In the summer at about 60mph, I got close to 22-24mpg, now it's closer to winter and I'm only getting 18 or 19, I thought engines got better gas mileage if the air going into them was colder? I have the stock air box and my filter looks out of the box clean. Any ideas about what could be causing this?

I have been using the same gas all year, Shell.

 

Well, first the temp changes making it longer to warm the engine, second gas blends chage further aggrevating the problem, and lastly the amount of ethanol in the gas can change from tankful to tankful, which also causes mpg change.

 

Man I'd be jumping for joy if my rig got 18-19 haha

 

No Kidding !!!

 

Gas mileage goes down in the winter because of the colder air. Cooler intake temps will give better power because of the denser air, but it also requires more fuel to maintain the same ratio.

 

Fall and winter gas blends have a higher ethanol content then the summer blends. Ethanol content reduces mpg by as much at 10% and reduces the octane level . I suggest adding Stabil Ethanol gas treatment to your tank.

 

It's not only the winter/ fall/ summer etc blend the ethanol mix ratio is very inconsistent. I have seen %50 ethanol content coem from a E10 pump, average that gives a big problem is %30 and I see it a lot.

 

I too have noticed a drop in my normal 23mpg.. down to 20 now that it has cooled off. I use non-ethanol gas and am now getting the same MPG I was on E10. I am going to run some fuel injector cleaner through mine though and maybe some SeaFoam. Been awhile since it has had a good cleaning.

 

Bingo.
My Jeep doesn't vary much like that but my Taurus SHO will, it drops 10MPG from Summer to winter.

One thing you can be sure of you've got a nearly perfect tune on the engine.
Not many owners have that issue.

 

Most XJs with the 4.0 engine will be in the 16-21 mpg range, give or take a bit depending on efficiency, weather and how hard you are on the skinny pedal.

 

This makes perfect sense, thanks, good to know.

And would anyone know what the limit is on speed/mpg? Like at 70 I get 17mpg, but at 60 I get 20-25? Also, how far can you drive after your low fuel light comes on? (How much gas is left in the tank?)

 

You might be seeing aerodynamics at work. The Cherokee is about as slippery as a brick when it comes to aerodynamics. I don't think it's unusual to see fuel economy suffer with higher speed.

The other day, I took a 300 mile highway ride and kept the speed down around 65 and got over 20 mpg, which I was very happy with. My normal fuel mileage is closer to 17-18.

Sorry, I can't help with the low fuel light question. I normally don't run mine low enough to set the light. I'm not sure if it's true with XJ's, but years ago I was told that it's better to keep plently of fuel in the tank to keep the fuel pump cooler and increase the pump life. I usually fill up at 1/4 tank or more.

 

I'll do some research on the fuel pump thing. Last time I filled up I put in 17.38 gallons and my fuel gauge was showing just over E before I added to it.

 

I would be really happy if my 2000 got 22-24 mpg, I have only checked mine once and I got 17mpg, I don't let mine get to e either, I know on most vehicles that have the pump in the tank that the fuel is suppose to help cool the pump.