anyone know why #8 fuse under hood blows intermitenly on short runs

Get a few fuses and see which component makes it fail. Your best bet of finding it is to TRY to make it fail. Once you learn how it fails, you'll know how to fix it. Shake wires, play with connectors, and make sure your fuse is properly sized. Also, it may be the combination of two or more components that make the fuse blow.