4x4 tank shape

[LetoThe2nd]

Hi!

Still having problems with my tank capacity in my 4x4 (it should be 60l, but its effective 52-53).

One of the mechanics at the dealers said that the tank bottom in the 4x4 is shaped in W shape (the rear drive being in the middle), and the both halfs bottoms being connected in some way.

Does anyone have any idea if this is true, and what kind of connection it is (just a pipe using gravity and liquid pressure, or a pump).

My symptoms would be consistent with the connection not working (or blocked).

From the time my fuel warning light comes on, to the time I really must fill up (the computer saying I have fuel for 20km) I only use up about 3l of diesel (according to the computer) - so I'd say only 1/2 of the reserve is available to me (and the same for about 10 % of the tank before the reserve - the km till fill up behave normally till about 1/4 of the tank, and then fall rapidly).

Cheers,

Leto

[skomaz]

Yep as far as I know it is a saddle tank (W shape) so must be connected although not sure how.

I was under the impression though that it had twin fuel pumps - once for each side?

[LetoThe2nd]

Tnx,

So I'll have to make the dealer check if both pumps are functional...

Anyone knows if they have separate wiring (if not any suggestion how to check?)

Leto

[EddyH]

There's only one pump as standard not two. The problem sounds like the pump as it's this that moves the fuel between the two tanks.

[No Waiting]

When I fill mine up I fill it to the brim and then rock the car (via roof rail) - loads of air bubbles up then I can get aload more in - no idea how much as I've never looked at the pump readings.

[London Les]

A good reference shows the tank is indeed a saddle-tank arrangement.

The sides are linked by two pipes that draw fuel from one side (which has the level sender) to the other which has the main fuel pump.

The reference states that if the engine runs short of fuel, but the fuel gauge shows 1/4 full, then the transfer pipe should be checked as it may be blocked.

Hope that helps.

[LetoThe2nd]

A good reference shows the tank is indeed a saddle-tank arrangement.

The sides are linked by two pipes that draw fuel from one side (which has the level sender) to the other which has the main fuel pump.

The reference states that if the engine runs short of fuel, but the fuel gauge shows 1/4 full, then the transfer pipe should be checked as it may be blocked.

Hope that helps.

Is it possible, they changed that recently. My 4x4 (2007) behaves like it has the pipe blocked, but the level sender and the pump at the same side - like I said about the last 1/4 of the tank is used up in 1/2 of the time/distance (the reserve shows empty after 3-4l after it started).

Cheers, Leto

[London Les]

Yes - that's possible - the tech reference refers to a 'level sender 2' which is on the same side as the pump, but I don't understand the point of having two level senders, and which one is reported. Complicated things, cars!

[skomaz]

Could there b two level sensors to allow coordination of the pump drawing off from both sides, rather than having a simple gravity fed transfer?

Seems a bit OTT but possible.

[humsk]

... it should be 60l, but its effective 52-53 ....

How have you decided it's only 52-53 litres? I've ran mine until the gauge is on the empty bar, the trip computer says 0m range and then some more and still only got 58 litres in it. I take the fuel gauge and trip computer with a pinch of salt - they drop rapidly once I get passed half way. I work more on the trip meter - think about topping up after 550 miles.

[LetoThe2nd]

How have you decided it's only 52-53 litres? I've ran mine until the gauge is on the empty bar, the trip computer says 0m range and then some more and still only got 58 litres in it. I take the fuel gauge and trip computer with a pinch of salt - they drop rapidly once I get passed half way. I work more on the trip meter - think about topping up after 550 miles.

I know that the fuel gauge is pessimistic (in order not to run out of fuel), but the main problem is that my reserve lasts only half as long as it should. It should be 8l. If I reset the computer when the light goes on, and look at the data when it says its almost empty (10 km left according to the computer), use that data to calculate the fuel used I get to about 3l (it should be at least 6 or 7).

Furthermore, the km available always + km taken is always about the same for more than 3/4 of the tank and then drops rapidly (and I end up with almost 100 km less than it should be).

And finally the km available (till fillup is needed) drop with almost twice the speed in the final part of the tank (it drops 10km almost every 5 km or so, driving steady on a flat road).

I'll go talk to some other official dealers and see, if they are any better than the one I bought it from.....

Cheers, Leto

[skomaz]

So are we definite that the 4x4 has a 60 litre tank? The spec sheet in the brochure says 55 litre?

[humsk]

My owner's manual says 60 litres with a reserve of 8 but I don't know if that's 60 + 8 or if it's 52 (at which point the trip says zero range) + 8.

The dealer will probably say "they're all like that"

[LetoThe2nd]

my homologation card says 60l, and the spec I saw also said 60l for 4x4.

Cheers

[Niall]

My Mk1 diesel had a 55l tank and a 7l reserve.

I came to the conclusion that it was a 55l tank of which 7l was reserve. I once drove for 30-40 miles past "0" on the estimated range and was still only able to shoe horn 47l or thereabouts into the tank when I got to a petrol station. Add the reserve and you're just about back to 55l. I never had the guts to see how much further the extra 7l would get me!

On that basis; if it's a 60l tank of which 8l is reserve then there's nothing wrong with a 52-53l fill when the car says it's empty. Surely it's better to take the cars word for it and fill up when it says 0 range, rather than purposefully eat into the reserve and run the risk of having to call the AA or whatever when you're stranded for no good reason?

