Author Topic: 0 range but only 37.53 ltrs filled.... why?  (Read 5048 times)

JazzyJJ

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0 range but only 37.53 ltrs filled.... why?
« on: July 05, 2018, 09:31:42 PM »
This im sure has been asked before but ill ask again.

I got to 0 miles "range" left in the tank through unexpected traffic + detours after a long trip..  but luckily managed to get to petrol station which was 0.3 miles away.

Anyway, I think the tank capacity is either 42 or 40 yet I couldn't get anymore than 37.53 litres in - why is that? MY previous fill ups have been 36, 34, 37 and 36 ... each time I have been on the fuel warning light.

Do Honda leave the 5-2.5 ltrs as emergency reserve?

andruec

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #1 on: July 05, 2018, 09:52:44 PM »
The fuel tank capacity is 40 litres. So at most you had 2.5 litres in reserve. That's enough to drive ~25 miles. If they have designed the fuel system to keep a reserve then I'd say it's a bit low. I think having a litre left when the car says 'zero' would be better.

It's also worth noting that petrol expands in warm weather so that might mean less available space when filling up although I suspect forecourt fuel is at a more or less constant temperature so probably not a factor when the tank is almost empty.

But perhaps most significant is that you can't trust a car's fuel system to determine an accurate rate of consumption. The mpg and derived information are guesswork. Cars don't have an accurate way to measure fuel flow nor quantity in the tank. Fuel flow is estimated based on the duration that injectors are firing and is sampled periodically. Distance is estimated based on wheel rotation speed which depends on tyre wear and pressure (pressure being something that, again, is temperature dependant).

In simple terms: The distance remaining is an estimate as is the mpg display. The only thing we can be pretty sure about is that you put 37.53 litres in (because that is a verified measurement). Anything else is estimated.

Skyrider

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #2 on: July 05, 2018, 10:02:25 PM »
I don't play fuel gauge roulette and stress, I take quarter full as a hint it needs fuel soon.

Jocko

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #3 on: July 05, 2018, 10:06:40 PM »
In simple terms: The distance remaining is an estimate as is the mpg display. The only thing we can be pretty sure about is that you put 37.53 litres in (because that is a verified measurement). Anything else is estimated.
That is why the only accurate mpg figure is that calculated from the odometer reading and the measured amount of fuel put into the tank. The dashboard display is not called the "fibometer" for nothing.

MicktheMonster

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #4 on: July 06, 2018, 03:28:47 AM »
When I got my new jazz in January, salesmen told me when warning light first comes on you have about 8 litres left in the tank, but when it starts flashing fill it urgently, haven't ran it down to 0 miles so don't know what's left at that point, but it would be reasonable to expect them to leave you some margin for human error or distance to petrol stations etc.
Only one way to find out when it runs out of fuel, if anybody does it, let us know....

Jocko

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #5 on: July 06, 2018, 06:45:29 AM »
As I said elsewhere on this forum, I have driven 500 miles between refills. There seems to be a load of fuel left when the light first comes on.

JazzyJJ

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #6 on: July 06, 2018, 08:00:02 AM »
There is a guy on YouTube (prob many) who fills up a jerry can and drives until he runs out to see how many miles he gets after the fuel light came on. Not sure how much he got (was a lot) and it wasn’t a jazz (some old car).

Maybe someone with a mk3 should volunteer to do this as a service to forum users and add to the knowledge base ?  ;)
« Last Edit: July 06, 2018, 08:15:18 AM by JazzyJJ »

JazzyJJ

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #7 on: July 06, 2018, 08:03:33 AM »
When I got my new jazz in January, salesmen told me when warning light first comes on you have about 8 litres left in the tank, but when it starts flashing fill it urgently, haven't ran it down to 0 miles so don't know what's left at that point, but it would be reasonable to expect them to leave you some margin for human error or distance to petrol stations etc.
Only one way to find out when it runs out of fuel, if anybody does it, let us know....

I got to zero as I said and nothing was flashing. I’ll check the manual later if it says anything.

John Ratsey

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #8 on: July 06, 2018, 08:24:48 AM »
Having around 1/2 gallon remaining when the computer says 0 miles is reasonable. It could well be more than that if Honda excludes the volume of fuel in the filler pipe from the advertised tank capacity.

I found the miles remaining calculation on the Mk 3 to be a lot less conservative than on the Mk. 2.
2022 HR-V Elegance, previously 2020 Jazz Crosstar

culzean

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #9 on: July 06, 2018, 08:58:47 AM »
Having around 1/2 gallon remaining when the computer says 0 miles is reasonable. It could well be more than that if Honda excludes the volume of fuel in the filler pipe from the advertised tank capacity.

I found the miles remaining calculation on the Mk 3 to be a lot less conservative than on the Mk. 2.

Here is an interesting site ( USA unfortunately) seems the worst car is the Fiat 500 with barely 15 miles after fuel light comes on,  Honda and Toyota seem conservative with generally over 60 miles - now I know which one I would prefer at night in a strange area ( I would never let my fuel get below 1/4 tank anyway,  and I doubt my wife would but if it did happen and empty light came on and the fact that now in UK petrol stations are getting bigger but further apart as the smaller ones close down,  just like hospitals really).  Car companies build these cars for world markets and in quite a few countries it is a long way between fuel stations,  I would look on the fuel light as a reminder that I have been a dickhead and let the fuel get too low for comfort,  but I have only ever seen it come on in other peoples cars  :o  (except once when I did it deliberately seeing how many miles I could go on a tank until it came on).

https://tankonempty.com/findcar

But perhaps most significant is that you can't trust a car's fuel system to determine an accurate rate of consumption. The mpg and derived information are guesswork. Cars don't have an accurate way to measure fuel flow nor quantity in the tank. Fuel flow is estimated based on the duration that injectors are firing and is sampled periodically. Distance is estimated based on wheel rotation speed which depends on tyre wear and pressure (pressure being something that, again, is temperature dependent).

