I 4 Mpg Survey

[kazam]

I've got an '87 Inline Four engine with an average of 16 Miles per Gallon.

 

Normally 91 octane is run; I have not yet found any vacume leaks.

 

I will have to check the seals at the valve cover more.

 

 

[gogmorgo]

http://www.fuelly.com/car/jeep/comanche

 

Of the three 4-cyl MJ's there, 20.6, 18.0, 20.0. The two 20's are 2wd, don't have any other info for the 18.

[mvusse]

I have an 87 4 cylinder, originally 4 speed 2wd. Converted it to 4wd soon after I got it (like a week). Kept record of my mileage cruising 75 mph down the turnpike from Cleveland to Chicago, got 19 mpg. Not too great for a 4 cylinder. So on the way back I stuck to 60 mph and got 27 mpg.

 

This is with 3.55 gears, slightly larger than stock tires (235/75R15 while the door pillar ticker specifies 205/75R15), a top gear ratio of 1:1 and corrected for tire size. This was also when I realized it need a taller gear.

 

So I picked up an AX5. First four gears are the same as the AX4, but it adds a 5th gear .85 ratio overdrive. Started ;looking for 4.10 ratio axles that the factory used with this transmission until I realized with 4.10 axles final drive ratio in 5th gear would be pretty much exactly the same as the 3.55 I have now in 4th. So I installed the AX5 and kept my 3.55 axles.

 

5th gear is gutless. Almost every uphill I have to downshift, wanting to accelerate and not take 3 minutes to do it I need to down shift, BUT, 60 mph is still 27 mpg and 75 mph I now get 24 mpg, from ~May through October.

 

Winter mileage is lower because of winter gasoline as well as snow tires. The snow tires alone make a large enough impact that I can feel while driving. When I switch back to all seasons in the spring I invariably end up speeding until I check the speedometer because I'm so used to hold the gas pedal in a certain spot. Best highway mileage I have achieved in the winter is 22 mpg, but I have never had the patience to go 60 mph yet over a large distance in winter.

 

Average mixed mileage I am hovering around 20 after three years or so, always 87 octane.

[mnkyboy]

I don't think mine ever got better then about 18mpg back when it was stockish.

 

Don't know what its getting now, I gave up on caring.

[Pete M]

I've got an '87 Inline Four engine with an average of 16 Miles per Gallon.

 

Normally 91 octane is run; I have not yet found any vacuum leaks.

 

I will have to check the seals at the valve cover more.

 

are the tires in your avatar the ones you're running now?  what trans do you have?

[randomguy310]

I had a 86 Comanche in 94 and drove it back from ky to cali LA and got 30 mpg was a 5 spd with 4.10 gears bed was loaded with stuff with a tarp over it I had the 22 gal tank and got 600 miles to a fill up. when I got home around town 15mpg was about the best it got..

[carnuck]

I got 14-18 with my '86 2wd 5 speed (4.10 axle) When I lifted 3 inches and converted it to 4x4 in '02 and drove to Ouray, CO it was getting about the same mileage until I filled up with a tank of 85 octane. Power went up and it went up to 25 mpg until the second tank after I got back to where 87 is minimum octane. I was worried about the mountains so I put in a tank of premium. Big mistake! Power went down and economy dropped too.

   I rolled over the scale at 6,000 lbs just as we were leaving WA state. 3 adults, a tool box, 3 spare tires (2 stacked on the cable under the back), camping gear, spare parts, 5 gallons of water. Only 1 gallon spare gas (outside the canopy on the bumper) 235/75/15 BFG tires.

   They all wore out on the way back because I was hit on the left front by a delivery truck and I kept switching tires about every 100 miles (cords were showing on them all when I got back)

[Oyaji]

Overall gearing is very important to highway fuel economy (probably more important than whether the engine is  4 or 6 cylinder). When reporting fuel economy you guys should mention any changes from stock tire sizes and final drive ratios.

[jpnjim]

if you can find non ethanol gas you'll get a lot closer to the mileage it was originally designed to make.

[Dadinator]

So, why do you use 91 octane?

