3.0 Turbo Diesel in a JLU - Page 4 - JeepForum.com
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post #46 of 56 Old 03-19-2021, 05:38 PM Thread Starter
Axhammer
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I filled up my tank yesterday, and did a manual calculation that determined I got 24 MPG for the last tank of gas. Most of my driving for this tank was rural roads, 45-55 MPH, not much highway driving where 60-70 MPH is the norm. This would indicate wind resistance is a big factor, so I kinda agree that the added wind resistance from the taller lift/tires on the Jeep are hurting my fuel economy more than the gearing.

The next time I have to do a road trip on the highway, I plan on reinstalling my OEM wheels/tires, and reset the speedometer for the smaller tires. This will restore the original gearing, and test the theory. I know that when I put a leveling kit on my all stock 2017 JKU Sahara it took a pretty good hit on MPG from raising the Jeep 1.5” in the front.


Why do I own a CJ? I like to “Balance the wrench and the steering wheel”
1985 CJ-7 Sebring Red, White hardtop, 284 CID inline six (4.7) TF 999 auto
2020 JLU Black, Black hardtop, EcoDiesel, 35’s on 2” Mopar lift
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post #47 of 56 Old 04-04-2021, 02:42 PM
RockWoRM
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Quote:
Originally Posted by Prot View Post
That’s a pretty big hit in fuel economy. For some reason I though the diesel would have only a 1 or 2 mpg loss of fuel economy.

I wonder if regearing it would restore most of the loss.

And before somebody says it’s a Jeep, if you want good fuel economy get a Prius, it’s more of the decreased range than the expense of a reduction in fuel economy.
FYI/FWIW to you and axhammer. I was getting 27/28 mpg on my 1500 Eco on the OEM radials. Wore those out and swapped to a better AT for off road situations and the load rating. The more aggressive tread, even tho they ride nice and are quite quiet, I lost 4-5 mpg just by swapping meats.
I would think the off road tire, combined with the aero dynamics of a Jeep would be the culprit here. The extra resistance of the off road tire, tells the truck/tranny to drive in 7th gear way more than before. I usually have to 'coax' it into overdrive, even on flat smooth highway. The combination of that knocks the mpg way down.
Anywho, still waaaaaay better than my old '06 Ram hemi that only got 13/14!

'05 LJR, 6sp, RC long arm w/MC 6" coils, 5.13 D44's w/chromo shafts, MetalCloak fenders/sliders/body armor, 37x12.50 MTR's, Warn 9.5, RockHard swing out w/full spare. <><
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post #48 of 56 Old 04-04-2021, 07:44 PM
Prot
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Quote:
Originally Posted by RockWoRM View Post
FYI/FWIW to you and axhammer. I was getting 27/28 mpg on my 1500 Eco on the OEM radials. Wore those out and swapped to a better AT for off road situations and the load rating. The more aggressive tread, even tho they ride nice and are quite quiet, I lost 4-5 mpg just by swapping meats.
I would think the off road tire, combined with the aero dynamics of a Jeep would be the culprit here. The extra resistance of the off road tire, tells the truck/tranny to drive in 7th gear way more than before. I usually have to 'coax' it into overdrive, even on flat smooth highway. The combination of that knocks the mpg way down.
Anywho, still waaaaaay better than my old '06 Ram hemi that only got 13/14!
That seems to suggest maybe some of the loss could be reclaimed with regearing .

Using the calculator I posted previously, OP should swap the 3.73 gears for 4.10 gears. I recommend Yukon gears and while it is apart install Yukon zip lockers in both differentials. They are very similar to ARB air operated lockers.

2014 JKU Copperhead Pearl
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post #49 of 56 Old 06-11-2021, 08:11 PM Thread Starter
Axhammer
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I swapped my stock wheels & tires on and made a road trip today. I topped off yesterday so I could do a manual fuel mileage check today. Driving 65 to 80 MPH on the freeway, I stopped for fuel after 371 miles. The tank took 15.2 gallons to top it off.

371/15.2= 24.2

When it was new and all stock it got 32 MPG on the freeway.

With the 2” lift and the stock wheels & tires it got 24 MPG.

With the 2” lift and 35’s it got 22 MPG.

I don’t think re-gearing from 373’s to 410’s will make a difference, I think it’s more about wind resistance.

