Hello, all, hoping you can help me.

I've been having an issue with my gas gauge on my 07 XKR and need your help to confirm or disagree with what my dealer has told me.

My gas gauge appears to think my car only has a 12 gallon tank vs. the 18.8 w/1.6 gallon reserve per the manual. It reads 1/4 tank after about 3 gallons, 1/2 tank after about 6 gallons. I don't believe this is normal. The dealer's explanation is this isn't abnormal, didn't find fault codes, and found all resistance within spec...but they didn't drain the tank or move the float...just took the readings at the level it was at, 1/4 tank.

They claim this is working as designed.

How do your gas gauges work, anyone else with this issue, or do you see 1/4 tank after 4.3 gallons, 1/2 tank after 8.6, etc? Any suggestions on what to do next? My warranty is up within about 1 year, so I want to make sure to take care of everything wrong.

Please let me know.

Thanks.

Christian

 

Whenever I fill mine I can only get the indicator (red bar) to 7/8 full.

After some research I found the breather valve on gas tanks sometimes gets clogged by mud or insect nests. Next time I have mine on a lift I'm going to try to find the breather valve on the tank and check it as this is the only explanation I could find.

 

Thanks, Mike, I find its 7/8ths if I don't top up....or sometimes it takes a little while to register that last eighth.

Everyone else, do you find your gas gauge to generally be accurate? Do you fill up somewhere near 9 gallons after it reads 1/2 for example?

Any feedback would help as if mostly these work normally, mine's not right.

Thanks again.

Christian

 

Do you find that often, with some gas pumps, that the automatic shutoff kicks in before the tank is full? My X350 XJ sedan had this issue. What happens is the vent line from the gas tanks to the charcoal canister can clog and prevent vapors from leaving the fuel tank. This means that when fuel comes into the system during refueling. the air that is being displaced has nowhere to go. Therefore, you may not be filling the tank all the way. Coincidentally, filling up the tank too high is a sure fire way to cause liquid fuel to make its way into the vent line and to the charcoal canister and gum up the whole system.

 

By the way, how are you determining that after you put 4.3 gallons in it reads 1/4? Are you deducing it from when the gas pump shuts off?

 

I'm seeing that after filling the tank up (pump shuts off, usually top off once more till it shuts off again, gauge reads full) I drive enough to use 3 gallons and it says I've used 1/4 tank....after 2-3 more gallons, 1/2 tank....I fill up and confirm its only used that amount. I'm using a combination of the mpg gauge + miles driven as well as confirming with the amount it takes to fill up again. The mpg gauge is relatively accurate... for example, I recently drove 90 miles and it went from full to 1/2 tank....mixed city/highway driving, about 15.5 mpg per the gauge, tank took a little less than 6 gallons.

My next step is to drive to "empty" on the gauge and then fill up. Per the manual, that should take about 17.2 gallons to fill (18.8 tank less 1.6 reserve at "empty").

I don't have a way to drain the tank completely and test the capacity myself, and the dealer didn't want to do it as my car is "functioning as designed". I need feedback from other similar (07 - 09, perhaps?) XK owners to know if they use up closer to 9 gallons in 1/2 tank.

Thanks.

 

The "range" is another way the car tells you how much fuel you have remaining. Have you compared the "range" to the reading on the gauge?

It's been my experience that fuel gauges often have a personality of their own, and rarely are they completely linear. Some read full for a long time, and then drop off to empty very quickly. Others do the opposite. In the 4 months that I drove my car before putting it away for the winter, I never paid attention to how accurate the reading was during the entire cycle. I just drove it until it was near empty and then filled it up. I just wish it didn't go from full to empty so quickly! The tank is very small.

 

I think you might be worrying about it too much, but I will try to confirm with you how many gallons it takes to fill up--I should be filling it up soon.

If you are measuring primarily from when the gas pump clicks off, and are complaining at the same time that the tank seems to read "empty" too quickly, I think you may have the problem where the tank may not be filling fully, which may indicate a clogged/faulty charcoal canister/vent tube. I don't know exactly how you can test this without running the tank completely dry. Often, fuel tanks read full for quite a long time before they start to show a drop in fuel level.

