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[Alex]

Overfilling can damage the fuel evaporation canister (a charcoal filter with some valves and other bits) because you risk flooding it with liquid gasoline instead of relying on it to draw in the fuel vapors from the tank and then purging them in specific conditions through the intake manifold to be burnt inside the engine.

Running it on an empty tank can also damage your fuel pump or injectors.

[CrazyG]

Thanks for that simple yet informative explanation Alex.....

So now we all know, eh !   

[NSquirrel]

Thank you Alex and CrazyG.

[Alex]

You are both very welcome, and thanks from me too for having me on here with all you great guys (and girls).

The rollback is awkward, and they should really address this issue.

Maybe try and see if it also rolls back with the start stop disengaged at those same problematic traffic lights.

[NSquirrel]

Thanks Alex.

>>Maybe try and see if it also rolls back with the start stop disengaged
It is at the garage as I refuse to take it back until the problem is corrected. Smart UK Customer Service will hopefully assist now is resolving. I think that they should try it going up a busy multi storey car park a few times with some big burly bloke in the car behind who is in a hurry; it certainly checks the Adrenalin system, especially as it is seemingly intermittent.

We will get there -eventually. Have a  good weekend

[NSquirrel]

The fuel tank query is curious. The user manual indicates that there may be either a 28l or 35 litre tank, including 5 litres reserve. Doing my best to do Smart's work, I gather that the German new series ForFour Smarts have a 28l tank and all of the UK models 35l. My tank was confirmed by the garage as being 35l; they finally tested it, when checking the fuel gauge, rather than just looking at the spec. sheet. (My observations would have been quite within the bounds of a 28l tank, although that would have made the tank questionably small for my use.)

Now I am not trying to be pedantic and I do not go looking for problems, but sometimes something appears odd -in this case why the tank only took 10 litres to full from half full and 20 litres from almost empty. So, 'if all else fails, I read the manual' as I may be doing something wrong. The manual says ' Insert the filler neck of the fuel pump nozzle all the way into the tank and refuel. Only fill the fuel tank until the pump nozzle switches off. The fuel may otherwise leak out. Overfilling the fuel tank can damage the fuel system....'

To me the key point is 'all the way' and the filler nozzle/ dispenser does like to sit in all the way. I assumed that the end of the nozzle would therefore be above roughly the top of the tank, but I think it may be well below the top. The diameter of a fuel dispenser is fixed by standard, so we don't -hopefully - put diesel in petrol cars, etc. Is the length of the nozzle also subject to the or a standard? Searching last night I got as far as UL 2586 being the standard, but I do not want to have to pay several hundred pounds to read it.

So if the end of the nozzle/ dispenser is below the top of the tank and overfilling may damage the fuel system (thanks, again, Alex for the reason) what is full and what is overfilling? I would say that all my previous cars -an English car (-OK, I admit it, we bought an Allegro a nightmare ago), golfs, Mercedes, Smart ForTwo, the top of the tank was seemingly a long way below the reach of a filler dispenser.

Interesting to a retired engineer (electronics)

(Btw, just to repeat, I am not trying to be pedantic or imitate Victor Meldrew; it is the damage to the fuel system that raised my concerns. Even I can spot overfilling so that petrol comes out on the forecourt.)

I will be interested to see what comes back from Smart; perhaps just a simple change to the User Manual.

[Alex]

If you have the time and can be bothered, after filling up until the pump first clicks, go around the petrol station a couple of times and try and refill it again until it clicks.

If it takes a good few liters to fill up again it means the tank has a funny contour and the fuel takes a while to fill all the chambers, but the pump clicks off because it's too high flowing. If it clicks right away though, that's how much it takes and perhaps the fuel reserve figure is very....reserved. Again if you fancy, drive it until it shows 0.0L remaining and refill it..But have 5L in a jerrycan because you never know how good the fuel readout is..

I've driven mine almost 60kms after it said 0.0L and refiilled, 43L in a 47L tank. So there was loads more petrol in there, but there needs to be a lot in the tank for the pump not to overheat, so the car tries to protect itself from lazy drivers that put off refilling until the last moment.

Also if it's very little it might not start in the morning, or you can get vapor lock...

Also, the fuel sender says FULL even when the tank is just 90% because the fuel sender float is floating on top of the fuel, so it's height takes up the 10%... only when the empty space in the tank is bigger than the thickness of the float does the readout start dropping.