Outline · [ Standard ] · Linear+ Average fuel consumption

Hi guys I've been thinking, according to user manual, average fuel consumption is too high, and I've some doubts about that. Mine average consumption (mostly open road, some in the city) is between 6 and 6,5 l of unleaded gasoline for 1.6 MPI engine, which is less then factory stated. For example, on open road, with speed of 100-105 km/h fuel consumption is about 5.5 l/100 km.......mine old diesel doesn't have such low consumption. There is short video clip I recorded to demonstrate this phenomenon. I'm sure board computer doesn't lie What is your expirience? This post has been edited by Keka: 9 Apr 2008, 00:27

Hi guys

I've been thinking, according to user manual, average fuel consumption is too high, and I've some doubts about that.

Mine average consumption (mostly open road, some in the city) is between 6 and 6,5 l of unleaded gasoline for 1.6 MPI engine, which is less then factory stated.

For example, on open road, with speed of 100-105 km/h fuel consumption is about 5.5 l/100 km.......mine old diesel doesn't have such low consumption. There is short video clip I recorded to demonstrate this phenomenon. I'm sure board computer doesn't lie


What is your expirience?

This post has been edited by Keka: 9 Apr 2008, 00:27

90% city, 10% outside, 1.4MPI:
in winter - a little over 9 liters/100 km
now - around 8.5 k/100 km
summer - I don't know, my Logan is only 6 months old.

All within specs.

This post has been edited by stajp: 9 Apr 2008, 00:30

I'm sure board computer doesn't lie 

An extended topic on romanian section concluded: the computer does lie.
The average consumption is like factory stated or even a little bit high.

Mine does not
When I go to gas station, consumed fuel on board computer and quantity of fuel I add for full gas tank corelates +- 1l !
I still think mine car uses less fuel than stated in factory

My 14mpi uses by normal driving 7,4 per 100km
Stu

As I promised, I kept an extensive statistics on fuel consumption almost from the first day of owning a Logan, and up to date it shows the following:
- average consumption in the city varies from 9.4 l/100km (in the summer) to 11.8 (in the winter), with an average of around 10.5 l/100km at an average speed of about 22 km/h, which is a lot above factory specs, but I explained that in my other posts, it is a result of mostly short distances (less then 3 km per drive).
- average consumption on the motorways (but with crossing of high mountain passes, 1000 m and higher) was 6.4 l/100km, at an average speed of around 60 km/h.
- average consumption on the highways and motorways (2/3 highways and 1/3 motorways) at an average speed of nearly 90 km/h (120 km/h on the highways, and maybe 50 on the motorways) was 6.9 l/100km. Those results are well within the specs.

I was also interested in finding out if the board computer lies, so I also kept a record of a difference between consumption in liters indicated by the board computer, and liters measured on gas station pumps. The results are interesting - while the total average error is around -2.5% (sign "-" meaning BC shows less then measured by the gas station), deviations per single filling range from as low as 0.7% to as high as -20.5% and +9.4%!!!

But, all in all, I still believe that measurement by the BC is more accurate, because Renault/Dacia has less interest to measure it wrongly then the gas stations, which turn their "error" into money.

This post has been edited by g100sic: 9 Apr 2008, 23:50

OK, my average LPG consumption is: city short relations - 11.5 (l/100km), open road 90km/h - 5.7, 120km/h - 7, 160km/h - 10, 180km/h 12.5. City in winter time (with a lot of defrosting) - up to 15l.
Another thing about BC and fuel consumption measurement. There is no flow meters for either gasoline or LPG flow measurement, but instead, the system only evaluates fuel consumption by measuring AIR FLOW to the engine, so all the displayed quantities are approximation and can not be fully trusted. My experience is that it measures from the exact to +30% compared to the fuel station measurement (depend of the season, driving style and of course how hard you push the gas pedal). I have a friend working at the LPG station who told me that the pumps are inspected and calibrated by the authorized (state) personnel very often. Since I doubted it, he invited me once to see what they were doing, and from that moment on I don't trust my BC over their measuring.
Few weeks ago I went to a regular (10000km) LPG system service. They checked and readjusted the mixture parameters (by comparing system response to the lambda sensor signal working on gasoline/LPG), and after that BC shows more reliable values (coincide with the LPG station measurements).
Greetings to all the members, specially to Stu.