 

In case you are not aware, the higher the octane, the harder it is to ignite.

That is why it is used in high performance engines with high compression, superchargers and the like.

 

The higher octane keeps these engines from pre-ignition (pinging or knocking) when accellerating which is harmful to internal components.

 

If your engine was not designed for high octane or if you are having a pinging problem, then you are throwing your money away using high octane gasoline.

 

The lower octane burns easier and more thoroughly creating more horsepower and usually better mpg as well.

 

I know that doesn't agree with popular belief, but that is because high compression/horsepower engines require higher octane.  Therefore people think that the higher octane makes more power.  In fact, the opposite is true.

 

I've got an '87 Inline Four engine with an average of 16 Miles per Gallon.

 

Normally 91 octane is run; I have not yet found any vacume leaks.

 

I will have to check the seals at the valve cover more.

[kazam]

The tires in the avatar are on the MJ; it too used to be a 2WD four speed.

Now it's got the AX-5 and 4WD; I'm not sure about the other gearing.

 

I generally run the 91 because I get some power with the Revs Up , and

I do not want detonation.  I'm still figuring out this engine and try to be extra safe.

 

& I get (in 5th gear) little torque, yet it's helpful for breaking on hills and cruising on pretty much dead straight --

I still get about 16 mpg.

 

It sounds like that is about right for my MJ's setup, yet I really like that 30 mpg S. CA MJ idea.

 

There is an XJ gauge cluster installed (I have not adjusted the tachometer rheostat yet,

as I have to get an external tachometer).

 

The ignition rotor and cap were replaced recently, and the wires are good.

The fuel filter should be fine; it's still due for replacement this month, for good measure.

The air filter is nice and clean.

 

I haven't checked the valves yet; I did put in a set of hotter plugs to keep oil residue build-up

in check. The hotter plugs work much better -- stay much cleaner.

Maybe a top end rebuild in the future... the crank rear main bearing looked excellent, when I was

under there changing some gaskgets/seals, etc.

 

 

...I'll keep working on it.

 

cheers

[Oyaji]

 

So, why do you use 91 octane?

 

In case you are not aware, the higher the octane, the harder it is to ignite.

That is why it is used in high performance engines with high compression, superchargers and the like.

 

The higher octane keeps these engines from pre-ignition (pinging or knocking) when accellerating which is harmful to internal components.

 

If your engine was not designed for high octane or if you are having a pinging problem, then you are throwing your money away using high octane gasoline.

 

The lower octane burns easier and more thoroughly creating more horsepower and usually better mpg as well.

 

I know that doesn't agree with popular belief, but that is because high compression/horsepower engines require higher octane.  Therefore people think that the higher octane makes more power.  In fact, the opposite is true.

 

I've got an '87 Inline Four engine with an average of 16 Miles per Gallon.

 

Normally 91 octane is run; I have not yet found any vacume leaks.

 

I will have to check the seals at the valve cover more.

 

Mostly on-target, but you miss the mark here:

 

"If your engine was not designed for high octane or if you are having a pinging problem, then you are throwing your money away using high octane gasoline."

 

Absolutely correct about the engine not benefiting from high octane gasoline unless designed for it. That generally means high compression or forced induction, which is what it takes to get the benefit from high-octane. But pinging can happen from carbon build-up in the combustion chamber (on both head and piston) or from unusual running under heavy load, and an engine in this condition would indeed benefit. If pinging cannot be controlled (by ignition timing changes via manual setting or knock sensor, or by fuel/air ratio compensation, typically by oxygen sensor feedback), short of pulling off the head and decarbonizing or gearing down, use of high-octane gasoline may be the only practical cure.

 

edit: maybe I misread you, and I merely restated in detail the very point you were making?  :???:

[Pete M]

The tires in the avatar are on the MJ; it too used to be a 2WD four speed.

Now it's got the AX-5 and 4WD; I'm not sure about the other gearing.

 

did you replace the rear axle when you converted?  if not, you likely have 3.55 gears and are burning a bit more gas while the little engine is struggling to push the bigger tires around.  and if you didn't install the proper speedo gear in the t-case, your speedometer/odometer is off and throwing off your calculations. :thumbsup: 

[Akula69]

 

 

So, why do you use 91 octane?

