are mpg computer accurate,im getting bad mpg

[GingerMagic]

Can I throw my tuppence in too??
When I first got my Hdi90, I was getting a disappointing 40mpg round town and 45mpg on a run. I drive like a blind pensioner so I couldn't understand why so low. Now I have learned that it is not engine revs that matter, its the throttle position on my car. Try it, get to around 2ooorpm as usual but lift of the throttle slightly. Revs don't drop much but mpg goes up a bit. I think I used to labour the engine too much - despite being a diesel - which used fuel too.
Now I get 48mpg round town and 55mpg on a run, momentum is useful on the underpowered 90......
There is a calculation you can use to check your mpg, just to see if trip computer is accurate, here it is:
Remember what you paid per litre, arguements sake say £1.50.
If you put in £50, divide this by £1.50 to say how many litres used ( 33.33 )
Divide 33.33 by 4.54, this tells you how many gallons you have used ( 7.34 )
Next, divide the miles you did by 7.34 e.g 320 miles, works out at 43.5mpg.
I normally get 650miles on a tank full, another 40 with the light on.....!!
Hope this is useful ???

[waue1978]

Much simpler (& probably more accurate) just to use miles divided by litres x 4.546 resetting the trip counter on the dash each time you fill it up.

[codgod]

hi folks,since my posting i have done 3 brim to brim tests,1st test i drove for 40 miles on motorway then another 80 urban 120 in total results were 45 mpg.2nd test drove for 140 miles urban results 38.5 mpg.3rd test drove for 182 miles results 39 mp the mpg computer was more or less correct each time.results were done by calculating fuel used by calculator,are these results ok or should i be getting better.the car is a y reg 2.0hdi 110 exec estate 156,000 on clock.i have just filled up again after the 3rd test because i feel that my fuel gauge could be faulty,the needle was a nats penis just below the half way notch after 182 miles surely thats not right.the one thing i notice with this car is that the fuel gauge heads south pretty rapidly.could my fuel sender be faulty.

[GingerMagic]

Maybe your gauge is faulty, you can cover around 350 miles on the top-half of a tank if you are careful.
On two occasions my gauge ( and trip computer ) has lost a quarter of a tank of fuel, saying I have much less than when I turned the engine off 20 mins earlier, only to give it back a few days later.....!!
I suppose the best way to tell would be to see how much money fills the tank, maybe £90 or so, the fill it up when you get down to half a tank. If it costs £50 for top up, then gauge is fine. If it costs £20 then gauge is bummed....
If its any consolation, its better mpg in the summer!

[k_f]

The trip computer on my petrol V6 is very accurate. MPG on a run is mid-30s which is very good for such a large engine with an autobox.

[codgod]

Maybe your gauge is faulty, you can cover around 350 miles on the top-half of a tank if you are careful.
On two occasions my gauge ( and trip computer ) has lost a quarter of a tank of fuel, saying I have much less than when I turned the engine off 20 mins earlier, only to give it back a few days later.....!!
I suppose the best way to tell would be to see how much money fills the tank, maybe £90 or so, the fill it up when you get down to half a tank. If it costs £50 for top up, then gauge is fine. If it costs £20 then gauge is bummed....
If its any consolation, its better mpg in the summer!

hi gingermagic,thanks for getting back to me.when if filled the car back up for the 3rd time it had half a tank left in it.it cost me £31 to fill it back up,do you think its knackered or what.can i just replace the float or do i have to change the complete sender unit with pump.

[GingerMagic]

Hi codgod, to be fair I know nothing of the sender units as I am only a basic fair weather mechanic not really a specialist. Floats don't normally go wrong as it is just something that floats, but you could look at the sender units wiring and general condition before taking the plunge and replacing it. However if you are still getting around 600 miles per tank - even if the top half rapidly drops and the bottom half goes slow - then I would leave it and exept it is a quirk of the car. Your trip computer is accurate enough to get along with. 40 - 45 mpg around town is perfectly acceptable.

[pavlf]

I did a brim to brim test on my 02 110 rapier estate and got 31mpg doing short journeys around town. Computer said 31.7 mpg. This seems pretty terrible to me! I went down the M6 on sunday, steady 75, occasionally up to 80 by accident, and got 45 on the computer. I felt a bit better but still think it's not right. Otherwise this car is fine. Recently serviced, and I ran some injector cleaner through it. I bought it to replace a 2.1 hoping to get better mpg, but in reality it's about the same, if not slightly worse. Any ideas if there might be 'something' causing this? The brakes aren't binding, so it isn't that.

Anyway, in the meantime I might put the computer display onto the date. I'm going to crash if I keep looking at the mpg!

[waue1978]

I did a brim to brim test on my 02 110 rapier estate and got 31mpg doing short journeys around town. Computer said 31.7 mpg. This seems pretty terrible to me! I went down the M6 on sunday, steady 75, occasionally up to 80 by accident, and got 45 on the computer. I felt a bit better but still think it's not right. Otherwise this car is fine. Recently serviced, and I ran some injector cleaner through it. I bought it to replace a 2.1 hoping to get better mpg, but in reality it's about the same, if not slightly worse. Any ideas if there might be 'something' causing this? The brakes aren't binding, so it isn't that.

Anyway, in the meantime I might put the computer display onto the date. I'm going to crash if I keep looking at the mpg!

That's only a little bit juicier than mine was. 31mpg doing short journeys isn't bad - most of my trips were cold starts of less than 5 miles. 45mpg on the motorway isn't too bad either. I know a lot of people say that they get 45 around town & 60 on the motorway, but Peugeot's quoted figures are only 37 around town & 60 something extra-urban (which means Sunday driver) & those figures are produced on rolling roads with computers controlling the car on simulations. If you're within reach of that, you haven't got too much to worry about.

[Doggy]

The engine characteristics will be quite different between the 2.1 & HDi 110. On my previous Xsara, it took me a month or two of steadily improving mpg to find the best technique, (which on a HDi 90 seemed to be a fair bit of throttle and change up early). IIRC I started at about 46 and wound up at 49/50 with a best tankful of 52 mpg.

[lozz]

ithink the xsara hdi, is very poor on mpg,
compared to the 406 hdi 110,

with the xsara, ithought less weight, it be alot cheaper to run, it was the other way around,

[pavlf]

OK, thanks for the comments. I now reckon mine is OK, I'm turning the display off. I think it encourages obsessive behaviour and makes me drive dangerously!

[GingerMagic]

Opposite for me, I loved to drive while staring at the trip computer to see how my driving increased mpg. I found getting speed up early and then feathering throtle worked for me. If I changed gear too early while accelerating it would labour too much. I do get 45mpg round town but then again there is normally a queue of milkfloats and tractors behind me itching to get past....

[lozz]

ithink pavlf is spot on there !


iwont even bother looking at the Mpg display again, too depressing,
and it makes one try to save on fuel, whats next Fork in sugar bowl ,

[GingerMagic]

Both Lozz ans Pavlf are right. Its nice to know what your car can achieve in mpg but don't let it stop you having a bit of fun while driving....
Nothing wrong with a fork in the sugar bowl, I've even told my little boy that if the ice-cream van is playing music - it means they have sold out..!!