[Matteo567]

I have a feeling that the only possible answer to this conundrum is that the trip computer is unreliable - there seems to be a few posts about that here.  Anyway, the situation is:

I regularly "fill up" (note inverted commas) with 42/43 litres of diesel when the DTE falls below 50km.

The other day I did this and noticed (as usual) that the DTE showed 760km.  For some reason I suddenly recalled that a few years ago this would show around 820km.  This got me thinking that something was wrong and so I kept an eye on the fuel economy and discovered that it always read 5.7l/100km.  That works out at approx. 43 litres and so I wasn't so concerned.  But the "820km" still niggled me and I checked the manual to find that the tank held 53 litres. 

That get me wondering why I could only get 43 litres in the tank before the pump kept cutting out.  Either the DTE reading when I filled up (i.e. around 50km) was way out or I could actually get another 8 litres or so fuel in.  Obviously if there was actually 53 litres of fuel in the tank and I was getting 760km that made for lousy fuel consumption (about 7l/100km).  Yet the computer read 5.7.

So, this morning I got fuel with the DTE showing 72km - which at 5.7l/100km my rough mental arithmetic figured there about 3 litres in the tank (note: actually, it should mean 4 litres).  Based on this I kept the fuel running, ignoring the cut out, and managed to get exactly 50 litres in (i.e. what I thought was a full tank).

When I got in the car, the DTE showed only 772km(!) - and counted down during my trip (with no apparent correction).  And the economy still read 5.7.

What is going on?

For reference; my trips without stopping are predominantly within 60km and as it's mostly country roads I'm rarely going above 70kph. At the moment the temperature over here is around -5C°.  Since the 50 litres only cost me €45 I suppose I shouldn't be too bothered but it's bugging me.

[AlanHo]

The DTE is a crude calculation based upon how much fuel is in the tank and your recent fuel economy.


If you have not reset the economy trip to zero for a long time - it would take many miles of driving at a lower or higher economy figure before the average changed.


My guess is your recent economy has been worse that the 5.7 which has caused the DTE to hover at a lower figure.

[Asterix]

Hmm, you're not alone in not understanding the DTE.. 

I allways zero the trip computer at every fill up, and I always brim it. I often get around 1000 km before refueling but anyway the DTE only shows 750-850 after fill up.... 

[tohis]

The fuel level sensor may not notice the very last liter or two which you can squeeze in when brimming it carefully. Also, the ground next to the pump may be inclined sideways, which will affect how easy it is to brim. There are many things which make it quite impossible to have very accurate DTE. It may do some learning about your driving habits, which could explain different DTE readings after filling it up.

The best advice about DTE is, don't trust them, and go refueling when there's still more than fumes left in the tank. 

[Dazzler]

The DTE in most cars I have had, has been conservative. You can understand manufacturers programing it this way, the same as making their speedometers over-read. 

[Phil №❶]

The DTE is most likely programmed to stop calculating @ about 50 litres, regardless of what is actually put in the tank. You must reset your trip computer before filling. When reset and set to display l/100k your should get ridiculous readings for the first 30 seconds, then it should settle down gradually, as distance traveled increases.

Hy actually don't advise brimming the tank as overflow can be hazardous and dangerous under certain conditions, however, many owners on this site (including me), brim their car's tanks every time.

[XinZhao]

My experience (2011.FD with dpf) is that i always remember it shows 907 km left after full tank.
I brimed it a few times and it also saod 907.

So i guess ECU can't register the fuel above certain level.
I don't brim any more (and i am sad because of it) because I read that it shoud not be done that the apace is reseved for the fuel fumes.. Also there has to be place for expanding the fuel due to warming up.
But if anyone can confirm that briming has nobjegative effect if I brim it only before a long trip, it would be great to hear it.

Not so long ago, after refueling I noticed DTE shows only (I think) 878 km left.
 
My consumption is around 5.5 l/100km and I noticed an increase of about .5 - my rear left brake was stuck, got it repaired and it got back to normal.

Or should I say "normal"?! Because, my consumption was earlier about 5 or even less so i think my front brakes are a little stuck too.
When measuring the temperature of the front break disk after longer driving (and only small amount of breaking to stop it) it shows temperature of about 25 C. Ambient temperature 0C (32F).

