Warm Weather MPG

[Ocularis]

Ok so my MPG is now much better... had fuelly set up wrong haha.



So now im 0.3 out from my on-board computer, that makes much more sense now ... Should have stuck to pen and paper!

 

[andrewpain]

should have trusted the on-board system
29mpg isn't bad at all for a Cupra in it's first flush of ownership!

 

[Luckypants]

I agree that the computer should be accurate because it knows the fuel pumped into the engine and the mileage. My calculations using the same mileage reading (trip/odometer) based on the fuel put in the tank should match. I keep track of it on fuelly, so will see if long term average on the computer matches fuelly. Tank by tank differences may be accounted for by differences in what I think is 'full'. I've only filled it three times so far and each one has shown the computer to be out by 2-3 mpg.

So back to this. Last tank of diesel gave a measured average of 54.54mpg (filled to the shut-off click, pause fill to next click) and the computer gave a 'since refuel' average of 58.4. The tyre pressures are spot on, so rolling circumference should be stable. The Long term average in the computer is showing 57mpg. This has exactly the same mileage as Fuelly, which gives a measured average of 53.8mpg. So the computer looks to be about 6% out on my car at the moment.

Anyone else able to comment on the accuracy of the computer versus what they measure as being put in?

 

[DaFoot]

I'm averaging ~50mpg over the 8k miles since I've had my 184 FR.
That's calculated, not from the car computer.

The car reckons I'm getting more like 53mpg.

Either way seems low to me

 

[Luckypants]

I'm averaging ~50mpg over the 8k miles since I've had my 184 FR.
That's calculated, not from the car computer.

The car reckons I'm getting more like 53mpg.

So about 6% out like mine

Either way seems low to me

But not bad for 184bhp motor!

 

[DaFoot]

Given one of reasons I chose Leon was for the 60+ mpg it will remain a disappointment I that regard.

 

[Deleted member 98136]

Given one of reasons I chose Leon was for the 60+ mpg it will remain a disappointment I that regard.

Know what you mean, before getting my Leon, I was leaning towards a Fiesta with auto box
and what was claimed to be frugal MPG,
But after reading thro' a lot of the posts on their forums, it became evident that numerous owners commented on auto gearbox issues and several commented on poor fuel economy based on the manufactuers quoted figures, especially on the less powerful engines in the range, which was what I wanted.

With the Leon, I can't say I've experienced any hint of a problem with the DSG box and the MPG is getting better the more I drive.

 

[DEAN0]

Given one of reasons I chose Leon was for the 60+ mpg it will remain a disappointment I that regard.

I have found that over the various cars ( mk4 Ibiza 130TDi, Mk5 Ibiza 143TDi and now Leon 184TDi ) - it is getting harder to achieve even close to the quoted MPG numbers.

Every year they claim better efficiency from the engines but in reality the newer numbers are a crock

 

[Luckypants]

I'm well aware of the difference between the figures published for the purposes of CO2 banding, marketing etc and the real world. Living in a hilly area I would never expect to get the same MPG as the manufacturer 'proves' in a laboratory - but we should be able to get close! Seems unlikely with whatever method they use to get these figures though!

So while I expect to not get the claimed 70-odd mpg from my Leon, I would like the on-board computer to be accurate!

 

[andrewpain]

yes - you'd expect the on-board system to be accurate.
manufacturers figures for emissions and consumption are all based on calculations of throttle openings, gear ratios, projected friction, wind resistance etc, from a single rolling road lab test at a constant throttle.
They don't get them from actual road tests.
The EU authorities set out how they have to calculate everything, so it's not even the car makers fault.
It's the damn European commission.
again...

 

[DaFoot]

To be fair, it's good that the test is at least standardised. At least then we've some guide figures for comparisons.

Doesn't change the frustration they are so far away from real values.

 

[Seastormer]

To be fair, it's good that the test is at least standardised. At least then we've some guide figures for comparisons.

That's all I have ever used it for.

 

[andrewpain]

it's all you CAN do, I think.
although I'm close to the claimed figures much of that is because I drive like a chauffeur and I'm a cheapskate.
it's easy to get 55mpg out of a 184 under those circumstances. And I think 55 is good.

