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Discussion Starter #1
I've been lurking on this site for a little bit now with an interest to put a diesel into a Jeep. Through my searching and even a couple recent threads, I read references to vehicles with a 4BT getting MPG numbers up in the 30s on the highway, but it's always been some guy that someone met on a trail ride who had said vehicle.........no real concrete details of their setup.

Do any of these vehicles belong to members here that can comment on what tranny, transfer case, gears, wheels/tire combo you are running? Or is there another source for this info I didn't find? Just gathering info for a potential project I hope to have in the not-so-distant future.

Thanks!
 

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I got about 18 to 25-27 mpg (best ever) with a Land Cruiser that was sprung over, 35's, 4.1 gears, and a NV4500 27% overdrive. The big thing I noticed regarding fuel mileage is what your cruising RPMs are. If they are near 1800 you get much better mileage than at 2100 rpms or higher.. The difference between 65 and 7-80 mph for me was drastic .

Most of the really high estimates I have seen have been fiction. The only one that genuinely got 27 mpg that I know personally was a FJ60 land cruiser with stock 3.73's, NV4500, and 33 street tires. So very fast geared.

Lee Alessi in his M715 got 27 mpg but I believe he would not drive it over 65 mpg usually. You can do that around here but it is a bummer because we have so many 8 hour stretches of highway out here, it is nice to get to places in 6.5 hours instead of 8...
 

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I kind of wondered about that (fictional MPG claims). I used to drive a Dodge conv. van with a 360 that needed some tuning and 12 MPG was about the best it would do. So anything you would drive after that seemed to get amazing mileage, even if it was only 20-25 MPG.
 

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If you are getting 30+ with 38.6" tires that is amazing. period. 24-26 is still awesome.
I think it also has to do with the fact that Lee's truck was not lifted (good choice!), keeping a relatively low profile, and that the XL's are so stiff that rolling resistance must have been very low.
 

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I think I could have gotten 30 mpg also if I kept it at 55 mph...
 

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i have a 4bta in my cj7...
3:31 gears
31 inch tires
final gear rpm at 65mph is 1500rpm
i get around 19 in overdrive
i'm not sure why?
i have used my gps to match my speed and its correct....
my motor is a reman is there a way to turn down the fuel?
could it be set up wrong?
i'm not sure...
i am sumwhat satisfied it dose get alot better mpg than a stock cj7 but if i can i would like more mpgs...
later john
 

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Discussion Starter #11
I believe a M715 has a GVW of around 8400 lbs., right? I think a Wrangler (what I would want to put it in) is about half that, so I would hope so see some increase in MPG of the smaller vehicle vs. the other.
 

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at 65mph (5th or OD) i turned 1940rpm (by calculator, not testing)
at 65mph (i used 4l60???) you turn 1632.

thats what i was wondering, why was my milage that much better and i didnt gear for "cruising at 65"

i think if you dropped gear ratio, it may help. maybe other posters will chime in. im pretty sure my buddy in the blazer has NEVER done less than 22mpg.
 

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I believe a M715 has a GVW of around 8400 lbs., right? I think a Wrangler (what I would want to put it in) is about half that, so I would hope so see some increase in MPG of the smaller vehicle vs. the other.
You are incorrect, they aren't THAT heavy. But yeah, less weight can't hurt. ;)
 

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1989 Jeep Wagoneer, 360v8, 727, stock for now,
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I kind of wondered about that (fictional MPG claims). I used to drive a Dodge conv. van with a 360 that needed some tuning and 12 MPG was about the best it would do. So anything you would drive after that seemed to get amazing mileage, even if it was only 20-25 MPG.
For the Scout:
I use 8 gal to go up to my dad's place in SerriaVista from Mesa and going home I use 6 gal. Google maps says it 192 miles one way, (my odometer says 200), so thats 384 miles using 14 gal= 27.4 mpg at or near 65mph.
 

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Your jeep should get over 30 mpg.

My 78 Blazer did 19 mpg pulling 5000 lbs about 600 miles. nv4500, 70 mph, 33" bfg AT, 4.56 gears.

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33" ATs, 3.73 gears, about 23 - 24 mpg

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36" x 12.5 hummer tires and 4.56 about 22 mpg

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38.6" LAVs and 4.56 gears 25 mpg

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1986 4bt rebuilt, nv4500, 14 bff, d60
 

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My Stock CJ with the T5 would get 18-19 mpg with 32" BFG muds. You should be able to get alot better than 19mpg. I am in the midst of finding a 4BT for a CJ build so I am hoping it will get in the upper 20 to 30 mpg.
 

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Discussion Starter #17
You are incorrect, they aren't THAT heavy. But yeah, less weight can't hurt. ;)
I guess I should clarify, I found a couple sites stating the GVW for the M715 being 8400 lbs. (http://home.off-road.com/~m726/specs.html). The curb weight is 5500 lbs.

I'm finding a YJ Jeep is ~3000 lbs. curb weight. Pushing 2500 fewer lbs. of metal down the road should let the engine run easier.

As far as the guy with the CJ getting 19 MPG, that sounds pretty low if 30+ is possible in YJ. A CJ is lighter than a YJ by about 300 lbs. (both stock).
 

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its not the weight. its the gears. ive said it before, most gear wrong. and unless someone posts something substantially different, it seems the guys that have higher MPG have higher (numerically) gears, and are also in search of less performance increases. but thats an informal UNscientific survey.
 

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Had my '67 Dodge Town Wagon [2.6 tons empty] loaded to the eyballs with tools, parts, scrap steel and the kitchen sink, pulling my Chevy LUV truck loaded with tools, parts, scrap steel and the bathroom sink. Hauled it all 600 miles from Nor Cal to So Cal, including some pretty drastic mountain driving. Average 50-55 mph and thinking I'd only driven 500 miles I calculated it out to 19.8 mpg. Figuring it correctly it came out to about 24 mpg over 600 miles.

My normal mpg running empty seems to be in the 30's, still have to crunch the numbers.

4.1 gears, 2WD, NV4500, 29" tires, stock engine no tweaks [yet....].
 
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