@Loganovac
What you say may be a method for measuring fuel consumption in Logan, but if this is truth, and that is the only method, that does not explain one other thing. When you enter a service mode on the dashboard display, one of the data that can be seen in service mode is how much fuel is contained in the tank! And that changes not only by the consumption, but also when the fuel is filled in the tank, which doesn't have anything to do with the consumption, and which means that it is actually measured! And with the injection engines there is a much better way to measure the fuel flow then by measuring air flow. Injectors are effectively miniature volumetric pumps with known volume, so the number of it's cycles can be easily converted into fuel flow.

Regarding strange deviations of measurement by the BC and gas station pumps, in order for both measurements to be consistent, it would be necessary to fill the tank to exactly the same level every single time, which is virtually impossible! The biggest difference in my statistics was 6 liters, while the average difference is less then 1 liter.

And, regarding the pump calibration, first of all, as any other measurement instrument they are not absolutely precise, and so they have it's so called error class. If for example pump's error class is 3%, it is still within the legal specs for the inspection and calibration purposes if its measurement error is, say, -2.9%. Secondly, density/volume of the petrol is highly temperature dependent, and that affects the measurement by the volumetric pumps if they don't have integrated some method of calculation compensation.

This post has been edited by g100sic: 13 Apr 2008, 20:06

Although I have also studied Metrology on my College, I think that just by taking the challenge we would go completely off topic. Anyway, you are right about a lot of things. But what is 3% pump's error class compared to an average of 17.6 % BC readout discrepancy on a 12 consecutive tank fillings (first few months I was keeping records of all the filling quantities and km readouts). I am talking LPG. And on the gasoline, how well known do you think is the volume of the injector pumps? Don't you think it does not depend of the fuel density/temperature, fuel pressure, time and pump's mechanical system uncertainty? Other than that, have you ever seen what is measuring fuel quantity inside the tank? There is a float connected to a potentiometer ! How precise do you think it is having in mind also the shape of the tank (big area, shaped bottom, low hight)? BC's fuel consumption calculation has nothing to do with it, but the estimation of the km's available with the rest of the fuel in the tank relies of that as well as the displayed fuel quantity in the tank (by bar graph, very coarse). I would be very pleased if my BC is 100% precise (OK, with a few percent error class), but.....

Currently, I have in my table 18 consecutive readouts. Of those 18, 9 are within 3% difference, 3 more within 5%, further 4 within 10%, and just 2 readouts have an extreme discrepancy of more then 10%, and I believe that is mostly a result of how the gas station staff interprets your "fill it up" order. Or, if you want it in liters, out of 18 readouts, 7 were within 1 liter, further 3 just above 1 liter, 1 more under 2 liters, another 3 readouts under 3 liters of discrepancy, and 3 above 3 liters with the highest around 6 liters.

Interesting thing about your readouts is that your BC started showing more reliable results AFTER you had your LPG system checked and READJUSTED! Lets not forget also that LPG and petrol have quite different characteristics, which might "confuse" the measurement system.

Regarding outside conditions, you are right that there are variations as well as at the gas station. But, I believe that they are actually much better defined in the vicinity of a warm engine. As for the volume of the injectors, there is actually no need to know it exactly, as it is just enough to average it empirically through a series of calibration measurements. I certainly don't expect that every single Logan produced has a custom calibrated fuel flow measurement...

And yes, I have seen how the fuel level in the tank is measured in my old Lada Samara, and indeed it is measured just the way you say. But I can't say that I have seen how it is measured in Logan, so you got me there . What I do know, in service mode, the level (the quantity of the fuel, that is) in the tank is not displayed by the bar graph as in regular mode, but numerically, in liters! I don't know how precise it is, but there is an idea to check that too ! So, next time I go to the station I will note the quantity in the service mode before and after the filling, and compare that to the measurement by the station pump, and report here, of course.

