Fuel consumption from full tank to empty vs frequent refill.

[guest9814]

Hi everyone
Do someone observed that after tank refill to full the fuel consumtion is low until fuel level drops to ~ 50% or less of tank capacity if from fillinng of tank  2 weeks or more have passed ?
But if refill to full tank after 1 or 2 bars disappear the MPG is good.

[guest10626]

This morning I observed a faster drop of the remaining kilometers value shown on the display while reaching the low fuel limit. It's just a feeling, but from full tank to empty tank the value of the remaining kilometers seem to change non linear. Sorry, it's difficult to explain in English. Do you know what I mean?

[nowster]

It's quite usual for the fuel gauge to start to move faster once it's below the half way mark. In some models it's due to the shape of the fuel tank.

[guest9814]

My question is not about non linearity of fuel meter gauge, but about say starting full tank with 3.3l/100km for about ~ 100 km but after 2 or more weeks and half of tank when driving same roads with same speed and driving habits you getting lower fuel economy let’s say 3.7l/100km when you approach to near empty tank.

I driving only 15 to 30 km /day so full tank can last up to 50 days with my current fuel economy.
I seen several times this fuel economy phenomenon but if I not waiting too long for refuel the fuel economy more stable
I think that may be because of how gasoline made - it have usually 2 or 3 components 1 of them is base with octane 70
Then to give more  high octane number this base blends  with higher octane components, but if fuel sits too much time in car tank and outside temperature relatively high  that high octane components evaporates and engine need to deal with lower octane fuel - engine will work also with fuel with octane 92 but how much fuel will eating for same distance ?

[sportse]

The miles remaining definitely disappears faster over the final 50 miles range left or so.

My first full tank I was running down and thought there was plenty for the journey but I had to drive slower with econ selected to make it to a closer petrol station than I had planned on.

[Kremmen]

My tank rarely gets below 50% as that's my trigger to top up.

Always like to have over half a tank, just in case.

[Neil Ives]

I first started driving in 1967, my first car was a 1929 Austin Seven, but I took it off the road to restore it, (a project that took 20 years. See picture) . My next three cars were Morris Minors, two split-windscreen convertibles and then a van*. Not earning very much money filling the petrol tank just didn't happen; I'd buy a few gallons at a time. When the fuel was getting low in the tank I could hear the sound of the electric fuel pump that was mounted on the bulkhead inside the engine bay start to tick as it sucked air. As the fuel got lower the speed of the ticking would increase. To get to the next petrol station I would swerve the car to one side so that a wave of petrol would cover the pump inlet tube in the tank. The ticking would stop for a while and then come back, busier than ever. Happy innocent days 

*The Morris Minor pictures are not of my cars.

[Jazzik]

My tank rarely gets below 50% as that's my trigger to top up.

Always like to have over half a tank, just in case.

This is how you increase your consumption ⛽  by driving around with unnecessary weight...

[guest9814]

Not with hybrid car !!!
More weight = better regenerative breaking 

[Downsizer]

The miles remaining definitely disappears faster over the final 50 miles range left or so.

My first full tank I was running down and thought there was plenty for the journey but I had to drive slower with econ selected to make it to a closer petrol station than I had planned on.

but there'll be a good safety margin after Zero miles remaining is reached - 2-3 litres I would think.

[guest4871]

 I thought the increasing rate of decline was something to do with Hysteresis affecting the float in the petrol tank.

Not really my subject.

Others may know better.

https://en.wikipedia.org/wiki/Hysteresis

[guest4871]

I first started driving in 1967, my first car was a 1929 Austin Seven, but I took it off the road to restore it, (a project that took 20 years. See picture) . My next three cars were Morris Minors, two split-windscreen convertibles and then a van*. Not earning very much money filling the petrol tank just didn't happen; I'd buy a few gallons at a time. When the fuel was getting low in the tank I could hear the sound of the electric fuel pump that was mounted on the bulkhead inside the engine bay start to tick as it sucked air. As the fuel got lower the speed of the ticking would increase. To get to the next petrol station I would swerve the car to one side so that a wave of petrol would cover the pump inlet tube in the tank. The ticking would stop for a while and then come back, busier than ever. Happy innocent days 

*The Morris Minor pictures are not of my cars.

Was1929 the last year the Austin Seven had the petrol tank over the engine?

[guest10626]

The miles remaining definitely disappears faster over the final 50 miles range left or so.

My first full tank I was running down and thought there was plenty for the journey but I had to drive slower with econ selected to make it to a closer petrol station than I had planned on.

but there'll be a good safety margin after Zero miles remaining is reached - 2-3 litres I would think.

Yesterday, I risked everything for my esteemed Clubjazz community. I filled up my car's tank with only 5 remaining kilometers on the meter.

[Kremmen]

So how many litres did you get in ?

The tank is 40L so it's interesting as to how many litres left  = 5 km

[ColinB]

I'm quite surprised that folks are prepared to believe the "range remaining" display and risk running out of fuel. Plenty of people have commented on the inaccuracy of the fuel economy calculation (aka the "fibometer"), and that data must be used in the range calculation. I have witnessed myself the range display (in my Mk 3) varying by +/- 30 or 40 miles whilst travelling only a few miles, so it's really not particularly accurate. But yet people are prepared to trust that they can travel 5km when the display says they can. I really don't get that.