Hey guys, searched for this but no cigar
I always thought that it doesn't make a difference, but I heard some people say that you're meant to refill before the needle goes down to the last 1/3 or 1/4 or so (something to do with direct fuel injection/clogging up your fuel filter???). I tend to refill when the light goes on. The fuel gets sucked from the bottom of the tank anyway, doesn't it?
If you refill at 1/3 full every time, won't that mean you will just have more and more % stale petrol in your tank for longer?
eg.
1st tank: 1/3 batch A, 2/3 batch B
2nd tank: 1/9 batch A, 2/9 batch B, 6/9 batch C
3rd tank: 1/27 batch A, 2/27 batch B, 6/27 batch C, 18/27 batch D
etc, etc you get the idea
Granted stale petrol will never reach more than 1/3 of the tank, but with each filling, a smaller fraction of that petrol you put in last year still remains...