<span class='edit'>13 Apr 2008, 22:46:</span>
There is an interesting document for those who want a more detailed insight in how the fuel supply (among other things) works in Logan, just google a bit for a "MR388LOGAN1.pdf"!

In fact, a single constant-pressure fuel pump is actually integrated into the "pump-gauge-filter" assembly fitted in the fuel tank itself, and a fuel system does not have a return line as in conventional (non-injection) system.

The air intake also has a temperature sensor which is used for adjustment of fuel flow according to the outside temperature (automatic cold start). So, the injection computer ("SIEMENS-SIRIUS 32") has all the necessary data for a reasonably correct measurement of the fuel flow. Indeed, it has to, in order to achieve fine tuning of fuel mixture needed to satisfy the EURO-4 standards.

This post has been edited by g100sic: 13 Apr 2008, 23:46

If you like, you can find also the picture of the fuel float-meter in one of the MR388LOGAN documents. Peace?

"Peace?"
And who was fighting ?!? Did I miss something?!
But if it's for the sake of having a beer, then OK

Seriously, though, I said you got me on fuel float-meter. It is a simple and cheap method of conversion, so why would anyone even bother trying to find something else. But it still gives only a raw analog signal, and when you have a computer at hand you can do a lot of usefull tweaking with it, which was not possible back in the old Lada Samara days...

My urban consumpion measured between multiple pomp filligs is 8.5 - 9% on a distance of around 900 km. The urban consumpoin is more than OK, but on the open road I can't get the value from the book, probabily because I can't stand to see the clock showing only 100km/h .

This post has been edited by FILter: 16 Apr 2008, 13:43

my onboard computer shows about 8.8 - 9.8% at ~800 km at normal usage in the city, depending on the season. but i have never made a "classic" test yet(im too afraid of the results ). i have made only an "economical" test and i managed to get 6.5% in the city, but only when i used to make night shifts sothere was no traffic

This weekend I went for a ride from Zagreb to Istra (I'm in Croatia). 400 km round trip (200 there, and 200 back) on highway and fast motorway + 50 km around Istra on small local road. Average speed 75km/h (although, on motorways I was always aroung 110-120, tractors in Istra so slooooooow) , 450km, average consumption 6.3l/100km.

I fueled up before the trip, and on BC it said I used 48.3L, and I tanked 48.2L. In the last 6 months BC was never wrong more than 0.5L.

7500 km, mostly on moderate city traffic, on-board computer indicates an average of 7.4l / 100 km. I never drive the car for less than twenty minutes, once started, and traffic deadlocks are scarce here. The average speed is about 35 km/h.

This post has been edited by hash: 21 Apr 2008, 13:38

you should stay a week in Bucharest

today, after 20 km my average speed is 10

This post has been edited by ga!nusha: 21 Apr 2008, 14:48

After the last filling:
- gas pump measurement: 41.3l
- BC measurement: 40.2l
- tank measurement in service mode: before the filling 8 l, after the filling 50l, difference 42l

So, discrepancy between BC and gas pump -1.1l or -2.74%, and discrepancy between tank and gas pump +0.7l, or +1.67%.

Average (real) consumption and speed (completely in the city) were 10.5 l/100km and 22.2 km/h respectively, for an average daily distance of 8.9 km covered in 24 minutes.

Four consecutive LPG tank filling (after the LPG mixture readjustment mentioned in my topic #7) - 10.8 l/100km all urban driving (heavy foot), board is unexpectedly accurate (approx. -2 lit. comparing to LPG station measurement of an average 37.5 lit. refueling quantity each, always on the same LPG station - I suppose this is the quantity of a gasoline that I used while warming-up the engine). Without any doubt, they did the right thing, now I am sure the the mixture is ideally set for the LPG, exactly the same as for the gasoline! Miraculous!

finally, I've got my Logan 1.4MPI. After first 100km in Logan's life, in typical city conditions of driving, fuel consumption is about 15L ?!?!?!
I am dissapointed

what is amount of fuel in tank when "reserve" light gets on?

Peja

Just wait few hundred of km more. Then your mileage will be settled down. Try the "full tank-to-full tank" method and see the results. Till then... chill out.
Success!

what is amount of fuel in tank when "reserve" light gets on?

