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mpg 2.5l vs 4.0

MPGs 2.5 vs 4.0  

6 members have voted

  1. 1. why the 2.5 has so low MPGs compared to the more powerful but similary rated 4.0?

    • the 2.5 is just bad and can´t power a mj/xj like the 4.0 does
    • 2.5 owners have leaded right foot and push it too hard
    • Other cause

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Way back when I first got my MJ, it was a 2.5, AX5, 2WD.  Stock everything, with 205/75/15's on it.  I regularly got 23-25 mpg in it.  Eventually I started modding it....bigger tires, lift, bumpers, etc. and mileage started to decline, but was still decent.  I won't compare mine to when I 4.0 swapped it, because by that point it wasn't stock configuration at that point (33's, then 35's.....SOA, 4.56's, yadda yadda).


I will say I had a TJ with a 2.5 after that, and it absolutely sucked.  It got decent mileage putting around town, but any highway/interstate driving (which was the majority of what I did since it was my DD) and I had to have my foot to the floor just to keep up with traffic.  Worse if it was windy.  It did great wheeling though.


I guess it all depends on the kind of driving you plan to do with it.  The 2.5 is a rock solid power plant, no question there (my old 2.5 got pulled for the swap at around 190K and was subsequently swapped into another buddies MJ where it ran for several thousand miles after).  But, it ain't no powerhouse....that's for sure.

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In general, the 2.5L should return about 5 MPG better mileage than the 4.0L. There was a guy on NAXJA with a 2.5L in one of the Rocky Mountain states who claimed he routinely got 28 MPG. The 4.0L is lucky to get more than 20 MPG going downhill with a tailwind.

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I've driven numerous XJ's with the 4.0L, a good average mileage on all of those is 17.5-18mpg. One of those is an 87 Waggy I've owned for 25 years. My sons lifted 4x4 4.0L XJ , with 3.55 gears and 33x12.5 M/T tires gets about 14.5mpg . I've been daily driving an 88 MJ 2.5 4x4 5sp with 235/75/15 tires and 4.11 gears for about 5k miles and its getting right at 20mpg (average). I determined the best way to drive both my 2.5s is to rev them over 3000rpm before I shift them. otherwise they won't get out their own way. My lifted 97 TJ 2.5 5sp 4.11 with 33x12.5 BGF TA's gets about 16mpg. All of the figures are GPS to correct speedometer error. Both of the vehicles with 33x12.5 are off by 14% . The MJ with the 235's is off 4%. To figure accurate mileage on those with 33's I have to take the trip odo mileage and divide it by .86 to determine the actual miles. I just bought a 2015 JKU Rubi with 4.10 gears and stock tires (for the moment) and i did a 200 mile trip and got 22.2mpg.  Checked it at the pump. 


I've been a fleet manager for my own vehicles (wreckers) and others (school buses) for almost 30 years, I'm pretty anal about fuel economy. The little 4 banger has a lot of heart, but in my opinion the couple miles per gallon difference is not worth the difference in power.

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On the road my 2.5l has always got a few mpgs better than my 4.0l Jeeps.


Off road my 2.5l typically gets significantly better than the 4.0l, after long trail runs when the 4.0ls in the group are near empty, I've still got quite a bit of fuel left and just top it off each day.





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