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Gas Gauge/Low Fuel Light/Range Estimation Question

Badgerdon

Well-known member
Very interesting discussions and I get the rural state concerns and have driven across WY, MT many times. Having owned 5 jeeps (when my 22 GCL arrives soon) and several luxury SUVs (Lexus, BMW, Mercedes) fuel estimates are constantly all over the map. I don’t really find FCA vehicles outside of the wide margin of error that typically is built in to these estimates. I do endorse the 1/4 tank rule just to be safe. I also think that the fuel pump ages faster when consistently being in low fuel situations. I have a BMW 3 series where the fuel pump failed due to this situation.

With regard to mileage estimates and driving situations, I think these are huge factors that contribute to the margin of error. Yes, hills, highway vs. city driving make a difference…sometimes a massive difference. Also, road surface is a factor. Friction robs plenty of power from a vehicle. AWD, FWD, 4WD also has an effect. Yes, that stuff is built in to the stated MPG numbers, but, the variable is driver behavior. With selectable AWD or 4WD, how often that is switched on and off also makes a difference. Lastly, gas octane, ethanol mix, weather (humidity) also has an effect on how efficient the engine is. Clean, intaking dry air is optimal, but not a reality.

I am by no means an engineer, just a car enthusiast. In this case, your mileage may vary (YMMV) is relevant and just a fact of internal combustion life.

I did explore getting a full EV and hybrid before my GCL purchase. Take this thread discussion and multiply it by 1,000. Talk about estimates and accuracy of charging….all over the map. And the map makes a huge difference. Winter in Wisconsin just destroys any rational estimates of a charge, primary reason I chose not to go that direction..



There's an expansion reservoir that isn't really meant to be filled (but you can if you go slow), and I'm guessing that might be 2-3 gallons. Lat time, the auto-stop on the pump allowed 22.5 gallons, which might bring me to 23 gallons, and if the expansion reservoir is 2-3 gallons plus the filler neck (filling slowly to top off), that's how I assume I get to 26 gallons of fuel, meaning the totally full capacity, if you ran it dry, might be 26-27 gallons (with the expansion reservoir and filler neck).

Nevertheless, the gauge is not remotely accurate if I can put 17 gallons in with it showing a bit over half a tank. Even if you subtract 3 gallons for the top off, that's 14 gallons at over half full indicated, which would equate to a 28 or 29 gallon tank instead of 23. That's a pretty big error. How long have we been manufacturing gas gauges now? Sheesh.
 
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Sarge

Well-known member
I usually fill up at 1/4 tank, but my wife will drive it until the light comes on and then leave me to fill it up, so that's how I keep getting to that low level. I'm also concerned though, because none of the 30 cars I've had in the past three decades has had a fuel light not come on until there's only a gallon left, few of them have had gas mileage this low, none of them were remotely this inaccurate at 1/2 tank, and the 'range remaining' was always pretty accurate on cars that had the capability. My BMW's would count all the way down to zero, and still go another mile or so (driving across the desert at night with no filling stations).

So, living in Wyoming, I need to at the very least figure out how many gallons are truly left in this thing when that low fuel light comes on, because that can be pretty serious in the winter in very rural places. It's also a problem that it always says it has nearly fifty miles remaining, and then 'low fuel'. I've never seen a 'remaining range' estimate lower than 48 miles, and it seems like the actual range is more like 10-20 miles. And lets face it, no one looks at the 'range remaining' when you've got 100+ miles left, but people rely on it when they're getting low, running late, etc.

If the dealer can't get an answer from STAR techs, I'm just going to let it run out of gas at the pump one day just so I can figure out what the full topped-off capacity is. The autostop on the pump can vary in terms of how full it actually is due to bubbling of the generally ethanol-included gas, so that point alone is not an accurate measure in my mind. You have to top it off to know.
 

Sarge

Well-known member
Today, at about one or two digital ticks under 1/2, I put in 15.7 gallons when the pump auto stopped, and then topped it off with 19.6 gallons total.

If it's 23 gallons when the pump shuts off, that means I only had 5.3 gallons until the fuel light should come on. 7.3 is not even close to 1/2 of 23, either way.

The dangerous part is still the fact that it says 48 miles remaining and then the fuel light comes on, and then it takes almost 26 gallons to top off, which means I probably barely have a gallon when the fuel light comes on, or 10-15 miles remaining, not 40+ miles. If you're on a long road trip, it's easy to rely on the fuel light, and in Wyoming winters, that can be really, really bad.