Peja

about 5 liters

about 5 liters

is it dangerous for fuel pump, if driving with "reserve" light turned on?

peja, how would the fuel pump know the light is on?

seriously: specially on diesel cars it might not be advisable to
use the very last liter of any tank - it might over the time have
accumulated dirt and sand, and although this then might not
directly harm anything, it will clogg up filters before and after
the pump, and in an extreme (very seldom) stop the car.

so depending where you are, how old the car is, and how 'dirty'
the gas stations might be, avoid the very ( ! ) last liter.

the light comes on at slightly over 6 l, not 5 as mentioned at times.

and just in case you really run out and get stopped by using the
very last drop of your tank: after refilling, be it by a spare tank or
at a station, wait well over a minute for dirt then stirred up in the
tank to settle down before you start the engine again.

and: unless you drive through the blocked traffic of belgrades bridges
every day, in and out and in and out, averaging 15km/hr, there is NO
dacia that uses 15l/100km, ever. so dont worry, you just made a
calculation mistake.

pls, read the other post here about max fuel tank capacity for some
further info.

greetings - heinz -

This post has been edited by heinz57g: 27 Jun 2008, 17:58

peja, how would the fuel pump know the light is on?

wait well over a minute for dirt then stirred up in the
tank to settle down before you start the engine again.


pls, read the other post here about max fuel tank capacity for some
further info.

greetings      - heinz -

HEY !!!
If I wait till the dirt settles it settles to the bottom of the tank and the fuel is extracted from the bottom of the Tank

Stu

thought you would catch me there, but only almost: as long as we are not talking
about tons of sand, there is still a dip, some 5mm and circular, around the actual
fuel outlet going to the pump, and that dip takes enough of the sand and sludge.
same on almost any car, have a look if you get a chance.

fact is also that most of the western gas stations, and many of the newer ones in
the balkans, are so well filtered, that sand and debris are rare at most.

water in tanks though is still common in older rural stations in greece. great fun
when you drive a diesel ...

greetings - heinz -

On some Serbian Dacia forum, it was said that cause of heating of fuel pupm, it is denagerous of driving on minimum. As they stated, fuel pump is cooled via fuel in reservoar...

I've started new measurement. When "reserve" light turned on, I've added 30L, and I'll see how much it will run till next "reserve light".

>> fuel pump is cooled via fuel in reservoar...

nonsense. sure, a fuel pump could run dry (and hot) when totally empty, but how long will you have it switched
on when the engine is not running anyhow? seconds?

>> I've added 30L

first the light will come on, then the BC will go off, within minutes of each other. unless you do only city driving,
30L should last you 360-430 km.

where are you in SR, and what roads do you drive on average?

greetings - heinz -

This post has been edited by heinz57g: 28 Jun 2008, 20:03

I don't have BC, so it is hard to know what is average speed, but I think it is 20-25km/h (Max 45km/h + crossroad signalisation stops) on rout of about 6km.

I live in Nish, so routs are small with lot of crossroads

Nis is a tough one. not really totaly bugged like belgrade at times (my record is
airport to citycenter 25 km in 1h:24m), but still slow during peak times. and
plenty of road constructions, traffic lights.

i would guess 10l/100k should come out as a long time average, unless you
do some long out of the city drives, and it will sink to below 8.

do not overvalue one really bad days (yes, you might reach 15 then), it will
sink on average.

talk to g100sic, he should know, living in a similar city, but doing rather little
driving in-city only.

actually, we used the motel nais to end of the highway at leskovac trip (130km
return) once for fuel measurements, as closely and carefully as we could topping
up and driving with 125kmh on the clock, and came to 6.72 (just before stu will
jump in and ask, we did not do this for fun only, but had to pick up somebody
at the leskovac end - so it came in handy.)

this part of the highway is not really even, the hills fool you, but it should average
out going-coming.

please also do not underestimate, that YOU will get used to your car after a while,
too, and that that will greatly influence fuel consumption also. more then one tends
to admit.

greetings - heinz -

This post has been edited by heinz57g: 29 Jun 2008, 13:00

PLEASE DO NOT POST OFFTOPIC MESSAGESS!!!