First, read Job 41 in it's whole, here are some highlighted verses that don't seem to even remotely describe a crocodile.
Job 41
12 "I will not fail to speak of his limbs, his strength and his graceful form.Would a crocodile be described with a "graceful form"?
18 His snorting throws out flashes of light; his eyes are like the rays of dawn.Several references to breathing fire, flashes of light, flames, sparks, smoke. This is not just a passing note, but something significant about the Leviathan. It doesn't describe a crocodile.
19 Firebrands stream from his mouth; sparks of fire shoot out.
20 Smoke pours from his nostrils as from a boiling pot over a fire of reeds.
21 His breath sets coals ablaze, and flames dart from his mouth.
24 His chest is hard as rock, hard as a lower millstone.The crocodile's chest and belly are made of smooth scales. They are soft, not rock-hard.
30 His undersides are jagged potsherds, leaving a trail in the mud like a threshing sledge.The crocodile's chest and belly are made of smooth scales. They are soft, not rock-hard.
Psalms 104:25-26, "There is the sea, vast and spacious, teeming with creatures beyond number— living things both large and small. There the ships go to and fro, and the leviathan, which you formed to frolic there."Do crocodiles live in the sea? No, they live in "grassy swamps and slow-moving rivers", not anywhere the ships go.
Isaiah 27:1, "Leviathan the gliding serpent, Leviathan the coiling serpent;"Have you ever seen a coiled crocodile?
Just taking a surface look at the scriptures description of the leviathan give ample reason to reject the idea that it is a crocodile. What do you think?