Unresolved

Why do cars ran out of fuel?

It's not a bug as such, it's a difficult balance and made more difficult with some circuits having less than 2 litres/lap fuel consumption making the tolerance very tight.

A couple of years ago the game was conservative and would sometimes send a car into the pits a lap earlier than expected when the car had just enough fuel remaining to do another lap (or at least coast into the pits). So the Devs reacted to feedback and made the pit calculation less conservative which now results in cars sometimes not pitting when they don't have quite enough fuel to do another full lap.

Either way can destroy a race. Pitting early when you have just enough fuel to do another lap can result in a late unplanned pit stop whereas the current settings can result in the car coasting the final part of the lap which means a slow in lap and lost positions.

If you're attending and managing the race your PL can cause problems. If you use a very high push level on your "in lap" it will increase fuel consumption and can result in you running out of fuel towards the end of the lap.

Personally I would like to see the Devs remove the pit stop / fuel trigger altogether and leave it up to the manager to tell the driver the lap number to pit. Then if you run out of fuel or pit with 10 litres remaining it is your fault for getting the calculation wrong. I mean, it's not difficult, if your practice lap says 2.43 litres per lap and you want to do 10 laps you're going to need 24.3 litres. If you only load 24 litres and run a high PL the chances are you will run out and DNF before you get to your planned pit stop. Conversely you could choose 27 litres, you'll definitely get to your pit but may be carrying an extra 2.5 litres of fuel for the entire stint which will slow you down.

It is not a bug. The cars that retire at lap 65 do so because the managers have not logged in and repaired the cars for a number of races. They DNF because they break down, not because they run out of fuel.