[tevake]

You could check for obstructions in the water outlet line. Used to get chunks of sand blocking the line right where it connect to the nipple where it goes through the shroud.
Does sound like lack of cooling water flow. Lime out may help to break up salt/corrosion blockages in the passages. Thats where I would start looking next.

Then back to the search for the perfect fishing gear.

Pipe cleaners just came to mind.

Cheers Richard