 

[Luckypants]

So just to add a bit more evidence to how unrealistic the MPG figures from the computer are, my last tank the computer said 58.9 mpg since refuel while the calculated average from Fuelly is 52.51! Is the trip computer getting even more inaccurate?

As a corollary to that, the 'range to empty' and fuel low warning lights are wrong too. At the last fill the fuel warning light had just come on and range was predicting 55 miles, but the tank only took 42.6 litres. This means there was at least 7.4 litres left in the tank so at my true mpg figure I had 85 miles left but on the computer's mpg figure it should have calculated I had 95 miles left!

Something is not quite right with the trip computer, shame really as if it was accurate it would be really useful!

 

[Seastormer]

So just to add a bit more evidence to how unrealistic the MPG figures from the computer are, my last tank the computer said 58.9 mpg since refuel while the calculated average from Fuelly is 52.51! Is the trip computer getting even more inaccurate?

As a corollary to that, the 'range to empty' and fuel low warning lights are wrong too. At the last fill the fuel warning light had just come on and range was predicting 55 miles, but the tank only took 42.6 litres. This means there was at least 7.4 litres left in the tank so at my true mpg figure I had 85 miles left but on the computer's mpg figure it should have calculated I had 95 miles left!

Something is not quite right with the trip computer, shame really as if it was accurate it would be really useful!

Mine tested against fill up to fill up is only about 0.5 MPG out, and thats over 4600 miles. Yours sounds like it's got a problem.

 

[Julian1977]

At the last fill the fuel warning light had just come on and range was predicting 55 miles, but the tank only took 42.6 litres.

The range depends on the driving still on that particular moment, I think.

After few miles of enjoying myself I had a range of 310 miles. 10 miles later of driving sensibly I had a range of 325 miles!

 

[DEAN0]

So just to add a bit more evidence to how unrealistic the MPG figures from the computer are, my last tank the computer said 58.9 mpg since refuel while the calculated average from Fuelly is 52.51! Is the trip computer getting even more inaccurate?

As a corollary to that, the 'range to empty' and fuel low warning lights are wrong too. At the last fill the fuel warning light had just come on and range was predicting 55 miles, but the tank only took 42.6 litres. This means there was at least 7.4 litres left in the tank so at my true mpg figure I had 85 miles left but on the computer's mpg figure it should have calculated I had 95 miles left!

Something is not quite right with the trip computer, shame really as if it was accurate it would be really useful!

If you are convinced your calcs are good then get someone with VCDS to add the correction factor to the system ( it is an available option )

Your numbers suggest a 12% error - any chance you have a DTUK box fitted ? - they seem to screw up the computer by about 12%

 

[Havsgaard]

I'm driving a 2.0 150, and the DTUK box seems to screw up the figures a bit. In my experience especially map 2 and 3, but I'm only using Map1. It is ok quite accurate on map 1 - don't know why, but when calculating after filling the tank, it is very close to what the computer states - +/- 1.5mpg - so not bothered by that small bit.

In total during the past ~57.000 km(35418.16 miles), I have gotten around 22 km/l 62mpg and yes, I note it each time I'm doing a refill, and I am using the total amount of km on the main dash - not the computer.

During winter, there's a great impact of mpg vs summer - I see deviations of up to 15% comparing the max and minimum end-points (worst case is ~55.9mpg and best is ~67,2mpg)
The medium is around 62mpg (100%) but mostly winter mpg is around 95% (59mpg) and summer is 105% (65 mpg) - so the trend here is +/- 5%.

 

[Luckypants]

If you are convinced your calcs are good then get someone with VCDS to add the correction factor to the system ( it is an available option )

Your numbers suggest a 12% error - any chance you have a DTUK box fitted ? - they seem to screw up the computer by about 12%

Might need to do that. Another thing to add to the list of things I want doing via VCDS.

I don't have DTUK box, it's a company car.

 

[Julian1977]

I refuelled today. Just over 44 litres (that's 9.7 gallons) went in and I covered 498 miles since the last refuelling. The computer showed exactly 51 mpg. 498 divided by 9.7 is 51.3. The fuel tank was not 100% full. This makes the computer quite accurate.