Hey, guys. I have a 2019 Superb, and i normally fill the tank full with 99 octane fuel (from Tesco). The guage always moves to full, and the range adjusts accordingly. Yesterday, i was running low - range: 15 miles range - and decided to fill a small amount - 6l - of 95 octane. After driving off, i noticed the guage hadn't moved and the range was still showing as 15 miles. So, i decided to fill another 6l at a different fuel station. Same issue - in fact, the range has now dropped to 10 miles. 12l should easily have taken me out of the red! Has anyone come across such a thing before?

I’m sure someone had it on here where it registered as empty but still had like 5+litres left l, fill it more and it should be fine

Yes, ive seen that somewhere as well. I realise the range figure isn't all that accurate. But filling 12l should have taken the gauge out of the red. But it didn't move at all. It's as if the car didn't realise it had been filled. That is simply odd.

It becomes clear when you realise how most modern trip computers work. They are designed to expect a reasonable amount of fuel to reset/recalculate post refuel - 6 liters won't have been enough. Equally neither was 12litres, because that's not what happened - it will have seen 2 separate fill events.

It's clever enough to know that, but not quite clever enough to be able to reset on such a small amount of fuel. 12 litres in one hit probably would have done it.

Edited 20 July, 202520 Jul by AlistairCookie

19 minutes ago, AlistairCookie said:

It becomes clear when you realise how most modern trip computers work. They are designed to expect a reasonable amount of fuel to reset/recalculate post refuel - 6 liters won't have been enough. Equally neither was 12litres, because that's not what happened - it will have seen 2 separate fill events.

It's clever enough to know that, but not quite clever enough to be able to reset on such a small amount of fuel. 12 litres in one hit probably would have done it.

This^

If you treat it as an estimation device, you’ll be in better stead. My Octavia is similar.

10 hours ago, AlistairCookie said:

It becomes clear when you realise how most modern trip computers work. They are designed to expect a reasonable amount of fuel to reset/recalculate post refuel - 6 liters won't have been enough. Equally neither was 12litres, because that's not what happened - it will have seen 2 separate fill events.

It's clever enough to know that, but not quite clever enough to be able to reset on such a small amount of fuel. 12 litres in one hit probably would have done it.

Is there no physical float in the fuel tank that moves the dial needle on the dashboard? Or is that dial also computerised now?

The sender unit still has a float, but it's not linked directly to the dial. That's the case for probably most cars made in the last 20 years.

2019 Superb the fuel gauge is only an interaction as to the fuel level.

In my experience adblue systems are the same. Even half filling them will sometimes not register.

If you consider that the fuel in the tank sloshes around a lot while driving & when stationary it does not know if the car is tipped or inclined causing the level to change compared with what is really there you can understand that when adding a small amount of fuel the car will take an average reading of some time before deciding how much fuel is there.

There will be a threshold like 20% over which is will register more quickly a refill amount.

In this situation, you know you've added 6l of fuel so you can drive it until the system is able to catch-up.

Especially in a petrol car, it won't stop if there is really fuel in the tank even if the distance to empty says 0 miles

On 20/07/2025 at 17:40, Danoid said:

I’m sure someone had it on here where it registered as empty but still had like 5+litres left l, fill it more and it should be fine

On 20/07/2025 at 17:49, Aciduzzo said:

Yes, ive seen that somewhere as well. I realise the range figure isn't all that accurate. But filling 12l should have taken the gauge out of the red. But it didn't move at all. It's as if the car didn't realise it had been filled. That is simply odd.

It may be me that reported this on my ex Mk3 TDI190.

I can't remeber why i did not want to fil a full tank, but I also started with 5l or so. And autonomy remained the same. I then topped up anotehr 5l and still faced the same problem. I finally ended up with maybe another 10l top up or so, before the autonomy went up again.

I guess this is linked with the fuel gauge, which is incremental instead of being continuous. IMHO, this would also explain why the "volume to be replenished" displayed on the dashboard has 5l steps...

As it happens, I did a small topup this morning for the commute to head office and back. Put 11 litres in and it updated the range accordingly.

12 hours ago, AlistairCookie said:

As it happens, I did a small topup this morning for the commute to head office and back. Put 11 litres in and it updated the range accordingly.

That's useful to know. I suspect the threshold for the car to register the fill is around 8-10l.