 

Thank you. If possible, please let me know what your gas gauge level was before the fill and how many gallons it took.

Thanks again.

 

I don't generally use the estimated range as my mileage trends to vary and most cars I've had use some average mileage over a recent set of miles...so it's not very accurate for me. I normally estimate my range myself via current mileage and remaining fuel, which is one reason this issue it's frustrating. I'm fairly sure the tank it's full (I've used a few pumps without vapor recovery sleeves and could hear the tank full after the first auto shutoff or two, and I've topped it off on a few trips....I realize that can be risky for the reasons you've mentioned) and reading properly when full...

Thanks.

 

I don't recall any car I have ever owned having a perfectly linear gas gage. It has never concerned me much as the important thing was how it read at full and the last 1/4 tank. I do recall replacing a number of sender assbys over the years.


Given the expense of aircraft grade instrumentation, where it's really really important, perhaps that's how the auto OEMs feel too.

 

My point was to compare the range against the gas gauge throughout the usage of an entire tank of gas.

 

I agree with you here, I'm not expecting perfectly linear. It drops quickly initially, then hangs around 1/2 for a while...that doesn't bother me. My concern is that is goes to "empty" after roughly 12 gallons used....with an 18.8 gallon tank. I've never had a car with a gauge so far off...especially when the manual tells me to expect empty after about 17 gallons.

How many gallons does your car take at 1/4 tank or empty? It would help with a reference point.

Thank you.

 

Got it, thanks. I'll start looking at the range.

 

Ok, the tank was down to approximately 1/4 and said it had 80 miles of range left. I filled it up with 11.8 gallons or so, and then the range said approximately 300 miles.

What are your readings? I don't understand. Is it 9 gallons to fill up from 1/4 of a tank?

 

Thanks, that's about what I would expect if my gauge was correct. I've seen roughly 9 gallons to fill once I reach 1/4 tank. I'm running it to "empty" on the gauge this tank....next tank I may run it past that point a ways to see if I can confirm the tank holds close to the 18.8 gallons....

 

Just carry a couple gallons of gas in your trunk so you don't get stranded! Hah!

 

Mabe it's just me...........but I have a slighly different view on RANGE. It's my view that you can go fill up the tank and then view the RANGE. Then get on the hwy and drive quite some distance and see RANGE figure has actually gotten larger. That's because when driving using the last tank you might have been doing city driving and now your doing hwy/interstate driving, meaning your now getting better mpg than the city driving and the computer sees this happening and makes adjustment to the RANGE figure.

Take it for what it' worth. Just what I've seen in the past. Make sense? Yes? No?

I'm talking only about the figure seen on RANGE, not the fuel gauge reading. I rarely if ever let my car(s) get below 1/8 - 1/4 as protection for the fuel pump (cooling). To R square a fuel pump you've got to lower the fuel tank on most modern cars.

 

I drove my 87 XK this morning til the gauge showed half way. Unfortunatley I had to drive another approx 15 miles til I found a station. It took 8.95 gallons to fill up to the neck (kept filling til it wouldn't take anymore). The gauge was just to the left of the 1/2 tank hash mark. Mabe about the width of the hash mark ...to the left of the 1/2 tank hash mark. Make sense?

Then drove up north and back til the gauge read 3/4 full. This time the gauge was right on the 3/4 hash mark and it took 4.47 gallons.

I think it's fairly accurate given it's just a automobile gas tank and gauge. My tank is supposed to be 18.7 gallons if memory serves.

Disregard part of my post prior to this one. I was mixing a bit too much what a Chevy I own acts like.

If this were a F-16 I'd say the Jaguar has Blk 15 avionics and the Chevy has Blk 60 avionics, and sad to say the Chevy is a 2000 model and the Jag is 2007. A smidge disappointing on the Jaguar side. Not a big deal though.

EDIT: Talking about the time when I hit the half tank hash mark and had to drive some more to find a gas station...........it seemed to me that the "needle" dropped more than you would expect by the time I found a gas station. I think I drove approx 10- 15 miles to find a station and by that time the "needle" had gone past the half way mark by the width of the hash mark.

 

Thanks, that's helpful information. That's about what I would expect from my gauge.