Fuel mileage finally calculated

[Ringo]

So after seeing so many post about fuel mileage but none really seem to actually do it and only assumed what the get. Here it goes, officially from a bone dry tank to fill up.

The vehicle:

1999 jeep cherokee SE. 5 speed manual ax-15 transmission. 3.07 gear ratio front rear and 3.08 gear ratio 8.8 ford rear. 0" body lift. Firestone destination AT 235-75-15 tires.

20 gallons of regular gas used. total traveled miles = 354.2 miles to engine shut down.

17.71 miles per gallon on stock ejectors.

highway speed was 74-78 mph at 64 miles a day
around town was 25-40 mph at variable miles a day

[prerunner1982]

Not bad, I would suggest bringing the highway speeds down a bit if at all possible.

[Pookapotamus]

I use the "Kilofuel" app on my I-phone to track mileage, great little app that lets you see the changes in fuel economy when you change oil or air filters, even lets you track different vehicles!

[Mudderoy]

So after seeing so many post about fuel mileage but none really seem to actually do it and only assumed what the get. Here it goes, officially from a bone dry tank to fill up.

The vehicle:

1999 jeep cherokee SE. 5 speed manual ax-15 transmission. 3.07 gear ratio front rear and 3.08 gear ratio 8.8 ford rear. 0" body lift. Firestone destination AT 235-75-15 tires.

20 gallons of regular gas used. total traveled miles = 354.2 miles to engine shut down.

17.71 miles per gallon on stock ejectors.

highway speed was 74-78 mph at 64 miles a day
around town was 25-40 mph at variable miles a day

Where did you get that 20 gallon figure? If you are going by tank size I don't think that's correct. The most I have ever got in my 20 gallon tank was 18.6 gallons and it was low enough for the engine to die.

The only accurate way to measure your gas mileage is to get the distance traveled and then how many gallons you had to put into the tank AFTER those miles were traveled.

For example if I take the 354 miles divide by the 18.6 gallon thing, I come up with 19 mpg.

[LizardRunner]

297.4 miles divided by 17.45 gal. = 17.04 MPG from a trip this weekend to Oklahoma and back. mileage was from trip odo. fuel from pump reciept.

[Ringo]

Where did i get my 20 gallon tank figure. Easy, from my Chrysler factory build sheet and a check of gallons held in my tank after removing it during a in tank filter/pump change.

[Mudderoy]

Where did i get my 20 gallon tank figure. Easy, from my Chrysler factory build sheet and a check of gallons held in my tank after removing it during a in tank filter/pump change.

Well hell, I wonder why mine won't hold 20 gallons.

[gary63]

is it dented or your pick-up is bent and won't pull all the fuel.

[nickxj94]

is it dented or your pick-up is bent and won't pull all the fuel.

Can't dent a poly tank lol! But my 94 tank is smashed in a few spots it only holds 16 gallons now

[gary63]

you are right you can't dent but you can dent a skid plate and it can push in on the tank. and you can get mud up inbetween the tank and skid and it will push the tank in.

[Mudderoy]

is it dented or your pick-up is bent and won't pull all the fuel.

Plastic tank, in good shape, factory skid, new pickup pump filter assembly. Never got 20 gallons in it when it was new either.

Does ANYONE get more than 18.6 gallons of gas in a 97+ tank? Seems like I posted about this before and no one did.

[LizardRunner]

Plastic tank, in good shape, factory skid, new pickup pump filter assembly. Never got 20 gallons in it when it was new either.

Does ANYONE get more than 18.6 gallons of gas in a 97+ tank? Seems like I posted about this before and no one did.

The absolute best I've ever done with the 2004 WJ is 18.6 mpg which I consider very good for a massaged 4.7L HO engine. before I did the work on the tranny and transfer case, including new fluids I was lucky to get 17 on the highway at a whopping 65 mph. Now I get to travel at 70+ and still get my 18 mpg unless I have a lot of up-hills to do. The tank does hold 20+ gal. of fuel though, filled it once with the little light blinking and it held 19.9 gallons by the pump's calculation. I know it wasn't empty cause it was still running when I pulled up to the pump. The green Lizard held 20.3 gal. but she was a 94 and is now back on the roads and trails with a new owner.

[prerunner1982]

Does ANYONE get more than 18.6 gallons of gas in a 97+ tank? Seems like I posted about this before and no one did.

I don't like getting my tank that empty to know for sure that it actually holds 20 gallons.

[Carves]

Plastic tank, in good shape, factory skid, new pickup pump filter assembly. Never got 20 gallons in it when it was new either.

Does ANYONE get more than 18.6 gallons of gas in a 97+ tank? Seems like I posted about this before and no one did.


76 liters is the stated metric capacity ... which is about 20.5 U.S gallons

I usually get 70 - 74 liters in it, depending on the day ... 18.5 - 19.5 U.S. gallons

Only times Ive filled it from dead empty has been with jerrycans and jerry #4 always had a bit left in it.

FWIW ... I'd reckon the tanks stated max capacity, is bone dry and without the fuel pump in there.


... as for my distance/fuel use ... 330 mile to a tank is the repeated average, highway number I've been getting for years ... I'm not interested in minute by minute mpg consumption or round town fuel consumption ... it uses what it uses then.