So, I don't know if it is normal or should it be colder?

[Dazzler]

@XinZhao

Many of our Members brim their Diesel i30s and none of them have ever reported any adverse side effects of doing so. You should certainly be safe to do it if you are doing a reasonable long drive immediately. 

[Phil №❶]

 

[tohis]

Once I tried to brim to the last drop, and noticed a puddle of fuel behind the wheel, and that breather hole under the filling hole also spat some fuel out. So, after the first click of the filling pistol, I just add slowly a liter or two more and then stop to prevent overfilling. It's no big deal to go filling a bit more often. 

[Doggie 1]

I allways zero the trip computer at every fill up, and I always brim it. I often get around 1000 km before refueling but anyway the DTE only shows 750-850 after fill up.... 

Same here.
And at @ 43 litres the bowser cuts off too when refuelling but I usually feed about another ten litres in to brim it.

[Matteo567]

Thanks for the replies - it does seem that the DTE calculator is out.  I zeroed the trip and fuel economy that evening (after posting here) and already, after a few days driving, the trip v DTE is out - i.e. if I add the trip to the current DTE I get a larger figure then the DTE after filling up.  Though I should still be getting a much higher figure.

I'm going to keep a close eye on things and see how it turns out.

Interesting what Doggie 1 says about the fuel cut out at 43l. 

I'm pretty confident that filling the tank to capacity (i.e. 53l) can't be wrong - though I can see that putting in more (so it's in the feeder pipe??) could be dangerous - and I suppose in any case there is a safety margin built in to allow for a litre or so more than 53.

[Doggie 1]

Thanks for the replies - it does seem that the DTE calculator is out.  I zeroed the trip and fuel economy that evening (after posting here) and already, after a few days driving, the trip v DTE is out - i.e. if I add the trip to the current DTE I get a larger figure then the DTE after filling up.  Though I should still be getting a much higher figure.

I'm going to keep a close eye on things and see how it turns out.

Interesting what Doggie 1 says about the fuel cut out at 43l. 

I'm pretty confident that filling the tank to capacity (i.e. 53l) can't be wrong - though I can see that putting in more (so it's in the feeder pipe??) could be dangerous - and I suppose in any case there is a safety margin built in to allow for a litre or so more than 53.

I may stand corrected, but I think the GD has a 50 litre tank (with the non IRS) and I have had 53 and 54 litres in it.
That does include the filler pipe but I always drive it straight away so I don't see a problem. I've always done it this way with both i30s.
In my last (FD) diesel. I regularly put in 60+ litres. It was definitely a bigger tank (quoted at 53 I think).

[Matteo567]

Just a quick update, one week after the post.

So, to recall, I put in 50 litres at DTE 72km and got a DTE of 772 (and an economy of 5.7l/100km).

Today it's showing a trip of 753km with a DTE of 105 (and 5.6l/100km).  Somehow I've "gained" 86km.  I think...(it's been a long week  ).

[Asterix]

Just a quick update, one week after the post.

So, to recall, I put in 50 litres at DTE 72km and got a DTE of 772 (and an economy of 5.7l/100km).

Today it's showing a trip of 753km with a DTE of 105 (and 5.6l/100km).  Somehow I've "gained" 86km.  I think...(it's been a long week  ).

Nothing unusual in that ... 

[Phil №❶]

Yes, it has more information than it did at fill up about your fuel consumption, pertaining to the current fuel used.

[Matteo567]

OK, so I filled up (with 50l) the day after my last post with a DTE of less than 50km and a trip of 828.  The DTE after fill-up showed 763.  Now we know that this is unreliable but will someone out there "riddle me this" because I'm completely bewildered, bamboozled, flummoxed and any other word the thesaurus can bring up:

This morning I squeezed in 50l (the fuel pump was again continuously cutting off after 43l) with a DTE reading of 72km and a trip reading of 817km - so I would have managed a shade under 900km on 50l since my last fill up.

I got back in the car, zeroed the trip and the fuel economy (5.7l/100km) and read off the new DTE...wait for it...606km   I checked the ticket (it said 50l).  I checked there wasn't a pool of diesel outside the car (there wasn't).  And I checked the fuel gauge (absolutely full).

I then did the school run and after 33km the DTE was showing 572km (economy 5.8l/100km).

