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Discussion Starter · #1 ·
Hi all, this is likely to be the first of many questions. When test driving my TF I noticed the fuel gauge was on almost the red, despite the technician having just put a jerry can full into the tank. I had to stop mid-test-drive and stick a tenner in just to be safe :LOL:

It was only after stopping to fill the tank on my way home that I noticed something odd - the fuel gauge initially was reading exactly the same as it had been before I filled up. I then watched it slowly rise to just above the max mark on the gauge over the course of the next few minutes driving.

Is this normal? I would have thought the sender was just a typical float so surely it would update immediately? Is there some sort of delay on it to stop the needle bouncing up and down if the fuel is sloshing about maybe?
 

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If you cut the power to the cluster, fuel gauge will stop rising, and resume rising when you return power to the cluster. And yes, the rise is slow.
 

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2002 MG TF 135 VE51FTF
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As a new owner you will also note the gauge will still indicate the level with the ignition off this is normal the gauge remains at the level recorded prior to power off. When I first got mine I thought the gauge must be permanently live but this is not the case, I've since discovered this is common on Rover's of this period.
 

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Discussion Starter · #6 ·
The F/TF鈥檚 fuel gauge is not linear but logarithmic, as a result the gauge is much more accurate between empty and half full (where it is more important).
That makes sense, it seemed to hover around the full line for about 50 miles or so before it started dropping off, decreasing more quickly as the level became lower
 

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'06 ZR +120 (HQM) '04 ZR 105 (IAB)
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It has quite a lot to do with the way the float for the in tank sensor is situated and the geometry of its fall from full to empty - the float arm pivots from near the lower end of the fuel pump intake (ie. near the bottom of the tank), so as the fuel level falls from the point of a full tank, the float/arm is at the top of the curve, so the fuel has to fall some distance to make a small change to the gauge indicator needle. As the fuel level drops down towards a half full tank, the direction of travel of the float is more directly downwards and so it has a gradually greater effect on the gauge as the tank empties,
 

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It has quite a lot to do with the way the float for the in tank sensor is situated and the geometry of its fall from full to empty - the float arm pivots from near the lower end of the fuel pump intake (ie. near the bottom of the tank), so as the fuel level falls from the point of a full tank, the float/arm is at the top of the curve, so the fuel has to fall some distance to make a small change to the gauge indicator needle. As the fuel level drops down towards a half full tank, the direction of travel of the float is more directly downwards and so it has a gradually greater effect on the gauge as the tank empties,
Interesting information: Just out of interest, as the fuel tank has an unusual shape, (see below)
Hood Automotive tire Motor vehicle Automotive exterior Bumper


Does this shape mean that after (for instance) a long trip cruising on a motorway, starting with a half-full tank, you are likely to have a "dead" volume of fuel in the area circled in red. I am ASSUMING (a dangerous practice, I know!) that fuel is ONLY sucked from the side directly below the fuel pump access hole (circled in green). If I am correct, does that then mean that hard cornering to the right, or parking across a steep slope tilting the car to the left, would move that "dead" fuel over to the side which gets pumped?? If this is the case, it could be a useful technique for accessing and (then) pumping out old, stale fuel for an F or TF which has been parked-up for several years?
 

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97 BRG MGF. 2009 SKODA SUPERB.
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Interesting information: Just out of interest, as the fuel tank has an unusual shape, (see below)
View attachment 139552

Does this shape mean that after (for instance) a long trip cruising on a motorway, starting with a half-full tank, you are likely to have a "dead" volume of fuel in the area circled in red. I am ASSUMING (a dangerous practice, I know!) that fuel is ONLY sucked from the side directly below the fuel pump access hole (circled in green). If I am correct, does that then mean that hard cornering to the right, or parking across a steep slope tilting the car to the left, would move that "dead" fuel over to the side which gets pumped?? If this is the case, it could be a useful technique for accessing and (then) pumping out old, stale fuel for an F or TF which has been parked-up for several years?
I have often had the same thought about the shape of the tank, I either read about it somewhere or it was raised in this Forum before. Regards. D4KGP.
 

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'06 ZR +120 (HQM) '04 ZR 105 (IAB)
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.....as the fuel tank has an unusual shape, ......Does this shape mean that after (for instance) a long trip cruising on a motorway, starting with a half-full tank, you are likely to have a "dead" volume of fuel in the area circled in red.
I have to admit that I hadn't realised that the F/TF tank was quite such a peculiar shape, so I don't really know the answer, but (unless there is some kind of linking pipework between the two low points), I would think that it is perfectly possible. I woud think normal cornering may well lead to a good deal of the fuel from the offside low point spilling up the slope into the nearside where the pump is, which may well be the reason for that side of the tank having a flat inclined side, rather than being moulded to fit down into the gap next to the tunnel.
 

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If I am correct, does that then mean that hard cornering to the right would move that "dead" fuel over to the side which gets pumped?
Yes, a hard right turn or cornering will move fuel from right side of the tank to the fuel pick up on the left side, you will notice the fuel gauge needle rise from say, an 1/8 of a tank to a 1/4 tank.
 
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