it all depends on how much crap is living in your tank/fuel system. On my VW B4, 240D, and 300TD, all three clogged within 60-100 miles of B100 dose. and on the B4, it clogged again after a winter of dino-fuel. Bottom line is that if you run high percentages of biodiesel, its smart to carry atleast one set of extra fuel filters and necessary tools to change them. Symptoms of the clog - You'll notice that the car will start to have problems holding speed, poor acceleration, and the engine may even begin missing. Change out both the filters in about 5 minutes and you've got a new car. It also seems that B100 increases the frequency that i've had to change filters noticeably but not drastically. You can get some cheap backup Purolator filters at most autozone type places for about 15 bucks. good insurance.