A (virtual) cigar for anyone who offers the best explanation.

[liability]

A (virtual) cigar for anyone who offers the best explanation.

Greenhouse effect?

I have only had my diesel i30 for 2 months, but I agree that the DTE and in some cases the litre/100km readings have no relation to reality.

I have noticed, though, that if I fill my car until the pump cuts out I can usually fit in another 10 litres if I spend a few minutes dribbling it in. This will surely have some affect on DTE?

[AlanHo]

I don't know about Belgium - but its been freezing cold in the UK recently and the fuel economy of my car has taken a hit. First because it's so cold and second because my wife has used the car most days for short shopping etc journeys.

The effect of this is that when I filled my car up a couple of days ago the DTE was much lower than "normal". This underlines my theory that the DTE uses your recent average economy and the fuel level in the tank to calculate the DTE.

I'm not surprised that your DTE should drop - but I confess it seems a rather unusual amount.

I too have been curious about the DTE and range forecasts and have been keeping a record of the figures for each graduation on the fuel gauge.

This is the result - but note that my car is auto petrol and not diesel and the figures are in miles.


You will see on the most recent tanks - the DTE and range has dropped considerably - cold weather and short trips are the probable culprits. The first tank was in October when the weather was warm.

[xiziz]

Many odd things. Mine seems quite accurate, .1l margin on the consumption compared to measuring at the pump, probably due to rounding. The remaining distance is not quite as accurate, it falls slower than real distance travled, usually says 850-900 after filling, usually go just under 1k km per tank. Usually get 49l in, to the first click, never bothered brimming, seems to take the ammount it should, manual says 53l.

Weird that it shuts of at 42l for many of you, I fill at a fairly modern Statoil pump though, could it be older pumps that shut you out earlier?

[eye30]

I'm sure mine actually went up.

 i filled up, checked the reading then did a trip.

 on checking after the trip the read out was more than i expected

i.e. dte less travelled = x but the readout was x+?

[Phil №❶]

I'm sure mine actually went up.

 i filled up, checked the reading then did a trip.

 on checking after the trip the read out was more than i expected

i.e. dte less travelled = x but the readout was x+?

So if you trusted the readout, would you have been left stranded ?

[eye30]

I'm sure mine actually went up.

 i filled up, checked the reading then did a trip.

 on checking after the trip the read out was more than i expected

i.e. dte less travelled = x but the readout was x+?

So if you trusted the readout, would you have been left stranded ?

I think it calculates based on your driving style and the ecu does a recalculation

[Matteo567]

Well I'm also assuming that the calculation is makes is based on driving style and that's why I'm so confused about the DTE 606km reading.

When I filled up I had a DTE of 72km and a fuel consumption of 5.7 (I'd noticed since the last fill-up that this had fluctuated from 5.6 - 5.8 so not so much).  Based on those figures I calculated there was approximately 4 litres left in the tank.  I "brimmed" it to exactly 50 litres (simply because that was the amount I put in the last two times since I've been paying closer attention to the consumption) giving me 54 litres.

Now, at an average consumption of 5.7 I should get a DTE of 947km.

I know the DTE is unreliable and after fill-up gives a lower reading but how the hell did it come up with a mere 606km??  That either means the computer is working on a consumption of 9l/100km or a tank with only 34.5l of fuel. 

As an update: after this morning's drive, the readout was TRIP: 139, DTE: 462, consumption 6.0l/100km (it was very cold) - so it still has not corrected itself.  By the way, the needle of the fuel gauge is on the "full" line - after fill-up it was slightly over).

Could it possibly be down the fact that I zeroed the consumption and trips readings before checking the new DTE??  That surely can't be right as that's just the display; the computer knows what the figures are. 

Very strange...

[Dazzler]

Never very accurate, but not usually out anything like that amount. Be interesting to see what would happen if you reset everything by disconnecting -tive terminal of battery for minimum of 30 minutes. ..

[FatBoy]

It doesn't calculate your DTE on your last fill, but on your most recent driving history (think last ten minutes, not last fill), and recalculates accordingly.  For example, if you have been driving in the city for the last 30 minutes prior to your refill, then the DTE will be low.  Drive on the highway for a bit after that and the DTE will increase.  Conversely, if you fill on the highway then the DTE will be high, start driving in the city and it will come down dramatically. 

