My '89 Ford Probe has a tiny little 90 degree neck on the radiator ( plastic of course ) where the cap is.
I was on a 100 mile trip a few years back and noticed the temp was slowly rising,
I finally had to add water just 5 miles from my destination.
Upon arrival, I found that a squirrel or mouse had chewed a chunk out at the 90 deg bend,
I got some JB Weld and fixed it up, still holding years later