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Discussion Starter #1
Never seen this before on another XF - today the remaining fuel graph in the centre display was exactly one quarter. A while later (after some very gentle cruising due to slow traffic) it had increased and was noticeably above one quarter. What's the deal with that?

Does it somehow adapt the display of the remaining fuel to the driving style/consumption? I expect it to show the absolute amount of fuel in the tank, but this makes me wonder...
 

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Mine's a pre facelift so it doesn't have a graph. But the Kilometers remaining increases quite regularly. Start a full tank with a spirited drive, and then next drive go for a gentle cruise and the Kilometers left often stays the same or even decreases.
Perhaps the graph uses the same calculations?
 

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When you say fuel remaining are you referring to quantity in the tank or the range? The quantity should be absolute - full, half etc. The range does vary depending on the amount of fuel used in the previous 10 miles (I think).

So if you have done some spirited driving then the range will be less than a sedate driving.
 

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If you drive heavy more fuel is pumped in to the pump and the lines... it goes in at a higher pressure... if it doesn't get used it goes down the tank return lines and back to the tank... possibly why it went up?
 

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Could the car have been parked on any kind of incline at some point during these observations?
 

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Discussion Starter #6
I don't mean the range km/miles number but simply the horizontal fuel bar displayed at the bottom of the centre display which I believe all XFs have. First it showed exactly one quarter, then more.

It wasn't parked on an incline but was driven uphill at the beginning of the drive. Perhaps that fools the car to think that there's less fuel in the tank for a while?
 

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I have this phenomenon too (X760) - I think it is some kind of 'on the fly' calculation lol
 

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The range figure is an "on the fly" figure, the tank contents readout shouldn't be, but they can be "confused" by gradients in my experience.
 

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the float is at the front of the tank?
 

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Discussion Starter #10
Ok, seems like parking/driving on an incline is the explanation then. :)
 

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When younger I fitted a right hand tank to my (real) Mini Cooper. The float was on the LH tank and there was a balancing pipe between both tanks.

When I filled up I always filled the RH tank second and put more in than the LH tank. Then for the next 10 miles the fuel gauge would increase as the tanks balanced.

On the occasions when I more in the LH the gauge dropped quicker and being an impoverished student I'd feel even poorer as the car appeared to drink fuel.

All this rambling has absolutely no bearing on Tom's problem. It just his post sparked memories.
 

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Never seen this before on another XF - today the remaining fuel graph in the centre display was exactly one quarter. A while later (after some very gentle cruising due to slow traffic) it had increased and was noticeably above one quarter. What's the deal with that?

Does it somehow adapt the display of the remaining fuel to the driving style/consumption? I expect it to show the absolute amount of fuel in the tank, but this makes me wonder...
Yeah mine does this. I think there's some algo based on driving style. Usually it "fills up" a bit after slowing from faster traffic to slower town driving. It doesn't move by much, but it I'm sure it does.


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Discussion Starter #13
Yeah mine does this. I think there's some algo based on driving style. Usually it "fills up" a bit after slowing from faster traffic to slower town driving. It doesn't move by much, but it I'm sure it does.
Never noticed this on my pre facelift XFS so maybe it's another facelift "feature". :) Good to know that it happens to others too then.
 

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Yeah mine does this. I think there's some algo based on driving style. Usually it "fills up" a bit after slowing from faster traffic to slower town driving. It doesn't move by much, but it I'm sure it does.
I certainly subscribe to this, more than a float level.............at least for mine.........

Invariably, when I start the car I have 'a level', then as I proceed on my journey(usually motorway) the level noticeably increases on the graphical display, with vice-versa for coming off Mway to town driving
 

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Discussion Starter #15
So it seems like the bar is just a graphical version of the calculated range mileage, and not an absolute fuel level readout.
 

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Not as I understand it, it is connected to the sender in the tank.

There was a batch of faulty fuel tank senders a few years back that were giving spurious readings IIRC.
 

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So it seems like the bar is just a graphical version of the calculated range mileage, and not an absolute fuel level readout.
That's certainly more like how it works. The fuel sender does send it's level back to the ECU but it's the range which is used for the graphical bar display under the clock on the centre console.

This is further proven by the fact that the fuel low warning will come up at the same number of miles of range every time. On mine it's absurdly low, something like 38 miles of range left when the warning comes on. The 2.2 diesel I imagine will be more like 70-80 miles left.
 

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Could be related to fluctuating battery voltage with the strange charging system the XF seems to have. Lets the battery discharge then charges it up again or something like that.
 

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Tank design can be quite complex and the fluid in the tank not necessarily level itself all the time. Someone already pointed out that XF could have 'saddle' design. So the level indicators can send signal(s) and the total level is calculated. Graph can then be kind of off-sync for few moments if driven or parked on not even surface. This is confusing but not a big flaw. If you're presice and watch the graph closely this can be an annoying thing. It's harder to notice with classic needle meters.
 
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