I have found that the more smoothly you drive,  avoiding rapid acceleration or braking the nearer the onboard MPG readout gets to MPG calculated by checking how much fuel goes into tank.  I guess this is due to the fact that the flow rate (from ECU and injector on time) and miles traveled are only sampled and updated with a snapshot of 'current usage' about every 10 seconds (and anything that happens between those snapshots will be ignored.  This 'sampling' is common in industry for flow and the higher the sampling rate the more accurate the result.  Another thing I have noticed is that when you first zero the trip the MPG figure can jump around a bit,  probably due to the fuel used figure being averaged out by the computer over a fairly small mileage on trip,  as the miles on trip increases the MPG readout gets slower and slower to respond to changes in driving behaviour as the rate of fuel usage gets averaged out over a larger mileage reading. If you let the trip mileage build up and zero it every time you fill up (as I do) you notice that the MPG figure does not really change much when trip gets over 100 miles ( on the Civic there is an 'instantaneous MPG readout,  and that jumps around like crazy all the time).

« Last Edit: July 06, 2018, 09:27:37 AM by culzean »
Some people will only consider you an expert if they agree with your point of view or advice,  when you give them advice they don't like they consider you an idiot

andruec

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #10 on: July 06, 2018, 10:07:29 AM »
As I said elsewhere on this forum, I have driven 500 miles between refills. There seems to be a load of fuel left when the light first comes on.
Not as much as on the Mk2 and Mk1. I think their lights used to come on where there was two gallons left in the tank!

ColinB

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #11 on: July 06, 2018, 10:08:09 AM »
This im sure has been asked before but ill ask again.

I got to 0 miles "range" left in the tank through unexpected traffic + detours after a long trip..  but luckily managed to get to petrol station which was 0.3 miles away.

Anyway, I think the tank capacity is either 42 or 40 yet I couldn't get anymore than 37.53 litres in - why is that? MY previous fill ups have been 36, 34, 37 and 36 ... each time I have been on the fuel warning light.

Do Honda leave the 5-2.5 ltrs as emergency reserve?
Some time ago I reported on the variability of the range estimation by the car’s computer:
https://clubjazz.org/forum/index.php?topic=8559
Basically, it was all over the place, my overall conclusion was that you shouldn’t expect any sort of accuracy from it and certainly shouldn’t trust it. So if you reached zero on the range display without getting a low fuel warning (I think that’s what you’re saying ?) I would suspect the range calculation rather than the fuel level.

But, as others have said, why cause yourself stress by not filling up ?

JazzyJJ

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #12 on: July 06, 2018, 01:18:31 PM »
So if you reached zero on the range display without getting a low fuel warning (I think that’s what you’re saying ?) I would suspect the range calculation rather than the fuel level.

But, as others have said, why cause yourself stress by not filling up ?

The warning light had come on and I was on the motorway and.. see below..

I didn’t intentionally cause myself stress. Everything was looking fine for my return journey home but towards the end there was UNEXPECTED heavy traffic and my sat nav ie. waze app took me on a detour to avoid sitting in traffic for hour+ and because of that I just continued as the app ‘miles to home’ was less than the range but it started to get tight the more i drove and by the time it was down to 2 miles i was close to home and I knew where the closet petrol station was. Just a number of factors converging. Normally I would have filled up sooner.

« Last Edit: July 06, 2018, 01:28:06 PM by JazzyJJ »

Skyrider

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #13 on: July 06, 2018, 03:47:50 PM »
So if you reached zero on the range display without getting a low fuel warning (I think that’s what you’re saying ?) I would suspect the range calculation rather than the fuel level.

But, as others have said, why cause yourself stress by not filling up ?

The warning light had come on and I was on the motorway and.. see below..

I didn’t intentionally cause myself stress. Everything was looking fine for my return journey home but towards the end there was UNEXPECTED heavy traffic and my sat nav ie. waze app took me on a detour to avoid sitting in traffic for hour+ and because of that I just continued as the app ‘miles to home’ was less than the range but it started to get tight the more i drove and by the time it was down to 2 miles i was close to home and I knew where the closet petrol station was. Just a number of factors converging. Normally I would have filled up sooner.

So just your poor planning then. Heavy traffic and motorway accidents, delays etc. are a fact of life in the UK. Electronic gadgets are only an aid to travelers, they frequently get  it wrong. When l travel long distances on motorways or in winter I always have a contingency reserve, in severe winter weather in remote areas your life may depend on it. A car uses about 0.2 of a litre per hour when idling.

Re: 0 range but only 37.53 ltrs filled.... why?

It's not accurate! A bit like your Waze, and all other traffic and satnav systems, they are only a guide not necessarily accurate.
« Last Edit: July 06, 2018, 09:56:43 PM by Skyrider »

VicW

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Re: 0 range but only 37.53 ltrs filled.... why?
« Reply #14 on: July 06, 2018, 07:41:35 PM »
The fuel tank in the Jazz is under the two front seats and is very shallow hence it is difficult to have a very accurate level sensor using a level float on an arm as is normal.There are other ways of measuring fuel level but they are expensive. Consequently the gauge is not very accurate when the fuel level is low so the low level light is pessimistic.
It's not wise to let the tank get very low on fuel very often as there is a danger of dragging the crud in the tank into the filter.

Vic.

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