Mpg trip computer accuracy

[Lamboluke]

Maths isn't my strong point so let's not make this about math skills and rather the accuracy of the trip comp.

So far since refuelling I've done 387 miles and the range is 25 miles (I am aware range has to be taken with a pinch of salt). The fuel gauge is showing 50:50 in the red.

Call the total miles 405 give or take on 50 litre of fuel according to the mpg calculator I'm using shows 36.8mpg, yet the computer is showing 44mpg.

Where is the discrepancy coming from?

Edited 7 February, 2014 by Lamboluke

[Lamboluke]

Just filled up and it's only taken 42 litres so maybe that's why?

[Keith64]

lol..i was just doing the maths....all your figures are correct 

[Lamboluke]

Yeah same. Just factored in that I've only used 42 litre to fill up.

I'm not going crazy then. Wonder why 8 litres remaining showing so low on range and on the fuel gauge. Hmm

[Keith64]

Wonder if it's a safety reserve?

[Smeghead]

Wonder if it's a safety reserve?

Only one way to find out  

[TheWanderer]

Well I don't trust it because for a tank that's meant to hold a maxima of 50l, I successfully managed to get 50l in when the fuel gauge was showing ¼ tank, I think I'll be having to have a word with the dealer unless they fitted a larger tank to my car, 

[Lamboluke]

8l seems a lot for a reserve to me. That being said knowing my luck I'll push it further next time, run out and end up filling it with 50 haha

[Neily03]

The reserve according the to manual is 7litres. Trouble is the fuel gauge on these is way out, when it says it empty it's far from it, I've ran the gauge to the bottom and only managed to get 45litres in...

[Lamboluke]

The reserve according the to manual is 7litres. Trouble is the fuel gauge on these is way out, when it says it empty it's far from it, I've ran the gauge to the bottom and only managed to get 45litres in...

I stand corrected. You would think these days they would be able to make the fuel gauge very accurate. Obviously not.

[themanwithnoaim]

Did the car come to a grinding halt having spluttered to death, no

Did it cost you any money to have the car recovered, no

Did it cause you any inconvience, no

You filled up before you ran out of fuel, yes

Realistically, I'd say the fuel gauge did its job, I really don't remember the last time I got out my micrometer to evaluate the exact amount of fuel I had left in order to calculate whether I could get to work and back again without filling up. Especially, when the computer display in front of me said 25 miles, I know there's probably a bit more but, unless I'm rushing my pregant wife to hospital its convential wisdom to just fill up. Its been this way for years, why is now a problem ?

If you don't believe your computer to do the fuel averaging for you, use fuelly.com

Has anyone every noticed how their speedo ain't exactly right compared to their GPS driven device well, what do you think works out the mileage and therefore, the fuel average, its gotta be out, the speedos are right.

Just my tupennies worth though

Regards

T

[Lamboluke]

Did the car come to a grinding halt having spluttered to death, noDid it cost you any money to have the car recovered, noDid it cause you any inconvience, noYou filled up before you ran out of fuel, yesRealistically, I'd say the fuel gauge did its job, I really don't remember the last time I got out my micrometer to evaluate the exact amount of fuel I had left in order to calculate whether I could get to work and back again without filling up. Especially, when the computer display in front of me said 25 miles, I know there's probably a bit more but, unless I'm rushing my pregant wife to hospital its convential wisdom to just fill up. Its been this way for years, why is now a problem ?If you don't believe your computer to do the fuel averaging for you, use fuelly.comHas anyone every noticed how their speedo ain't exactly right compared to their GPS driven device well, what do you think works out the mileage and therefore, the fuel average, its gotta be out, the speedos are right.Just my tupennies worth thoughRegardsT

I don't think it's too much to ask for the fuel gauge to be accurate and be a true reflection of the amount of fuel remaining in the tank.

Yes the range needs to be taken with a pinch of salt as individual driving styles and road conditions (plus a load more variables) have a huge effect.

Having an accurate gauge is important. If all fuel gauges fitted were accurate then people would actually pay attention to them rather than thinking hmmm it shows 10% left but actually I have 30% left.

Edited 7 February, 2014 by Lamboluke

[Smeghead]

Easy one to argue both ways...

 

• Accurate gauge and you will risk running out when it hits the bottom.  Not good, but at least you know what the score is so can plan accordingly.
• Inaccurate fuel gauge and you fill up before you need to (OK in normal life on roads you know but not so good on a long trip when you are not sure where the next garage will be / will it be open / will I get there?) meaning a 7 litre reserve is, in effect, a useful tank capacity of 43 litres (9 1/2 gallons for those of us who still speak English).

