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Almost ran out of gas today

15K views 49 replies 37 participants last post by  underscore 
#1 ·
I left the house in a rush for an appointment and saw that my computer indicated I had about 20 miles left of gas. The street that I wanted to take was closed off, so I took an on ramp and got on the freeway, thinking I would take the nearest exit. Well, as luck would have it, that was blocked off, so I exited at the next offramp, several miles away. By the time I got off, I had 7 miles left, which was probably an accurate distance reading, since I was now at least 12-13 miles from my home.

I searched for a gas station and it went down to 0 miles, while I waited at a long stoplight, and then back up to 2 miles. Kind of scary, but car wasn't shaking yet. And thankfully the signal light eventually changed, and I was able to get a full tank. Interestingly enough, the idiot gas light didn't turn on until I had about 10 miles left according to the computer.

I put in about 17.75 gallons.

Do you think the computer is pessimistic? How many gallons are supposed to be left when the idiot light goes on?
 
#3 ·
Probably around 2-3 gallons left in the gas tank. I have driven around 15-20 miles after the computer showed 0 miles.
 
#6 ·
On my Liberty, I recall reading that the computer estimates over the last several tanks by the mpg. Plus I think they just gave us extra room so you don’t run it empty. When my fuel light comes on, I still have three gallons left.
 
#7 ·
Thanks Everyone for the quick responses, this is all very helpful.

That was kind of scary, but I feel much better now. I need all the extra miles I can get, since it seems like I am filling it up all the time.

I wish our tank was a couple gallons larger. Well, I guess since I haven't been using my last couple gallons, this information might be a big help as I put it to use.
 
#9 ·
For your info, it's not a good idea to run lower than 1/4 tank. Your fuel pump is located in the tank and uses the fuel to cool and lubricate the pump. If you run less than 1/4 the cooling capacity of the gas is not nearly what it was when full and your pump will run warmer. If you run like this often you will probably become a victim of a fuel pump failure after your factory warranty expires. (Pumps like this know when it's done and they wait until 100 miles after the warranty expires before quitting.)

My ZJ's fuel tank wasn't allowed to dip below 1/4 during it's life and it went to 180K miles before it bit the dust.

Yet, my 99 WJ went too low once (thanks to the wife) and it quit around 45K.

I know it stinks to have to fill up more often, but fuel pumps cost almost $550 just for the pump, and it's usually another $200 in labor to change. Save yourself some money and fill it up more often.

Also, when filling up, try to top it off. The filter in the fuel tank is cleaned when you fill it up. The debris reside in the bottom of the tank where they stay until you pull the fuel pump someday. They will not hurt anything there. If you don't clean the filter by filling up the pump will have to work harder to get the required fuel pressure and eventually it will result in premature failure of the pump as well.

BTW, if a pump lives to 150K, it has surpassed it's life expectancy.

Just trying to pass a little info.
 
#39 ·
For your info, it's not a good idea to run lower than 1/4 tank. Your fuel pump is located in the tank and uses the fuel to cool and lubricate the pump. If you run less than 1/4 the cooling capacity of the gas is not nearly what it was when full and your pump will run warmer. If you run like this often you will probably become a victim of a fuel pump failure after your factory warranty expires. (Pumps like this know when it's done and they wait until 100 miles after the warranty expires before quitting.)

My ZJ's fuel tank wasn't allowed to dip below 1/4 during it's life and it went to 180K miles before it bit the dust.

Yet, my 99 WJ went too low once (thanks to the wife) and it quit around 45K.

I know it stinks to have to fill up more often, but fuel pumps cost almost $550 just for the pump, and it's usually another $200 in labor to change. Save yourself some money and fill it up more often.

Also, when filling up, try to top it off. The filter in the fuel tank is cleaned when you fill it up. The debris reside in the bottom of the tank where they stay until you pull the fuel pump someday. They will not hurt anything there. If you don't clean the filter by filling up the pump will have to work harder to get the required fuel pressure and eventually it will result in premature failure of the pump as well.

BTW, if a pump lives to 150K, it has surpassed it's life expectancy.

Just trying to pass a little info.
Agreed that is definitely causes problems to run out of gas in a modern car. At a minimum you'd want to go ahead and change out any and all fuel filters, but it still might shorten the life of components.

The only thing I'll add is that "topping off" is probably fine in ZJs, particularly the older ones, but you generally should not do that in newer cars with all the extra evaporative emissions equipment. You can end up with liquid where vapor belongs and it can muck up some of that stuff, mainly the charcoal canister I'm guessing.
 
