My radiator fan fuse keeps burning out

Unplug the radiator fan, then see if a new fuse blows. If you have two fans, one for the radiator and one for the AC condenser, start with the condenser fan. If the fuse no longer blows, suspect that fan motor. If you spin the fan by hand and it's tight, that's the definitive clue.

Yup. You need a new motor. Without getting real technical, you need three things to generate a current mechanically, meaning a generator. That is a coil of wire, a magnet, and movement between the two. Guess what? A motor is a coil of wire, a magnet, and when you apply a current through it you get movement. A spinning motor is in effect a small generator but it's nothing we can measure or work with. The issue is when a motor is spinning it GENERATES a back current that opposes the current running it. That's why motors draw a higher current to get started, and once they're up to speed, the current they generate offsets about one third of the current needed to get it started, therefore, on average, a motor draws about two thirds of its starting current to keep it running.

To say that a different way, when the motor is locked up, it doesn't develop that back current. The higher starting current is there constantly until the fuse blows.

That's way more than you need to know to fix the problem. Find a new motor at a parts store or a salvage yard and your troubles should be over.