258 mpg???

[nc wagoneer]

Ok so aw yall know I'm looking at a 80 j10 with a 360. I was talking to a local guy today after I spotted a 79 j10 I hadn't seen around before and he said it was a 258/t15/Dana 20 and he kept the hubs unlocked most of the time, he said he gets around 18 mpg daily around here on 45-55 mph backroads. What is the average you get with your 258 and what's the highest you've gotten? I plan to diesel swap the j10. Don't hate on me for this idea but I might put a 258 in if that sort of mileage can be obtained easily (read cheaply)

[RWrightPhotog]

I have never owned a 258, but I have done a lot of searching and reading and 18 HWY sounds average for a well tuned 258. Again, that's just from my own research.

[Stuka]

Back when my J10 had no lift, 31's, and 2.73 gears I could get 17 going 65mph, and 17-18 going 55 on VERY flat ground if I was easy on the throttle. That was with a TFI ignition, a Weber 32/36 DGEV carb, and a full (manifold back) 2.5" exhaust.

Driving style is very important, and if there are any hills, the mileage quickly drops.

And you should know swapping a 258 in place of a 360 isnt entirely bolt in. You will need to build new engine mounts, clutch linkage, re-pipe fuel lines (pump is on the passenger side on a 258), etc. Realitically, if you want to daily drive an FSJ, you should not be considering fuel economy at all. As just about anything will get better fuel economy.

[nc wagoneer]

This mpg is in western nc mountains (a lot of hills) I will probably do the diesel swap but was curious of 258 mpg as it would be cool to keep it AMC

[1983 j10]

If your gonna swap a six in forget the 258 and use a 4.0 and fuel injection from a xj Cherokee it will take just as much work to swap the 258 in as the 4.0 and with the 4.0 you get a better engine more efficient engine and usually yields around 23-25 depending how it's set up and driven

[Gurinski]

I thought you were gonna ask how to get 258 mpg!

[newtojeeps]

I have friends with the newer JEEPs with 4.0's and their not getting all that great of mileage 17-20. My 82 Cherokee w 258 BBd,T5/ 208/ 331's get about 18 average, cruising at 70mph on the flat I get 22-25 mpg. It don't climb the hills were a dang. But it is a DD anyway.

[Mikel]

I thought you were gonna ask how to get 258 mpg!

Easy.



And the same performance as the the 258 too! (Just kidding)

[Mikel]

I have friends with the newer JEEPs with 4.0's and their not getting all that great of mileage 17-20. My 82 Cherokee w 258 BBd,T5/ 208/ 331's get about 18 average, cruising at 70mph on the flat I get 22-25 mpg. It don't climb the hills were a dang. But it is a DD anyway.

My bone stock 97 XJ gets 17-18 MPG if I drive it under 70MPH.

[nc wagoneer]

I thought you were gonna ask how to get 258 mpg!

If you've got a flux capactior setting around call it done
If its that much work I'll go with the diesel swap as we have local biodiesel pumps and a good friend of ours is the owner of the company. I will leave this thread to post 258 mpg as I've seen other mpg threads for 360's and such but none for the 258.

[halftrac]

I live in Western NC not too far from nc wagoneer, 78 J10, 258, T-18A, Dana20, Motorcraft 2100 1.08, and MSD6. My average city highway combined is 18mpg. So yes a 258 is great in the mountains of western NC

[Stuka]

Yeah, I guess I should state that ours hills out here are not like the hills back east. Ours are just a bit taller

My J10 these days gets 10-12. But thats because it has zero compression and so its WOT on even smaller sized hills.

[nc wagoneer]

I live in Western NC not too far from nc wagoneer, 78 J10, 258, T-18A, Dana20, Motorcraft 2100 1.08, and MSD6. My average city highway combined is 18mpg. So yes a 258 is great in the mountains of western NC

I swear that people in western nc get better mpg, maybe because we aren't in a hurry to get anywhere My grandpa got low to mid 20's in his 4x4 4.3 s10 auto that most people get 16-18. Don't exactly get why we get better mpg

[RWrightPhotog]

I have always gotten a pretty steady 15 mpg up and down North Carolina hills on my trips with my 360. Just doesn't seem like the 258 would be that much of an MPG improvement. That being said I'd do a complete 4.0 XJ drive train swap in a heartbeat!

[Carnuck]

less crap in the NC fuel (no alcohol) AFAIK. I got 17-20 hwy with my '83 Cherokee and '84 J10 before going to EFI (almost done!) expect 14 -17 in town after that (BIGGER tires)