#11 ·
Airmanwoody said:
Also, when filling up, try to top it off. The filter in the fuel tank is cleaned when you fill it up. The debris reside in the bottom of the tank where they stay until you pull the fuel pump someday. They will not hurt anything there. If you don't clean the filter by filling up the pump will have to work harder to get the required fuel pressure and eventually it will result in premature failure of the pump as well.
Bad for the enviroment to fill up the filler neck past where it clicks...
 
#12 ·
When the gas light comes the computer is going to tell you that your have 0 gallons left but you will have 2-3 gallons left when the light comes. I know in my wrangler I had 3 gallons left when the gas light came on.
 
#13 ·
Thanks for all the advice! I think I am going to aim for filling up when the light goes on. Today, shortly after the light went on, it again showed 0 miles left, and I put in just under 18 gallons. So, I probably have a couple gallons left, and my fuel pump should be okay. Since the tank is so small, I don't think I'm willing to keep filling it up every 3/4 tank.
 
#14 ·
I ran the tank down this week just for the heck of it.
When I had the low fuel light come on, the EVIC showed I had 8 miles left til empty.
I drove around for 30 miles more with the light on. The evic kept displaying between 2, 5, and 8 miles til empty the entire time.
When I finally decided to pull over and fuel up, I was only able to pump 18 gallons into the tank.
At least I know I have a little safety cushion should I ever need to push the limit.
 
#15 ·
It's a pretty bad idea to drive around with less than 1/2 tank in the winter, atleast if you live where it snows. If you ever get caught in anything, i'm sure you'd rather have a nearly full tank of gas instead of having only 1/8th of a tank becuase you like to wait until the last minute to fill up.
 
#19 ·
I try to fill up when the tank is half empty since it's nice to be prepared as the Boy Scouts say. I did let it run down last week and the EVIC showed 40 miles left when the warning light came on.

I then drove about 30 miles before putting 18.37 gallons of fuel in the tank. Divide that into 368 miles on the odometer and it is 20.1 MPG while the EVIC said the average mileage was 18.5.
 
#21 ·
I try to fill up when the tank is half empty since it's nice to be prepared as the Boy Scouts say. I did let it run down last week and the EVIC showed 40 miles left when the warning light came on.

I then drove about 30 miles before putting 18.37 gallons of fuel in the tank. Divide that into 368 miles on the odometer and it is 20.1 MPG while the EVIC said the average mileage was 18.5.
DUDE, you got 368 on ONE tank of gas?!? wow, I usually pull 240-260.
 
#20 ·
The fuel pump does not draw directly from the bottom of the fuel tank. It is located inside the module reservior (bucket) and has a sock filter on the inlet that is designed to filter out particles that are large enough to damage the pump impeller elements. The pump is designed to operate all the way down to no fuel left in the tank without an issue.

While the fuel surrounding the pump certainly does provide a certain level of heat rejection, it's unlikely that the pump will overheat to the point that it is permenantly damaged because the engine will stall almost immediately when the fuel is gone. At that point the pump will be shutoff by the vehicles electronics and won't spin dry.

Woody - I'm not sure what you mean by your comments that the filter is cleaned by topping off the fuel tank. There are two filters in the WK/XK fuel pump module and neither one is affected in such a manner. Both are designed for life-of-vehicle performance and there is no active or passive system that flushes them clean. The fuel pump does not pull fuel in from the tank either - it draws fuel in from the module reservoir, which is filled via a passive device known as a jet or venturi pump. The pump itself is designed and tested to operate with highly contaminated fuel ... significantly more contaminated than you are ever likely to find in developed parts of the world.
 
#22 ·
agree with CanadianJP.

Also, I don't know if it's the case with WKs or not, but oftentimes there will always be 1 gallon or so that can't be used. It sits in the very bottom of the tank where the sediment is allowed to collect. So that 20 gallon tank may have 2 gallons in it, but only 1 usable. The only way to truly know where "E" is, is to run out of gas. Some cars handle this fine. Some can be a bugger (older GM) to restart from an empty tank.

The '11s have larger 24 gallon tanks! I wonder if a swap is possible without cutting/drilling/fabricating? I drive gently and still fill up every 280 miles... My ZJ would go 400miles per tank.

M

M
 
#23 ·
The WK tank, like most Chrysler fuel tanks, has a sump or depression that the fuel pump module sits in - not very deep (1/4") but it's enough. As such you can actually suck the fuel tank essentially dry, assuming you are just cruising down the highway. In that case there won't be more than a few hundred milli-liters of fuel left. However if you are going to try that you'll need to have a gallon or two in a can because once you run out your done!

