Could be nothing or a number of things.

I've seen loose water pump bolts eat a hole in the WP cover.

I'd take an OEM seal kit, the rubberized washer, and an extra impeller bolt, an extra impeller & cover if you have one or both.  Never hurts to have extra parts.

You could also just have crap in the coolant and it's stuck/blocking the line.  You could be running it wide open for too long  could be riding with the wind, etc...

Many 500s have stuck a piston making the run to duners diner on the sand highway,  wide open constant throttle is not good for 500s for long periods of time.