Ford fiesta Mk6 - Fuel gage goes down

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Mon 8 Mar 2021 10:59
Ford fiesta Mk6 - Fuel gage goes down - Midge8290

I have a 2007 1.4 16v zetec, everytime I fill her up until she cuts off at the pump and drive her home she says completely full. The next day she is half a gallon gone already. What is it doing that? I can't tell how many mpg if I can't tell how much I'm putting in

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Mon 8 Mar 2021 15:54
Ford fiesta Mk6 - Fuel gage goes down - galileo

Your gauge will not be accurate to better than + or - 1/2 gallon, do not rely on a fuel gaiuge to find your mpg.

If you recorded the mileage when you filled up, read the mileage and number of litres to fill again: divide mileage travelled by litres to fill and multiply the result by 4.55 to find mpg.

This assumes your odometer records miles accurately, most over-read by up to 10%., so worth checking if you can find a measured mile or use SatNav on a straight road.

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Mon 8 Mar 2021 16:23
Ford fiesta Mk6 - Fuel gage goes down - Midge8290

Ok well when I filled up before I put in 15.5 litres and drove 135miles until I filled up with another 18litres. When I filled up with 15.5 litres the needle was just on half mark, the 18litres was just below the half mark but still on the mark it self. Both times the fuel gage read full then dropped down half a gallon the next next

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Mon 8 Mar 2021 19:08
Ford fiesta Mk6 - Fuel gage goes down - galileo

Ok well when I filled up before I put in 15.5 litres and drove 135miles until I filled up with another 18litres. When I filled up with 15.5 litres the needle was just on half mark, the 18litres was just below the half mark but still on the mark it self. Both times the fuel gage read full then dropped down half a gallon the next next

Ok well when I filled up before I put in 15.5 litres and drove 135miles until I filled up with another 18litres. When I filled up with 15.5 litres the needle was just on half mark, the 18litres was just below the half mark but still on the mark it self. Both times the fuel gage read full then dropped down half a gallon the next next

As I explained, it is no use measuring consumption from "half way mark" on the gauge.

The only accurate measure is from pump click-off at full to the next pump click-off at full. (Ideally at the same pump).

If you used exactly 18 litres after driving 135 miles, this equates to 34.125 mpg. Your fuel tank is 45 litres in total, I think.

Fuel gauge movement is not a linear response to fuel level, you are misled if you think you can read a difference of half a gallon, IF the gauge movement was linear this would be 1/20th of the range from E to F, a very small difference and within the margin of error of the gauge.

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Mon 8 Mar 2021 16:27
Ford fiesta Mk6 - Fuel gage goes down - skidpan

This assumes your odometer records miles accurately, most over-read by up to 10%., so worth checking if you can find a measured mile or use SatNav on a straight road.

Most of our cars have had an over reading odometer when checked against a Garmin but never by as much as 10%, its probably been nearer 5% but it still makes the car more economical then it seems. The Ford odometers were spot on. The odometer in the Kia Ceed was the odd man out, it read about 5% under.

I will be checking ours in the iV shortly. The previous Superb under read as well but by an insignificant 0.2%

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Tue 9 Mar 2021 18:48
Ford fiesta Mk6 - Fuel gage goes down - focussed

I have a 2007 1.4 16v zetec, everytime I fill her up until she cuts off at the pump and drive her home she says completely full. The next day she is half a gallon gone already. What is it doing that? I can't tell how many mpg if I can't tell how much I'm putting in

Plastic fuel tanks can be a little flexible, you load the tank by filling it up. Overnight the tank flexes a little and there's your half a gallon gone. It's not going to take much flex to make half a gallon.

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Tue 9 Mar 2021 19:10
Ford fiesta Mk6 - Fuel gage goes down - Xileno

That's interesting, thanks. I hadn't ever thought about that. It might explain why my Renault Megane fuel gauge used to behave like that, seeing as it had a plastic tank.

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Tue 9 Mar 2021 20:19
Ford fiesta Mk6 - Fuel gage goes down - jc2
No tank can be filled completely full-they are designed so that a small amount of air is trapped to cope with expansion due to temperature changes-these can be caused by changes in ambient temp.,differences in temp.from storage tank to vehicle tank or just running engine-virtually all modern vehicles(last 40yrs.)have recirculatory fuel systems-this heats the fuel.
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Tue 9 Mar 2021 21:08
Ford fiesta Mk6 - Fuel gage goes down - blindspot

is the car parked on the level., when you filled

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Tue 9 Mar 2021 23:26
Ford fiesta Mk6 - Fuel gage goes down - Andrew-T
No tank can be filled completely full-they are designed so that a small amount of air is trapped to cope with expansion due to temperature changes-

I have always avoided filling a tank to the cut-off for just this reason. Plus the unnecessary extra weight in the car. Most 21st-century cars show you instantaneous and overall consumption figures, which may or may not be optimistic.

I prefer to buy fuel 18.2 litres at a time (= 4 gallons) - more if you prefer. After 5 of those you should get a good estimate of consumption. Then all you need do is check your odometer against M-way Km markers or your satnav. If your odometer over-reads, your consumption will be equally optimistic.

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Wed 10 Mar 2021 09:33
Ford fiesta Mk6 - Fuel gage goes down - focussed

Car fuel tanks are mostly plastic nowadays. They are also now fitted under the rear or centre floor since being moved from the rear of the car for safety in a collision.

So by necessity they are pretty much flat in profile.

A rough and dirty calculation. Assume the fuel tank is approx 75 x 50 cm to account for half a gallon by the tank bottom flexing, it only has to sag by about 0.6 to 0.7 cm from the weight of the fuel, that's 6 to 7 mm which sounds reasonable.

Edited by focussed on 10/03/2021 at 09:34

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