Whilst diagnosing another issue with our 2001 P38 I noticed that the water hose than runs up and over the top of the alternator belt and into top of radiator had an unusual bugle to it. It was adding about 15% to the diameter of the rest of hose. I turned engine off and slowly opened the expansion tank cap and the affected area of hose decreased to its normal size. Engine cluster temp gauge rads 12 o’clock position and an infrared temp reader shows constant temp along hose from engine to top of radiator. This section of hose appears to be full of air, however, the small hose from top of radiator shows a constant flow of water when engine is hot.
I’m assuming that this is not a normal condition but am reluctant to change a hose just for the sake of changing a hose. I followed the manual for bleeding the air when I installed this hose two years ago.
Thoughts?

It's a faulty hose, it has an aneurysm. No different to getting an egg bulge in a tyre cause by internal de-lamination.

Appreciated…..