Sudden loss of "miles to empty" towards the end of a tank

Sanzomat · Oct 7th, 2009, 14:12

I'm starting to see a trend developing and was wondering if others cars do the same.
After filling up and driving a few miles to settle the computer my "range" usually settles to somewhere around 700 miles (2.0d V70 RD) and as i use the fuel it stays the same (i.e. sum of distance travelled and range left = 700) it goes up a bit after a period of really gentle driving and down a bit after some steep hills or acceleration but usually settles back to 700. The computer is usually saying about 44.4 mpg average during this time so that matches the 700 miles on a tank.
The only thing is that it tails off massively over the last 100 miles or so without my driving style changing at all. E.g. I set of for work yesterday with the range showing 140 miles (575 travelled since fill up), got to work, still showing 105 miles range (610 travelled) When I started the car to go home (thinking I better fill up tomorrow lunchtime) the range had dropped to 90. 25 miles later with ten miles left to home it was at 15 miles and then suddenly dropped to ---. Next opportunity to fill up was 10 miles later at which I put in 70.5 litres to the first click of the pump so my 70l tank must have been pretty empty. Also during that journey the average mpg dropped from 44.2 at the start of the journey to only 42.6 35 miles later (645 from the tank overall) by my sums this works out as 41.6 mpg so only 1 out from the computer figure but if I was truly at 44.2 (so say accurately 43.2) at 610 miles I must have used 6.5l to do 35 miles home so only 24.4 mpg. Something can't be right. I've noticed this on previous tanks too so I'm guessing the computer must over estimate for the first 90% of a tank then correct itself in the last bit.
The moral is you have to be very careful starting out on a journey thinking you still have 100 miles in the tank because the chances are you really only have less than 40!

Hinckley · Oct 7th, 2009, 15:57

The S80 i've just traded out did just that, never got 600 miles out of a tank though!
Last 100 miles to go was about 50 in reality and driving with --- miles to go is a tad worrying.
I think the computer is more of a guide than anything else - I never got more than £60 59ltrs worth of diesel in mine (£40 of petrol once hope I never do that again) and a brim to brim fill was three or four mpg less than the computer said.

Cheers,
Pip

Clan · Oct 7th, 2009, 19:17

Quote:

Originally Posted by Sanzomat

I'm starting to see a trend developing and was wondering if others cars do the same.
After filling up and driving a few miles to settle the computer my "range" usually settles to somewhere around 700 miles (2.0d V70 RD) and as i use the fuel it stays the same (i.e. sum of distance travelled and range left = 700) it goes up a bit after a period of really gentle driving and down a bit after some steep hills or acceleration but usually settles back to 700. The computer is usually saying about 44.4 mpg average during this time so that matches the 700 miles on a tank.
The only thing is that it tails off massively over the last 100 miles or so without my driving style changing at all. E.g. I set of for work yesterday with the range showing 140 miles (575 travelled since fill up), got to work, still showing 105 miles range (610 travelled) When I started the car to go home (thinking I better fill up tomorrow lunchtime) the range had dropped to 90. 25 miles later with ten miles left to home it was at 15 miles and then suddenly dropped to ---. Next opportunity to fill up was 10 miles later at which I put in 70.5 litres to the first click of the pump so my 70l tank must have been pretty empty. Also during that journey the average mpg dropped from 44.2 at the start of the journey to only 42.6 35 miles later (645 from the tank overall) by my sums this works out as 41.6 mpg so only 1 out from the computer figure but if I was truly at 44.2 (so say accurately 43.2) at 610 miles I must have used 6.5l to do 35 miles home so only 24.4 mpg. Something can't be right. I've noticed this on previous tanks too so I'm guessing the computer must over estimate for the first 90% of a tank then correct itself in the last bit.
The moral is you have to be very careful starting out on a journey thinking you still have 100 miles in the tank because the chances are you really only have less than 40!

I think as the tank gets lower the signal from the tank level sensor has much more of an effect ..