Less than 300 miles to a tank, on a run, and I start looking for reasons why tho. ;)

[Mudderoy]

76 liters is the stated metric capacity ... which is about 20.5 U.S gallons

I usually get 70 - 74 liters in it, depending on the day ... 18.5 - 19.5 U.S. gallons

Only times Ive filled it from dead empty has been with jerrycans and jerry #4 always had a bit left in it.

FWIW ... I'd reckon the tanks stated max capacity, is bone dry and without the fuel pump in there.


... as for my distance/fuel use ... 330 mile to a tank is the repeated average, highway number I've been getting for years ... I'm not interested in minute by minute mpg consumption or round town fuel consumption ... it uses what it uses then.

Less than 300 miles to a tank, on a run, and I start looking for reasons why tho. ;)

I bet you are right, 20 gallons without the pump etc... in there. Thanks.

[Ringo]

As an civil engineer, i do area volume calculations all day long. Owner, builder and racer since 1979.

I expect everybody here to know how to calculate fuel mileage mathematically. Not under assumptions.

Dry your tank, fill it up, take a spare can of fuel and run the bejesus out of it for three consecutive fill ups, then average it out.

And i didn't even use all UPPER CAPS.

1969 Camaro, 655 horse power at 0-60 in 1.546 seconds at 1.7 gallons in a quarter mile and a naturally aspirated small block.

How is that for fuel mileage!

[Brasscatz]

I was always told that if you run your tank until completely empty, you risk doing harm because of trash and sediment that settles at the bottom of your tank and you can clog injectors, filter, pump etc. fellas, please correct me if I'm wrong, is this true or is it a myth?

[Mudderoy]

As an civil engineer, i do area volume calculations all day long. Owner, builder and racer since 1979.

I expect everybody here to know how to calculate fuel mileage mathematically. Not under assumptions.

Dry your tank, fill it up, take a spare can of fuel and run the bejesus out of it for three consecutive fill ups, then average it out.

And i didn't even use all UPPER CAPS.

1969 Camaro, 655 horse power at 0-60 in 1.546 seconds at 1.7 gallons in a quarter mile and a naturally aspirated small block.

How is that for fuel mileage!

Could you do the volume calculation on your XJ's fuel tank? I'd like to know how many gallons that 20 gallon tank really holds.

[Carves]

I was always told that if you run your tank until completely empty, you risk doing harm because of trash and sediment that settles at the bottom of your tank and you can clog injectors, filter, pump etc. fellas, please correct me if I'm wrong, is this true or is it a myth?


More of a diesel issue than a myth I think ... Can happen in petrols tho ...

The pickup/sock filter is right at the bottom of the update XJs, plastic tank ... so if theres a bunch of sediment in there ... Im guessing you will know about it ;) .. :D

[Mudderoy]

More of a diesel issue than a myth I think ... Can happen in petrols tho ...

The pickup/sock filter is right at the bottom of the update XJs, plastic tank ... so if theres a bunch of sediment in there ... Im guessing you will know about it ;) .. :D

I've heard that the fuel is used to cool the fuel pump and if you run the tank below (a quarter tank?) you run the risk of damaging the fuel pump.

[gajeepguy]

I've heard that the fuel is used to cool the fuel pump and if you run the tank below (a quarter tank?) you run the risk of damaging the fuel pump.

We burned up several pumps in our Chevy 1500 fleet vehicles. Every time ran it completely out of gas and had to replace the pump.

Sent from my Incredible 2 using Tapatalk 2

[gary63]

the fuel pump is in the tank so it would run cooler and it would be quiter. if you run your tank down to empty alot the pump will hve a shorter life.

[4.3LXJ]

I think that is more of an issue with the plastic tanks. Those of us with return lines have constant flow

[gary63]

yes with a retune line work much better and you don't get the hot soak miss on # 3 from the fuel evaperating .

[Carves]

I've heard that the fuel is used to cool the fuel pump and if you run the tank below (a quarter tank?) you run the risk of damaging the fuel pump.


awww dammitttt ... :mad:

Now its only a 15gal tank .. :D:D:D


Its possible I guess ... going by the others, posts - and that I have replaced a couple in the TJ and the other XJ in the past.

I woulda thought they would be OK unless run for a considerable time without fuel ... but maybe not :confused:.




yes with a retune line work much better and you don't get the hot soak miss on # 3 from the fuel evaperating .

Have never had that issue that Im aware of ... Might be due to the, back the front fan set up on RHD models - and the clutchfan always blowing a bit of air past the manifolds .. :confused:

[Mudderoy]

awww dammitttt ... :mad:

Now its only a 15gal tank .. :D:D:D


Its possible I guess ... going by the others, posts - and that I have replaced a couple in the TJ and the other XJ in the past.

I woulda thought they would be OK unless run for a considerable time without fuel ... but maybe not :confused:.





Have never had that issue that Im aware of ... Might be due to the, back the front fan set up on RHD models - and the clutchfan always blowing a bit of air past the manifolds .. :confused:

I don't know, just what I've heard. Matt chewed on me about it one time. lol