 

In case you are not aware, the higher the octane, the harder it is to ignite.

That is why it is used in high performance engines with high compression, superchargers and the like.

 

The higher octane keeps these engines from pre-ignition (pinging or knocking) when accellerating which is harmful to internal components.

 

If your engine was not designed for high octane or if you are having a pinging problem, then you are throwing your money away using high octane gasoline.

 

The lower octane burns easier and more thoroughly creating more horsepower and usually better mpg as well.

 

I know that doesn't agree with popular belief, but that is because high compression/horsepower engines require higher octane.  Therefore people think that the higher octane makes more power.  In fact, the opposite is true.

 

I've got an '87 Inline Four engine with an average of 16 Miles per Gallon.

 

Normally 91 octane is run; I have not yet found any vacume leaks.

 

I will have to check the seals at the valve cover more.

 

Mostly on-target, but you miss the mark here:

 

"If your engine was not designed for high octane or if you are having a pinging problem, then you are throwing your money away using high octane gasoline."

 

Absolutely correct about the engine not benefiting from high octane gasoline unless designed for it. That generally means high compression or forced induction, which is what it takes to get the benefit from high-octane. But pinging can happen from carbon build-up in the combustion chamber (on both head and piston) or from unusual running under heavy load, and an engine in this condition would indeed benefit. If pinging cannot be controlled (by ignition timing changes via manual setting or knock sensor, or by fuel/air ratio compensation, typically by oxygen sensor feedback), short of pulling off the head and decarbonizing or gearing down, use of high-octane gasoline may be the only practical cure.

 

edit: maybe I misread you, and I merely restated in detail the very point you were making?  :???:

 

:agree: The Renix engine in the 87 has never been rebuilt (as far as I know) and runs great, but when I put the diagnostic scanner on it the ping is pretty bad with 87 octane, and we were getting around 10 MPG. When we use 93 octane (or add an octane booster), the pinging stops and we get upwards of 15-16 MPG.  After looking into it for a bit, I think this only applies with the Renix engines, because the HO models do not have a separate ping sensor (but could be misinformed there).

 

Since the 89-99 conversion, mileage has varied greatly (between 15 and 21 MPG) on 87 octane, but the engine is still breaking in.

[carnuck]

The tires in the avatar are on the MJ; it too used to be a 2WD four speed.

Now it's got the AX-5 and 4WD; I'm not sure about the other gearing.

 

I generally run the 91 because I get some power with the Revs Up , and

I do not want detonation.  I'm still figuring out this engine and try to be extra safe.

 

& I get (in 5th gear) little torque, yet it's helpful for breaking on hills and cruising on pretty much dead straight --

I still get about 16 mpg.

 

It sounds like that is about right for my MJ's setup, yet I really like that 30 mpg S. CA MJ idea.

 

There is an XJ gauge cluster installed (I have not adjusted the tachometer rheostat yet,

as I have to get an external tachometer).

 

The ignition rotor and cap were replaced recently, and the wires are good.

The fuel filter should be fine; it's still due for replacement this month, for good measure.

The air filter is nice and clean.

 

I haven't checked the valves yet; I did put in a set of hotter plugs to keep oil residue build-up

in check. The hotter plugs work much better -- stay much cleaner.

Maybe a top end rebuild in the future... the crank rear main bearing looked excellent, when I was

under there changing some gaskgets/seals, etc.

 

 

...I'll keep working on it.

 

cheers

 

Just an FYI, but hotter plugs tend to make ping worse. I'm running NGK BKR6EK plugs which run clean AND no ping monster without an EGR valve.

[Dadinator]

edit: maybe I misread you, and I merely restated in detail the very point you were making?  :???:

 

Yep.  That's the one.  :thumbsup:

[AMCJeepMJ]

I've been tracking my 2wd rig's mileage for the past two years using fuelly. I drive 17 miles each way to/from work on the highway and about a mile of in-town on each trip. The highway has mild up/down hills, nothing drastic. On the highway I intentionally keep it at 55 mph with slightly oversized tires (245/70/16 on Silverstars)) and get 23 summer and 17 winter (studded 235/75/15 on Gamblers), averaging right at 20 mpg year-round.

