Is it like in the car where you have no fuel left but there’s a reserve of another 10 liters?

Yes and no. I had this happen recently and looked into it.

My wife has been using my car, which is a Diesel Golf with a fuel capacity of 14.5 gallons. We set off driving one Saturday to visit my parents, and I noticed the fuel gauge was below empty already. By the time I got to the gas station, I put 14.3 gallons of fuel into it. I calculated that that works out to be about a cup and a half of fuel.

So once you hit empty on my car, you definitely have a ways you can drive still. I feel comfortable driving about 30+ miles, and it's never died on me. That puts it at no more than 1 gallon of fuel left in the car based on my experience (not scientific I know, but I've owned 2 of these cars, with about 190k total driven miles). It's a lot less than 10 liters from E to Dead on the roadside.

You shouldn't tempt fate with a diesel, or any direction injection car for that matter. The high pressure pump will shred itself very quickly as the diesel is used for lubrication.

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Best Practice.

probably depends between cars. on my old civic fuel light is ~5L/1.3 gallons

It's more like

* enough reserve to waste some in traffic. On top of that * enough reserve to find gas station. On top of that * enough reserve to drive to neighbouring city for gas station. On top of that * enough to cruise 30 minutes around that neighbouring city looking for other gas station in case the previous ones were closed. On top of that * enough station to run around parking lot looking for space to park