Remember though , that the main indication of fuel tank level is the fuel gauge thats why it is there !! And its very accurate at the low end ..

bornagain · Oct 7th, 2009, 20:02

My s60 t5 told me I had 40 miles left then 0 miles left within 5 miles. When I filled it up it took 69.75 litres, I do believe I have a 70 litre tank!

Penguinistics · Oct 7th, 2009, 20:05

My car does that as well and I suspect it has something to with the generally unusual shape that fuel tanks seem to have now such that they fit in well between the other components and don't impinge on load / passenger space. The will be some sort of fuel level sensor that has to cope with the fuel sloshing about as well as cope with variations in fuel tank cross section along it's scale. I wonder how clever the Volvo system is - can it take all this into account or does the gauge make approximations that just aren't true when the tank runs relatively empty. For me the fuel gauge light comes on neally 15 litres before the tank is empty (80 litre tank) which seems a tad risk averse on the part of the computer which seems to think that 15 litres also means less than 50 miles (which it doesn't - more like 90+). The most I ever fitted in was ~77 litres

Chris Parish · Oct 7th, 2009, 20:36

My S80 D5 2001 will actually do about 550-600 miles per tank full, or about 35-39 mpg average. The computer however says I need to fill up in 900 miles when I've just filled up and normally shows about 10mpg over the actual, i.e 45-49mpg. I enjoy resetting it on a motorway cruise and try to get it to stay around 70mpg for as long as possible, it can become obsessive though. Also, try resetting it just before a long steep hill and gun it up the hill, the consumption is frightening!

bornagain · Oct 7th, 2009, 20:46

Quote:

Originally Posted by Chris Parish

Also, try resetting it just before a long steep hill and gun it up the hill, the consumption is frightening!

I can get 4 mpg with a heavy right foot, now thats fun!

Clan · Oct 7th, 2009, 22:06

Thats nothing , The mitsubishi Lancer EVO's racing in the castle combe modified saloon car championsip use 75 litres in 12 laps ( 12 x 1.8m miles ) !

avtur · Oct 14th, 2009, 00:09

Sanzomat, my experience is exactly in line with yours, getting quite used to it now. Have had the cumulative figure (range plus miles since full) up around 800 a couple of times, but it never maintains all the way down the tank! A few years back I had a Pug 406 HDI, think that was 70l tank and managed to top 950 miles actual before filling up on several occasions - never quite made the magic 1000 though.

Have just managed the best so far on the V70 at 730 miles with a 66 litre fill up, quite happy with that on a car of its size.

Oct 7th, 2009, 14:12	#1
Sanzomat Member Last Online: Mar 16th, 2017 22:26 Join Date: May 2009 Location: Bristol	Sudden loss of "miles to empty" towards the end of a tank I'm starting to see a trend developing and was wondering if others cars do the same. After filling up and driving a few miles to settle the computer my "range" usually settles to somewhere around 700 miles (2.0d V70 RD) and as i use the fuel it stays the same (i.e. sum of distance travelled and range left = 700) it goes up a bit after a period of really gentle driving and down a bit after some steep hills or acceleration but usually settles back to 700. The computer is usually saying about 44.4 mpg average during this time so that matches the 700 miles on a tank. The only thing is that it tails off massively over the last 100 miles or so without my driving style changing at all. E.g. I set of for work yesterday with the range showing 140 miles (575 travelled since fill up), got to work, still showing 105 miles range (610 travelled) When I started the car to go home (thinking I better fill up tomorrow lunchtime) the range had dropped to 90. 25 miles later with ten miles left to home it was at 15 miles and then suddenly dropped to ---. Next opportunity to fill up was 10 miles later at which I put in 70.5 litres to the first click of the pump so my 70l tank must have been pretty empty. Also during that journey the average mpg dropped from 44.2 at the start of the journey to only 42.6 35 miles later (645 from the tank overall) by my sums this works out as 41.6 mpg so only 1 out from the computer figure but if I was truly at 44.2 (so say accurately 43.2) at 610 miles I must have used 6.5l to do 35 miles home so only 24.4 mpg. Something can't be right. I've noticed this on previous tanks too so I'm guessing the computer must over estimate for the first 90% of a tank then correct itself in the last bit. The moral is you have to be very careful starting out on a journey thinking you still have 100 miles in the tank because the chances are you really only have less than 40!

