Product review (5 stars): 250-40 vs 250-80
If the fuse is blown which is the one that has the highest temp. Rating  in  Fahrenheit example 309F or 352F. Then you probably have a bad thermostat. You need to replace both. Now the  difference between 250-40 and 250-80. The second number is the differential. So the 250-40 is on between 250 and 210. And the 250-80 is on between 250 and 170 degrees. And FYI FSP MAKES THE OEM PART. hope this helps.