 

Fee free to check my fuel-up history per my signature for real-world fuel economy instead of seat-of-the-pants guesswork fuel economy.

[Oyaji]

I've been tracking my 2wd rig's mileage for the past two years using fuelly. I drive 17 miles each way to/from work on the highway and about a mile of in-town on each trip. The highway has mild up/down hills, nothing drastic. On the highway I intentionally keep it at 55 mph with slightly oversized tires (245/70/16 on Silverstars)) and get 23 summer and 17 winter (studded 235/75/15 on Gamblers), averaging right at 20 mpg year-round.

 

Fee free to check my fuel-up history per my signature for real-world fuel economy instead of seat-of-the-pants guesswork fuel economy.

 

That real-world fuel economy is the only kind to pay any heed to - anything else falls short. I like the "Fuelly" site - thanks for posting.

 

You did not mention if your transmission is manual (4- or 5-speed) or auto - would you add that please? Also tire inflation pressure?

[hassyfoto]

1991 4x4 with I6 and 235 tires, I am getting 19 MPG around town. How is that comparing with the I4?

[AMCJeepMJ]

 

I've been tracking my 2wd rig's mileage for the past two years using fuelly. I drive 17 miles each way to/from work on the highway and about a mile of in-town on each trip. The highway has mild up/down hills, nothing drastic. On the highway I intentionally keep it at 55 mph with slightly oversized tires (245/70/16 on Silverstars)) and get 23 summer and 17 winter (studded 235/75/15 on Gamblers), averaging right at 20 mpg year-round.

 

Fee free to check my fuel-up history per my signature for real-world fuel economy instead of seat-of-the-pants guesswork fuel economy.

 

That real-world fuel economy is the only kind to pay any heed to - anything else falls short. I like the "Fuelly" site - thanks for posting.

 

You did not mention if your transmission is manual (4- or 5-speed) or auto - would you add that please? Also tire inflation pressure?

 

Sorry about that-

 

AX4, 2wd, 35psi summer, 30psi winter. Also has a fiberglass bed topper [canopy], and 2x 60# sand bags in the bed during winter. 201K.

[Oyaji]

1991 4x4 with I6 and 235 tires, I am getting 19 MPG around town. How is that comparing with the I4?

 

 

Pretty good - how about your highway mileage?

 

I mentioned earlier that any departure from stock overall gearing is likely more significant than which engine is in the truck. My reasoning is that for highway driving, aerodynamic drag is the same regardless of engine. Since the horsepower needed to overcome that is the same, it follows that the engine has to produce that same power no matter which type. The I-4 and I-6 are quite similar (I have read here) besides the number of cylinders, so I wouldn't expect much difference in efficiency. The I-6 would have a more internal friction but makes up for that to some degree with lower RPM to deliver the same power of the I-4; the added weight would add a bit to the rolling resistance (especially for the front tires, but not a great deal I guess).

 

I'd really like to see a comparison of 2 similar trucks but with different engines, driven over the same routes by the same driver. Can anyone here pony up such comparative figures?

[mvusse]

1987 Comanche lwb, I6/AW4 3.55 gears, 235/75R15 tires. 24 mpg at 55-60 mph is the best I ever got. Cruising at 75 I got 17 while my buddy in his XJ on 31s got 19.

 

1987 Comanche swb, I4/AX5 3.55 gears, 235/75R15 tires. 27 mpg at 55-60 mph, 24 mpg at 75 mph.

1987 Comanche swb, I4/AX4 3.55 gears, 235/75R15 tires. 27 mpg at 55-60 mph, 19 mpg at 75 mph (same truck before I swapped in the AX5).

 

Not a really good comparison because of auto versus manual. But even manual versus manual might not be a good comparison because the 6 cylinder transmissions have a much deeper overdrive gear than the AX5 does.

