Here in India, I change my fuel filters every 5000 km, this is with regular dose of DALF additive from ELF. I have also attached a sedimenter which collects all the algae and gig particles as well as tar. You should see what ends up in the filters and the sedimenters after 5000km. It is a lesson to be learnt. I have both the felt pre-filter as well as the paper filter. It is good to spend on filters than servicing injector and pump.