Oct 7th, 2009, 15:57	#2
Hinckley Member Last Online: Nov 14th, 2011 16:42 Join Date: Feb 2009 Location: Silverstone	The S80 i've just traded out did just that, never got 600 miles out of a tank though! Last 100 miles to go was about 50 in reality and driving with --- miles to go is a tad worrying. I think the computer is more of a guide than anything else - I never got more than £60 59ltrs worth of diesel in mine (£40 of petrol once hope I never do that again) and a brim to brim fill was three or four mpg less than the computer said. Cheers, Pip __________________ Had 1981 265 GLE V6 Had 2003 S60 20T SE Had 2008 S80 D5 LUX Too many electrical problems Last 2009 Merc CLS Now 2004 S80 2.5T SE + Freelander! (BOGOF!)

Oct 7th, 2009, 20:02	#4
bornagain Speed freak Last Online: Apr 18th, 2014 09:00 Join Date: May 2009 Location: Egahm,Surrey	My s60 t5 told me I had 40 miles left then 0 miles left within 5 miles. When I filled it up it took 69.75 litres, I do believe I have a 70 litre tank! __________________

Oct 7th, 2009, 20:36	#6
Chris Parish Large Member Last Online: Jun 2nd, 2013 14:25 Join Date: Dec 2008 Location: Rochester	My S80 D5 2001 will actually do about 550-600 miles per tank full, or about 35-39 mpg average. The computer however says I need to fill up in 900 miles when I've just filled up and normally shows about 10mpg over the actual, i.e 45-49mpg. I enjoy resetting it on a motorway cruise and try to get it to stay around 70mpg for as long as possible, it can become obsessive though. Also, try resetting it just before a long steep hill and gun it up the hill, the consumption is frightening! __________________ Currently: S60 T S 2001 and S80 D5 2002 Previously: 245 and V70 T5

Oct 7th, 2009, 22:06	#8
Clan Experienced Member Last Online: Today 00:05 Join Date: Jun 2007 Location: L/H side	Thats nothing , The mitsubishi Lancer EVO's racing in the castle combe modified saloon car championsip use 75 litres in 12 laps ( 12 x 1.8m miles ) ! __________________ My comments are only based on my opinions and vast experience .

Oct 7th, 2009, 20:05	#5
Penguinistics VOC Member Last Online: Nov 20th, 2021 22:30 Join Date: Apr 2009 Location: Preston	My car does that as well and I suspect it has something to with the generally unusual shape that fuel tanks seem to have now such that they fit in well between the other components and don't impinge on load / passenger space. The will be some sort of fuel level sensor that has to cope with the fuel sloshing about as well as cope with variations in fuel tank cross section along it's scale. I wonder how clever the Volvo system is - can it take all this into account or does the gauge make approximations that just aren't true when the tank runs relatively empty. For me the fuel gauge light comes on neally 15 litres before the tank is empty (80 litre tank) which seems a tad risk averse on the part of the computer which seems to think that 15 litres also means less than 50 miles (which it doesn't - more like 90+). The most I ever fitted in was ~77 litres

Oct 14th, 2009, 00:09	#9
avtur Member Last Online: Jun 28th, 2010 00:20 Join Date: Jan 2009 Location: Stockport	Sanzomat, my experience is exactly in line with yours, getting quite used to it now. Have had the cumulative figure (range plus miles since full) up around 800 a couple of times, but it never maintains all the way down the tank! A few years back I had a Pug 406 HDI, think that was 70l tank and managed to top 950 miles actual before filling up on several occasions - never quite made the magic 1000 though. Have just managed the best so far on the V70 at 730 miles with a 66 litre fill up, quite happy with that on a car of its size. Last edited by avtur; Oct 14th, 2009 at 00:12. Reason: ooops!

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