I’ll post a picture of the speedometer & tachometer from today, showing 2100 RPM @ 79 MPH.
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Why do I own a CJ? I like to “Balance the wrench and the steering wheel”
1985 CJ-7 Sebring Red, White hardtop, 284 CID inline six (4.7) TF 999 auto
2020 JLU Black, Black hardtop, EcoDiesel, 35’s on 2” Mopar lift
View my Pontiac in my profile
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post #50 of 56 Old 06-12-2021, 07:04 PM
Prot
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I think you are right with regard to wind resistance but lower gearing / higher numerical gears makes it easier to overcome resistance, whether it is from increased tire size and weight, towing a trailer, or increased wind resistance.

That being said, I don’t think you would make up all of the loss in fuel economy and might regain only 1 or 2 mpg.

The deeper gearing also translates to less strain on the transmission and possible better heat management.

I know the gasoline models are a different animal, but my 2007 JKU with an automatic and 315/70-17 tires had 5.13 gears. That combination worked to overcome the mismatch of the anemic 3.8L and a transmission that was ill suited for the task.

In my 2014 JKU, I have the 3.6L with automatic and 315/70-17 tires. I went with 4.88 gears which are ok, but 4.56 would have been fine. The 4.88 gives me more sports car like Performace on the street, a bit easier time towing my enclosed trailer, and opens up the option to go to a bigger tire if I wanted. I have had 35’s on it since new and I am now at 93,000 miles, so 37’s aren’t going to happen. My fuel economy isn’t too bad on the highway but sucks horribly in the stop and go low speed city driving that I am doing more and more of.

Me getting kind of up there in mikes is what keeps me watching what is going on with JL’s

2014 JKU Copperhead Pearl
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post #51 of 56 Old 07-25-2021, 10:51 AM
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I bought one it’s sick!!
Quiet, pulls hard, Willy’s badging looks great!
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post #52 of 56 Old 07-25-2021, 10:54 AM
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Wife drove while I slept what I could being thrown around hard braking, hard acceleration.
Every time I looked we were on governor (97)
We averaged 29mpg from PALM SPRINGS to Las Vegas
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post #53 of 56 Old 07-25-2021, 11:00 AM
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I use Mobil 1 6 quarts and a $15 oil filter from Jeep dealer.

I’m at 15,500ish miles added 8 gallons of def at $2.00 a gallon at most truck stop pumps.

Averaged $27 mpg mixed use.

87.6 miles off-road round trip from Hemet, Ca. To Big Bear climbed side of mountain used 3.5 gallons total better mileage at low speeds.

Non of my Diesel Jeep’s since 07’ or my Dodge Cummins sine 91’ have ever had emissions problems.

The other big two don’t run as clean as mopar!
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post #54 of 56 Old 08-02-2021, 01:54 AM
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Im thinking about getting another jeep again. Does anybody offer a lifetime warranty on these? My neighbor picked a lifetime warranty for his cummins from the dealer in ID. If so I am prob gonna go this route with the factory lift so i can stuff 37s in it. Ive been rocking a 73fj 40 since I got rid of my xj a decade ago but I want more comfort creatures now a days.
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post #55 of 56 Old 08-03-2021, 05:46 AM Thread Starter
Axhammer
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You can buy an extended warranty through Mopar, either when you purchase it, or later if you like. I didn’t, because I figure it under warranty for 3 years or 36k, so I am covered for now. I’ll probably buy one when that factory warranty expires. An I may buy it through my local credit union instead of Mopar, but I will do some research first and make sure whatever I get, won’t be voided if I make any mods, like the Tazer got setting my Speedo.

Why do I own a CJ? I like to “Balance the wrench and the steering wheel”
1985 CJ-7 Sebring Red, White hardtop, 284 CID inline six (4.7) TF 999 auto
2020 JLU Black, Black hardtop, EcoDiesel, 35’s on 2” Mopar lift
View my Pontiac in my profile
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post #56 of 56 Old 08-03-2021, 08:24 AM
cranbiz
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Lifetime Mopar warranty went away in either 2018 or 2019. The longest I have seen is 8 years and I believe 125,000 miles. Warranty starts at delivery so in reality, it's a 5 year extension.

02 WJ Laredo, heavily optioned but stock
12 JK, 3.5" Teraflex/Franken lift, Bilstein 5100's, BFG KM3's 37x12.5/R17
17 WK2 Trailhawk
KN4BBA
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