accurate, the vehicle knows precisely how much fuel it injects; but despite all that the MPG numbers it shows in the dash are inaccurate. Is it by design to make you feel better and boost NPS? (I’d assume few people actually pull out a calculator to check). Is it showing “recent” MPG instead of “since reset” MPG? Is it just vibes? No idea

I'm thinking that it's only tracking the last 100 miles or so (maybe 62 if it's fundamentally metric?). If you're keeping track of it much more closely than most of us then you might have some insight into that speculation.

 

[fourfa]

Well I track every tank in the app, that’s the source of truth. I usually just glance at the reported MPG and have a chuckle at how off it is, then go back to ignoring it. So I don’t record the delta

 

[GtX]

My wife gets 20% better MPG than I do. I stopped trying to figure it out a long time ago.

 

[chrisc33]

There are so many variables at play, unless all these jeeps ran the same course theres not enough data here. I have 40s and I could get 30mpgs if the speed limit was 50mph and my commute didnt have any stops, while a stock jeep could have a stop and go commute for the same distance and may only get 22mpgs. Doesnt mean my jeep gets better mpgs, just our driving habits and conditions are very different. When Hwy driving I try to keep it @ 70mph or below. You can even draft off the car infront for a couple extra mpg(you do risk rock damage, ask me how i know lol). Combined with allowing the jeep to coast as soon as you recognize a stop ahead will help with mpgs.

 

[Shibadog]

well, i dont drive all that fast, but live up in the hills...rather disappointed to see only 19 mpg recently. maybe the crappy cali fuel? all stock except for roof bars

Remember winter blend diesel will also adversely affect fuel economy. Infinite variables here.

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