The current WK's low fuel warning light turns on early because the level sensor has very poor resolution down low in the tank. As such it has difficulty measuring the fuel level really accurately. That results in a low fuel warning strategy that is very conservative, to ensure you don't run out of fuel while driving, regardless of if you are towing a trailer or just running around town.

The 2011 WK tank will not swap into the previous generation WK. The vehicle underbody is totally different, plus 2011 WK has an independent rear suspension. The new underbody and suspension allow a much larger saddle tank to be packaged in the vehicle. The solid axle in the first generation WK did not allow for a saddle tank to be packaged because the prop shaft has a large articulation envelope.
 
#24 ·
Hey CanadianJP.... much respect, dude. Great info.

Subaru used those saddle tanks and actually had dual level sensors to make sure they got it right. The fuel return would fire through a bernoulli tube to "suck" the secondary side dry, feeding the primary. It was a complicated system for a tank but worked without fail. Wonder if DCX (or whoever they are now) is doing similar.

M
 
#25 ·
Just an FYI, wkjeeps.com list the 05-10 tank as 21 gallons. Your fuel light comes on with about 4 gal left in the "reserve". This reserve is used to cool the fuel pump. I am not a mechanic or claim to be one, but my guess: if you are on the freeway and driving and the light comes on, you don't have to panic. I have pushed my wk for about 30-35 miles past to get to the exit I wanted. My wk still rides like it always did.

And as for the filling all the way up not being "Green". Most on here have lifted Jeeps, with 4.7 or higer engines. Last I checked this isn't a mini cooper site
 
#26 ·
Meep - you are right about saddle tanks. Almost universally they use two level sensors - one on each side and then have some crazy, complicated software algorithm to filter and process the signals to get a stable, useful signal on the gauge. And yes, there is only one electric fuel pump in most (but not all) saddle tanks. A small amount of either the supply fuel (returnless systems) or return fuel (return systems) is used to drive a jet pump (or you can call it a venturi pump or bernoulli tube) to transfer the fuel from the sub-side to the main-side. In fact, every modern fuel injected vehicle that has a fuel pump module (as opposed to a pump-on-a-stick) has a jet pump to bring fuel from the tank into the reservoir bucket. A saddle tank has a second jet pump to transfer the fuel from the sub-side to the bucket. Jet pumps are almost fool-proof, since they are based on simple fluid dynamics and have no moving parts. As long as the orifice doesn't plug with junk they will run flawlessly, and most have a screen to prevent large garbage from entering them and plugging them up.

I keep reading comments that there is a low fuel strategy to keep the fuel pump cool. That isn't the case. The low fuel warning system is there to prevent the driver from running out of fuel without sufficient warning.

The fuel pump on modern cars is located inside the reservoir bucket and the reservoir bucket is always full, because the jet pump in the reservoir constantly transfers fuel from the tank into the bucket. The jet is sized to ensure the bucket stays full even when the engine is running at WOT and consuming the maximum fuel. The only time the bucket level drops is when the fuel in the tank is low and sloshes away from the jet pump. When the fuel sloshes back to the jet pickup the jet action restarts and fuel is again transferd back into the bucket. There can be 10mm of fuel in the tank and the bucket will be full and overflowing back into the tank. As such the pump is always submerged in fuel, right up until the point that the tank is dry and the pump sends the last of the fuel to the engine. Then the pump is no longer submerged, but by then the engine is about to stall so it really doesn't matter. Back in the day, before reservoir type modules, things were different, but the number of vehicles using reservoirless modules is incredibly small and hasn't included a Jeep in over 10 years. All TJ, KJ, WJ, WK, XK and a lot of XJ's use reservoir modules.
 
#27 ·
C'JP.. Love it.... dang good info.

I dismantled a cpl failed fuel pumps years ago when MPFI was still a new thing and found that the motor/pump unit, all in one cylinder, was 100% submersed in fuel internally, including the motor armature, brushes, commutator. The armature was set in resin to be rotationally smooth. So...going even further, if similar designs are used in our pumps, *any* fuel that flows will cool the pump, regardless of what is surrounding the casing.

Your explanation of the cartridge makes a lot of sense. Great design idea, frankly, and explains why newer vehicles don't stutter stutter run, stutter, die.... they just quit w/o warning. Neat design! Thank you for taking the time to describe!

M
 
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