Low fuel range and the onboard computer

John_B

John_B

Zorg Guru (II)
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British Zeds
The M44 Massive
Joined
Jun 2, 2023
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Location
Derbyshire, UK
Come on then brain-trust, one of you must know the rough remaining range when the computer says zero.

The reason I ask is because I have just finished a long trip in the Z3, and the range anxiety was killing me every time the low fuel light came on. One time in particular the range computer was down to 12 miles, but brimming the tank only added 43 litres - it's a 51 litre tank, meaning there should still have been 8 litres in there.

Based on getting about 300-330 miles out of those 43 litres before I'd be filling up again, that means there is theoretically another 60 miles in the tank, when the range computer said 12 - Does that sound right? And that means from the low-fuel light coming on, there would be nearly 100 miles of range, more than a quarter of tank!

I'm almost tempted to fill a jerry can and find a safe stretch of motorway or dual carriageway to experiment on!
 
I have not got a 'range computer' in my car but I've always reckoned on about 5 litres or about 30 miles once the light comes on.
 
The range computer works on the latest minute or so of consumption, so if you boot it out of a junction, watch it drop rapidly. If you then proceeded to coast downhill you’d see that the range ‘magically’ increases
 
Years ago in a Z3, I ran it to 0 in the computer and there was still fuel left; don't know how much though. Only way to really test is carry a fuel can and run the car tank it dry! Suggest not on a motorway though!!
 
GZed said:
The range computer works on the latest minute or so of consumption, so if you boot it out of a junction, watch it drop rapidly. If you then proceeded to coast downhill you’d see that the range ‘magically’ increases
Click to expand...

I don't think it is based on such a short window otherwise it would be all over the place and pretty meaningless. Maybe the last hour perhaps? However, regardless, for it to say 12 miles remaining when there must have been at least 8 litres remaining works out at like 6 MPG 😅 In this case we were getting around 29 over that particular tank and 30.8 since the last trip reset

There is clearly a significant reserve built into the range calculation, which is what I am trying to establish. I'm just staggered that it could be so large (proportionally) in a small tank
 
John_B said:
Come on then brain-trust, one of you must know the rough remaining range when the computer says zero.

The reason I ask is because I have just finished a long trip in the Z3, and the range anxiety was killing me every time the low fuel light came on. One time in particular the range computer was down to 12 miles, but brimming the tank only added 43 litres - it's a 51 litre tank, meaning there should still have been 8 litres in there.

Based on getting about 300-330 miles out of those 43 litres before I'd be filling up again, that means there is theoretically another 60 miles in the tank, when the range computer said 12 - Does that sound right? And that means from the low-fuel light coming on, there would be nearly 100 miles of range, more than a quarter of tank!

I'm almost tempted to fill a jerry can and find a safe stretch of motorway or dual carriageway to experiment on!
Click to expand...

Don't put the jerry can in the boot ----- since that's where the battery lives!
 
There are some old threads on this topic. My average tank to tank consumption is pretty consistent, so work on that basis as I don’t have a trip computer. I plan on filling up every 250 miles. At that stage it’s normally very close to the low fuel warning coming on, but with some margin to drive around to find fuel without any anxiety.
 
Chad66Wick said:
Don't put the jerry can in the boot ----- since that's where the battery lives!
Click to expand...
Most cars have their battery in the engine bay------where all the sparks and bangs happen! :)
 
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