Fuel Gauge Oddity? (and MPG question)

[sprainedmind]

Is it normal to get twice as many miles out of the first half of the tank on the gauge (from full to half full) as the second half (from half full to empty)? It's a 2003 2.5i SE if that makes any difference.

Also, on mainly motorway runs I'm getting about 30MPG on the computer and 320miles on a tank - does that sound about right?

TIA

 

[gannet]

not sure it's twice as many, but yeah mine does tend to go through the second half quicker than the first :?

Ive never got 320 out of a tank, I must have a heavy right foot

 

[nicko]

my gauge seems to be consistent from top half to bottom half (or I haven't really noticed properly)
I think previous BMWs I've had have been too.

Not like the Renault, Subaru and Alfa I've had, which all got much more miles out of the top half than the bottom half

 

[IK.]

I'm fairly sure that is common of MOST cars, if not all. The second half always goes down faster.

 

[Taz]

my last fill up i got 348 miles, must of been very empty

 

[jan_tekin]

That's normal for the tank to drop quicker in the second half. You most probably driving to fast, can manage 400 miles on a tank driving around 60/70.

 

[Blue]

I think it's because the first few miles driven make no difference to the gauge at all, normally because most people fill the tank above the level that the gauge will go up to and therefore it takes a little while for it to drop down again.

In some of my past cars it could be up to 30 miles or more before the needle would move, then despite it being an analogue needle, it actually goes down in increments rather than a smooth flow, so for doing an extra 5 miles you could lose almost an eighth of a tank.

Likewise, I'm not sure that the tank is consistent in shape, i.e. the upper part seems to hold more fuel than the lower part (think of a wine bottle upside down, the neck won't hold as much as the thicker part of the bottle), therefore as you start to move into the thinner parts of the tank the gauge naturally drops more quickly.

 

[johnnyboy_10138]

when i was doing all my road trips this summer, I would only be able to 300 miles before the gas light would come one. So i always filled up at the first station I saw, then I realized i had a quarter tank left. I think once you get the gauge to the F mark it is closely to a being accurate, nothing too drastic.

 

[RichardG]

filled mine up last and the OBC showed 477 miles to empty.

Drove like an angel at a cruise controlled 55mph to Teeside Airport very early on Monday morning and still beat the Sat Nav eta, just shows what can be done when you a clear run, anyway OBC average consumption 41.8mpg.

But yes I have noticed in most cars that bottom half of the tank always to run out faster than first half.

 

[EdButler]

I get 325-380 Miles per tank usually (mostly 350). The Half-Way point is accurate at around 175Miles.

The Z4 has the most accurate fuel gauge i've ever known. My most economical tank was ~415 miles with 17" Wheels on and the fuel gauge went down exactly 50 miles every notch on the gauge! The last 15 miles was going under the last notch

 

[AlanJ]

Likewise, I'm not sure that the tank is consistent in shape, i.e. the upper part seems to hold more fuel than the lower part (think of a wine bottle upside down, the neck won't hold as much as the thicker part of the bottle), therefore as you start to move into the thinner parts of the tank the gauge naturally drops more quickly.

Absolutely.......the way in which the fuel gauge moves depends to some extent of the tank structure. The Zed tank is a saddle type therefore the top larger section will comparatively drain at a slower rate than the two saddles in terms of levels. So there will be a variation in movement depending on what level is in the tank. I use the gauge only as an indicator and generally use the ‘trip’ as a more accurate guide. I try not to let the tank get too empty to avoid the inevitable sludge that accumulates at the bottom.

http://bmwfans.info/parts/catalog/E85/Roadster/Europe/Z4_2.5i-N52/RHD/N/2005/august/browse/fuel_supply/fuel_tank_mounting_parts/

 

[sprainedmind]

Yeah, I'm used to the 2nd half going down faster, but not to this extent. I got exactly 200 miles out of the 1st half and 120 out of the 2nd, with a range reading of 15 miles when I filled it. (I too would like to avoid the worst of the sludge)

If you take those readings as accurate then I went 50% further on one half tank than the other, which seems excessive...