BII 4.0l MPG's ???

[jollykreiger]

I finally adjusted for my speedometer (%18 off) and calculated my gas mileage.

At 70-75mph I got 16.5 mpg. Does this seem about right?

I did go from 1000' up to 2500' elevation and back down 4 times. But the rest was smooth sailing on the freeway.

The rig is a 84' with a pushrod 4.0l, fm145 (5 speed) unknown T-case and axle ratios. I pretty sure the axles are the stock 3.45, but almost feel lower. Second gear tops out around 45 or 50 mph. Tires are 235/75 winter pikes and there is a 3 in body lift, no suspension changes.

For some reason I thought I would get a little better. My aerostar with the same motor and 4spd auto got 17 mpg when I had it and 15 now that my mom has it (lack of maintenance I think).

Any thoughts out there or is this about average.

 

[Shoddy Cologne]

That doesnt sound terrible. My 2.9 would get 15 at best and its a turd.

Sent from the wrong side of town using Tapatalk

 

[adsm08]

The 4.0 has almost always struggled to get above 16-17 MPG. The batch-fire ones did better than the SEFI ones, and things are generally worse now that there is corn in the gas (cars don't like corn). 16.5 doesn't sound unreasonable. I haven't really bothered to check the MPG on my BII since the swap, but I haven't even run two full tanks through it yet.

 

[lil_Blue_Ford]

Yea, that sounds about right. My 4.0L in my choptop is getting around 13 mpg at last check. A bit disappointing since the 2.9L in it was getting around 17 mpg. But the ability to use O/D and that it doesn't fall flat on it's face in 4th is worth it.

 

[4x4junkie]

A lot of it is probably the gearing if you're running 3.45s with 235/75R15 tires (3.73:1 would be better).
I believe winter tires have a lot more rolling resistance then all-season or even all-terrain tires too, so that's probably a factor as well.

Slowing down to 60-65 will likely boost your MPG by15-20% or more too.

 

[jollykreiger]

So I did some more research and now believe I have 3.73 gears.

I took an adjusted speed reading in 1st gear while hitting redline (I know not good for the motor) and got the final ratio. Should be 3.76 trans ratio in 1st with 4,900 rpms at ~29.5 mph and using 28.8" (I went with 28.5") tires. Using all that in the rocky-road.com mph calculator inputting common ratios. the only one that lined up was 3.73s

I do love the power that I have, I can pull every one of those grades in 5th almost as well as I could in my old 5.0l mustang.... almost.

When I took it hunting and was trying to figure out my speedo I kept outrunning my buddy's sidekick even though I had the trailer. At one point on a hill I asked him why he was falling behind and he said he was going 80 and I was pulling away

I am driving to work the next few days so that is all 60-65mph but Im not convinced there will be much of a change. Im barely on the throttle at 75. But I will see, I always fill up and check my MPGs no matter what Im in every time I get gas... except my scout II and full size bronco then I just close my eyes and pray it doesn't take too much.

 

[lil_Blue_Ford]

Guess I should have mentioned, my choptop is running 4.10 gears and 35" tires, lol. And I know my odometer is off by a bit.

 

[alwaysFlOoReD]

If you have a smart phone, use an app for speed calculation. I use one called DigiHUD on my android.

 

[trail B2]

When I checked mine years ago it was 18 at 55 so seems about right.

 

[jollykreiger]

I was gonna check my 60 mph mileage, but my buddy called to pull out a stuck one ton dodge at midnight and I completely forgot to check it when i got gas in the middle of the night, pulled out my buddys cherokee fine, that we used to pull the one ton.

We had to leave everybody else cause they thought we couldnt do it with a measly cherokee and B2 so they didnt even ride along. Left 4 other stuck trucks out there, and we coulda pulled them all out, except one really burried dodge.

 

[wildbill23c]

Yep the 4.0L V6 engines got horrible fuel economy across the board, didn't matter what brand vehicle, they were not economical LOL. Makes the Bronco 2 feel faster though LOL.

 

[4x4junkie]

20-21 is about what I get with my '94, even in it's current (lifted) state on 33" tires... I wouldn't really call that "horrible"... Even more-modern trucks aren't doing much better than these old 4.0Ls, maybe 1-2 MPG or so.

Again your mileage will certainly be in the crapper if you like to speed though, aerodynamics are not a strong suit of pickups/SUVs (the above figure is @ 60-65 MPH)

 

[Nerdrage88]

My b2 gets like 16 city 18 highway with 3.73s and 235s. I'm going to keep the 2.9 but I think I'm doing to 410s and hopfully a m5od will help.

 

[blackbronc]

Damn I feel lucky. My BII with 2.9 5 spd was getting 25 plus highway only with 4.10s and smooth 33"BFG ATs. The pacesetter headers made a noticeable mileage gain when I installed them. Running new 33" MTs mileage came down noticeably and I've never ran it long enough on the highway with them to tell how much. Tire pressure and aggressive tread can make a huge difference. Aired down it won't even pull 4th at any speed.