IMG_3351.jpgIMG_3352.jpgIMG_3354.jpg
 

GCOverland

Well-known member
BTW, it's the same on mine.

When, the gauge shows I still have half a tank, I can put way more fuel into it than half of its posted capacity.

My first impression was "Wow, I did that many miles with only half a tank of gas?" - NOPE - LOL!
 

Sarge

Well-known member
If you can take some photos and post them, that would be helpful. At some point we need Jeep to see this thread so they can see it's (probably) widespread, and hopefully get a fix. It would seem like maybe a software fix would work, but it would help to see how consistent the problem is (ie filling at half tank, filling from empty, pump auto shutoff vs topping off, etc).

They obviously have a litany of more serious issues to solve, but this needs to get on their list at least.
 

GCOverland

Well-known member
OOOOK.....Just came back from filling her up - LOL!

It happened to be that I also had a half tank of gas left - according to the fuel gauge.

Here are my results:

The first image showing me approaching the gas station. Range is at 195 miles to empty:

Fuel1.jpg

Next, a few moments later, I moved a spot up. Now, my range is at 199 miles:

Fuel2.jpg

...and when I finally reached my spot, I was at 203 miles to empty:

Fuel3.jpg

At the time it "clicked", I was here:

Fuel4.jpg
 

GCOverland

Well-known member
I stopped at 14.742 Gallons but I could have at least squeezed 15 Gallons in - probably more. Due to the fact that there were long lines, I stopped early. But even @ 15 Gallons, the vehicle would have a total tank capacity of 30 Gallons - IF the gauge would be accurate (and it's not).

How do I know? Well, see for yourself what happened. The following images are in the same chronological order as the images above, from 1-3:

195 Miles: Gauge1.jpg
199 Miles: Gauge2.jpg
203 Miles: Gauge3.jpg

So as you can see, it's not "just" the mileage-display that adjusts.

The GAUGE itself also changes. Mt tank got physically fuller just by waiting in line - LOL! That, I have not seen on a vehicle before - certainly not on vehicles with a manual display - LOL!

No surprise this is confusing. I certainly would not have expected that and I don't think this is a good idea.
 

GCOverland

Well-known member
Here's my theory - at least for the V6:

If you reach a range of 200 miles to empty, the fuel gauge will show that your tank is half full although it probably isn't based on your actual driving until you hit that mark.

If you are cruising on the Interstate, you might have significantly less fuel left as you would after driving aggressively or in stop & go.
 

Sarge

Well-known member
Jeez. It makes you wonder if it strictly uses a tank sensor, or if it's calculating off of fuel burn rate. It could be related to the car being off-level, too, of course.

Mine shows 'full' on the gauge before the pump's auto stop even clicks, and then I can put another 3-4 gallons in if I run it real slow. When doing a very slow, trickle-fill top off, you're basically allowing the pressure to slowly force the air to bubble down and out the fuel filler, thereby filling the expansion reservoir.

They don't intend for you to do that (I'm not really sure why it's a bad idea to do that, except in high temps you might be causing the fuel to expand and flow out the overflow (ie sitting in summer desert heat, etc). So that aspect is what it is, but when you're showing 1/2 tank, it should only take roughly 11.5 gallons to fill it. So mine is off by about 4 gallons at that point (i.e. I have only 7 gallons actually remaining at 1/2 indicated).
 
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GCOverland

Well-known member
It might be just me but I would prefer a range-display based on my driving-style BUT.... The GAUGE should ALWAYS reflect the PHYSICAL amount of fuel left in the tank - no matter what.
 

Deere78

Well-known member
Just filled up ours. Showed half tank with 250 miles to E. Filled until it kicked off. Put 13 gallons in it. So it’s off by a little but not as bad as some of you guys are seeing.
 

GCOverland

Well-known member
Just filled up ours. Showed half tank with 250 miles to E. Filled until it kicked off. Put 13 gallons in it. So it’s off by a little but not as bad as some of you guys are seeing.
That sounds pretty accurate. I would not complain if I would be that close on mine - LOL.
 

Sarge

Well-known member
You also have to be aware that gas with ethanol in it foams up and triggers the autostop prematurely. I would say, generally, the most valid way to fill it to the intended capacity is to give it one more slower pump after waiting 15 seconds and activating the pump at a slower rate. After that, if you very slowly put more in, it's probably filling the expansion reservoir.
 
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