[Oyaji]

1987 Comanche lwb, I6/AW4 3.55 gears, 235/75R15 tires. 24 mpg at 55-60 mph is the best I ever got. Cruising at 75 I got 17 while my buddy in his XJ on 31s got 19.

 

1987 Comanche swb, I4/AX5 3.55 gears, 235/75R15 tires. 27 mpg at 55-60 mph, 24 mpg at 75 mph.

1987 Comanche swb, I4/AX4 3.55 gears, 235/75R15 tires. 27 mpg at 55-60 mph, 19 mpg at 75 mph (same truck before I swapped in the AX5).

 

Not a really good comparison because of auto versus manual. But even manual versus manual might not be a good comparison because the 6 cylinder transmissions have a much deeper overdrive gear than the AX5 does.

 

I'd be betting that the factory engineers have got the "sweet spots" of the engines dialed in with the gearing and tire choices they made. That's why I mentioned that departure from stock setup is important.

 

In your comparison, auto versus manual is important too, alright. I also wonder about the drag difference between LWB versus SWB. Are your trucks all 2wd or 4wd? (I'd guess 2wd with that economy.) You didn't mention that... I'm really surprised at the difference between AX4 and AX5 @ 75 MPH, and between MJ and XJ at that speed. Had your friend regeared his XJ for 31" tires? (I would guess so.) And did he also have an AW4?

 

Are your economy figures over a long period? (I'm guessing they are.) Pretty impressive numbers - thanks for posting.

[mvusse]

AAARGGHHHH!!!!!

 

Hit a wrong key while typing (still don't know which one) and a two page andf growing reply disappeared.

 

Short version:

 

These numbers are all on "summerish" long (300 miles or longer) highway trips, verified over multiple trips except 75 mph on the 4 speed, which was one trip all turnpike to Chicago.

 

These number are all 4wd, although the I4 short bed started out life as a 2wd truck, that lasted less than 2 weeks after I got it. As an aside, my (daujghter's) current Cherokee started out as 2wd and I have not been able to measure a definite change in fuel economy after the 4wd conversion before it moved up to 32" tires and 4.10 axles.

 

With the AX4 at 75 mph I was revving around 3000 rpm, with the AX5, but still the AX4 3.55 axles I was only revving 2500-2600.

 

My friend had not regeared, was also a Renix 4.0 and had the same automatic transmission and same axle ratio. But because of the larger tires he was revving lower than I was. His numbers were on a trip to Badlands Offroad Park (400 miles) with me following him.

 

The long bed numbers are over multiple long highway trips (as well as shorter ones), quoite a few of 300 miles or more, but a few years old before I went to larger tires, larger tires yet again, regeared and even larger tires. It currently runs 37" tires on 4.10 gears, but when I temporarily ran 32" tires on 4.10 gears I noticed I have engine problems as mileage is only about half of what it should have been with that combination. Thinking O2 sensor, but would like to know what exactly the computer is doing before I throw parts at it. Don't drive it all that much on the street anymore anyway, so no big deal.

 

The short bed numbers are over the past almost three years that it has been my main daily driver.

 

Old numbers I have from one long trip in a 1994 (HO) 4.0/AX15 Cherokee, 3.07 gears a few years back was 22 mpg at 70 mph and 21 mpg at 60. The next owner started with a full tune-up, then did some changes under the hood for better fuel economy because he was driving Ohio to Maryland and back every two weeks. He didn't state what speed, but after he got done he claims 27 mpg to Maryland and 26 mpg back to Ohio two weeks later.

 

Also 1996 Cherokee I have no consistent number between moving from 225/75R15 to 31x10.50 to 265/75R16, 3.55 axle ratio changed to 4.10, people borrowing it and not keeping the gas receipts and now my daughter who can't be bothered to keep a record of fill-ups.

 

Yes, this is the short version of what I had mostly typed before.

[Bornindesert]

I'm working on my '88 4spd 2.5L 4X4 SWB, it needs to pass emissions but it was only hair out on CO. Would be nice to have a shop truck to make part runs on that gets 18-20 or more, so I'm doing the O2 sensor, plugs, oil change and some octane boost in the gas.