 

More old fashioned advice....keep a gallon can in the boot, just in case

[WeirdKerr]

The Fuel gauge on my Seat is annoying as it's digital bars (8 of them) and from full to the first bar going out is 200 or so miles second bar goes out after a shorter mileage though...  and at half is about 300  so each bar is less miles before going out which I find odd  and a few weeks back I managed more than 50 L on the final bar with fuel light on (think its the same size tank as an octy)

[Tramell]

In general I would agree that you should never let your car run out of fuel.  However, the last couple of times I have been driving back to the UK from the French Alps (a 500 mile trip) I would dearly love to know fairly accurately how far I can travel on whatever is left in my tank when it reads empty.

 

All I can say is that when you have had the car for a while you will get a feel for how many miles you can do when your gauge is approaching empty, make sure you are carrying a can of fuel and let the car run out a few times - that has worked for me in the past.

[C4miles]

 Has anyone every noticed how their speedo ain't exactly right compared to their GPS driven device 

 

Hmm. My boat's GPS used to tell me regularly that I was sailing 300 feet above sea level....

[Tramell]

Hmm. My boat's GPS used to tell me regularly that I was sailing 300 feet above sea level....

Did you ever try calibrating your GPS?  I have a Garmin GPS (that I use on land).  I believe that it uses atmospheric pressure to report altitude since triangulation based on satellites isn't accurate enough.  Once calibrated it seems to tally pretty closely with OS maps.

 

I have used it and two other GPS devices to check my TomTom and they all give almost identical speed readings - 75 mph on the speedo is 70 mph actual, etc.  I use my TomTom to give me an accurate speed reading almost as much as for navigation, particularly on the Continent with kph.

 

Incidentally, why on earth would a marine GPS even need to report altitude??

[andyvee]

I have managed to go the best part of 50 miles after the range read zero, and I could still only get 47 litres in. There is at least a gallon left when the range reads zero.

Sent from my phone so please excuse brevity and spelling

[themanwithnoaim]

Did you ever try calibrating your GPS?  I have a Garmin GPS (that I use on land).  I believe that it uses atmospheric pressure to report altitude since triangulation based on satellites isn't accurate enough.  Once calibrated it seems to tally pretty closely with OS maps.

 

I have used it and two other GPS devices to check my TomTom and they all give almost identical speed readings - 75 mph on the speedo is 70 mph actual, etc.  I use my TomTom to give me an accurate speed reading almost as much as for navigation, particularly on the Continent with kph.

 

Incidentally, why on earth would a marine GPS even need to report altitude??

Thats what I'm taking about, forget the fuel gauge being inaccurate, the speedo being inaccurate can get you points and in this game Bruce, points don't make prizes, what will be interesting to see is, if the Amundsen in my Elegance will show a different speed to the speedo.  But of course, if the speedo reads high so, will the mileage and therefore, your fuelly.com figures are going to be out as well,

 

Oh Fn hell, its a big boat, why rock it.

 

Regards

T

[andyvee]

The speedo reads high to try ans stop you getting points.

 

Just because the speedo reads 35, it doesn't mean it is logging the distance travelled at 35mph. The ECU knows the car is doing 31 (or whatever it is) but the speedo displays 35.

 

Don't over think it  :think:

[C4miles]

Did you ever try calibrating your GPS?  

Incidentally, why on earth would a marine GPS even need to report altitude??

 

Hi Tramell, that is a good point. 

 

Point 1 - Basically, I couldn't be arsed.

Point 2 - Quite. 

[ozoccy]

Filled mine with gauge on zero and about 10km left to empty and it took 51 litres.

[andyvee]

Not bad for a 50l tank, looks like you need to find a filling station with accurate pumps :-)

Sent from my phone so please excuse brevity and spelling

[Lamboluke]

I would imagine the filler neck and pipes may amount to a litre

[Dr Zoidberg]

I just filled mine for the second time, so first full tank used, and only put around 41 litres in, same as before. It seemed pretty full to me, bubbling up to the neck.

The gauge was just into the red, which starts at an eighth of a tank but it was warning me to refuel with 35 miles range, so something isn't quite right. I know no car has a fully linear gauge but this is either really distorted when low or very cautious so you don't run out.

How low have other owners taken it?

On the upside, I did 490 miles which is around 54mpg. Very close to the trip computers claim which is nice. Will see how it goes over the next few tanks.