It shows you when it expects you to run out of fuel with your current driving, not the current tank of fuel.  That is why it is always changing.

[Matteo567]

Hmm...I'll buy that - it makes sense.  But it doesn't make sense for my weird DTE figure when I last filled up.

The consumption rating was 5.7/100km and I had at least 54 in the tank - that should give a DTE of 947 - not 606.

Anyway, an update below will show that it's correcting itself:

15/2 (fill-up)
DTE: 606
L/100km: 5.7

16/2
Trip: 139.1
DTE: 462
Range: 601
L/100km: 6.0

17/2
Trip: 233.5
DTE: 394
Range: 627.5
L/100km: 6.0

18/2
Trip: 349
DTE: 334
Range: 683
L/100km: 6.0

19/2
Trip: 444.2
DTE: 284
Range: 728 (fuel gauge was showing between half and 3/4)
L/100km: 6.0

22/2 (sorry - missed the weekend readings)
Trip: 610.6
DTE: 201
Range: 811.6 (fuel gauge showing just left of half)
L/100km: 5.9

23/2 (this morning)
Trip: 721.5
DTE: 146
Range: 867.5 (fuel gauge reading 1/4 - which seems a big drop...)
L/100km: 5.9

I put the fuel gauge readings in above to give some sort of indication as to how much fuel there actually is.  But...if I have 1/4 tank, and assuming the gauge reads off the official 53 litre capacity, I should have approx. 13 litres left.  If I take the higher 6.0 reading for my recent fuel consumption, I should have a range left of about 220km [so a total of about 940 - probably a bit more considering I had at least an extra litre in the tank.]

I'll keep you posted how it looks when I next fill up.

Or am stuck on the side of the road having run out of fuel ;-)

[FatBoy]

Try resetting your l/100km ten minutes before you fill up.  That should give you a better indication of what the DTE will read.  Not the l/100km since you last filled.  The DTE keeps recalculating, so you shouldn't run out of fuel if the DTE still says you have XXkm to go.  If I remember correctly, with my FD if it got below 50km remaining then it didn't show a distance, but flashed "--".  So I filled up then.

I think you might be overthinking how the DTE works.

[Matteo567]

Thanks Fatboy, but I saw it just too late - filled up this morning.  Will try that next time (though not sure why it would work).

Anyway, the conclusion...or is it? (cue clap of thunder and flash of lightening):

24/2
Trip: 812
DTE: 98
Range: 900
L/100km: 5.9

25/2 (at fill-up)
Trip: 912.7
DTE: <50
Range: *
L/100km: 5.9

* at 50 the trip read 899, when it clicked to "- - -" it read 901.  Now I've always assumed it changes to "- - -" when it calculates it should be 49; it makes sense it would do this at 1km below the lowest reading.  And yet, it did so after I'd driven 2km.  So, the ultimate range must have been between 949 and 999.  I didn't want to chance this theory (and in any case my wife would be driving the car next, would almost certainly fill up, and I wanted to keep a record), so I filled up with a DTE of what I assume was either 36 or 72.

This time I managed to squeeze in 55 litres (at 94€c - damn it's nice to see the litres go up quicker than the €s) and got back in the car, started her up, and the DTE read...

642!

It's due for its 130k service so it will be interesting to see if this makes a difference to the fuel consumption (obviously not this weird DTE thing - not a clue what's going on there!)

[FatBoy]

Where do you fill up your car?  Is it in the city, the suburbs or on the highway?  Do you drive there straight from home or work (ie. engine isn't at operating temperature)?  The most recent driving history will have an effect on what your DTE reads when you fill up.  If you reset your trip computer just prior to fill up you may find that your economy is closer to 10 l/100km than it is to 5 l/100km.  Hence it will only think that you can get approx 600 km from a tank.

As for fitting in more fuel and not noticing any change.  Your fuel gauge still reads full, so the DTE is calculated on a "full" tank, regardless of how much above "full" you have put in.

Don't over think it.  It won't let you run out of fuel unless you try and cheat the system.  When it starts flashing "--" don't try and drive 72 km.  You may get there, but the trip computer thinks otherwise "ON YOUR CURRENT DRIVING HISTORY".