If anyone on here actually knows how the reserve works in relation to the tanks qouted capacity I'm all ears (especially if I'm wrong on how I think it works!).

Niall

[skomaz]

"the manual says..." Doh - yeah fogot to look in there!

I woud suggest that from experience of all the other cars I have owned the 60 will be 60 including reserve of eight so effectively 52 (which incidentally matches the positioning of the red sector in the gauge). Certainly the bong and the low fuel display in the maxidot seem to appear around the time the needle enters the red. And I would expect the trip computer to be conservative can you imagine the number of complaints the dealers would get if it as the other way round and people were running out of fuel when the computer said there was still some left?

[LetoThe2nd]

Why the ***** is everyone convincing me, that 52 L is normal....

1st of all if I fill up when the light turns on I get about 49l in the tank, if I fill it up when the computer and the fuel gauge says its empty it fills up with 52l

with 60l (including 8l reserve) the capacity should be about 50-51 when the light comes on (its close) and about 58-59 when the computer and the gauge say its empty (big difference here).... so effectively I have only a 3l reserve and not 8l (and that is not normal).

My car has a 60l tank and not a 55l one (according to the manual, the specifications in the brochure and the homologation card), so I should be able to put more than 52l in it, when the car says it empty. If I cannot, then something is wrong. I was asking for suggestions of what it could be wrong, and not to be convinced that its OK (or that I cannot read).

Leto

btw... the reserve should start when the light comes on (it was like that in every car I drove, the only difference was how was it marked - french cars have reserve start when gauge is at 0, german and co the tank is empty at 0 - including the reserve).

So as I said above, the light should turn on at about 51- 52l (not 49) and then I should have about 8l left in the tank (but I can use only 3)

[No Waiting]

1) Explain your concerns to the Dealer

2) Get the dealer to fully drain the tank

3) Poor a known amount of fuel into the tank (ie 5L)

4) Reset computer

5) Drive to nearest filling station

6) Fill tank

7) Work out fuel used to get to filling station (hence why the computer was reset)

8) You can now workout the actual tank capacity

9) Drive until the low fuel warning is displayed

10) Reset computer

11) Drive to nearest filling station

12) Fill tank

13) Again work out fuel used to get to filling station

14) Subtract No13 from No12 to get the amount of fuel added from when the low fuel warning came on.

15) Subtract No14 from No8 to get the amount of fuel left in the tank when the low fuel warning came on.

QED

[Niall]

Why the ***** is everyone convincing me, that 52 L is normal....

Because it is?!

What I'm suggesting is that the reserve doesn't start being "used" until your range is at 0 and the fuel guage says that the tank is empty. My Scout will need filled from nigh on empty in the next few days, I'll tell you how many litres it takes.

My Mk1 Octy didn't have a saddle tank and it too ran to "empty" at a capacity equal to the total tank capacity less the reserve figure.

Otherwise - run your car till it stops and let us know how many extra miles you get after the fuel gauge bottoms out and the range says 0 - and whether you can fit 60l in then!

Niall

[LetoThe2nd]

Hi!

If I translate what it says in my manual:

"The fuel tank volume is approx. 55l (60l in 4x4 vehicles). When the fuel gauge reaches the reserve marker, the dashboard display shows the warning fuel pump symbol. The tank contains at this point approximately 8l of fuel.

Maxidot display shows the warning 'Please Refuel', and a warning sound is heard'"

.... so when the warning light is turned on... there should be 8l of fuel left (about 52 liters of air in the tank).... I can put in about 49 l, and the main point is .... my useful reserve is not 8l, but about 4l.

So unless my manual is completely wrong, the reserve does not start when the fuel gauge says empty, but when it reaches the red line.

Cheers, Leto

[Niall]

I've now had two fills to check that my saddle tank is performing similarly to Leto's.

I think it is.

Filled up last week when the needle was between the last white mark and the first red mark on the fuel guage (just under 1/8th of a tank?) - just over 48 litres to refill.

Filled up today with the needle in the last quarter of the red range on the guage (about 1/32th of a tank) and the fuel warning. I had an estimated range left of 20-30 miles (depending whether you were booting it or cruising when you looked at the readout....)

It took just over 52 litres to fill. Which means that even though the car wasn't far away from saying "0" range, there was still about 8 litres unaccounted for - which is the same as the "reserve". All this would suggest to me that despite what the manual says, this is how the tanks are meant to work.

TBH my biggest concern is that when I got the car a month ago a fill from empty was £52, it's now £58!!!

Niall

[LetoThe2nd]

Hmm, this is interesting....

I contacted skoda (skoda-auto.cz) and I got this reply:

quote:

'the fuel tank capacity of your New Octavia 4x4 is 63 litres; The warning light and peep sound will come on if the fuel level is below 8 litres. Concerning re-filling the fuel tank you should follow the instructions written in the Owners manual: "The fuel tank is full just as soon as the pump nozzle switches off for the first time, provided the nozzle has been operated properly. You should not continue refuelling - otherwise the expansion chamber in the fuel tank will also be filled with fuel. Fuel might flow out of the tank when it heats up."'

But when I asked if this means that there is something wrong if my tank behaves differently, the answer was that this could be due to normal variance, but I can ask a dealer to check my tank....

What we need now is the same data (how much fuel can be put in the tank when the light turns on and when the car says the tank is nearly empty) - so we can see if the behavior is the same (if it is it should be around 44 and 47l respectively).

Cheers, Leto