All those early Cherubini Hunters had QM series Yanmars (with the exception of some of the larger boats that had the 4JH series in the 80s). The QM series diesels had heavier, beefier castings, weighed more than the later GM series, and were designed to be raw water cooled. Though there was a fresh water cooling option available from Yanmar, Hunter generally installed the raw water version and converted it with a heat exchanger from Sendure, a manufacturer in Florida. If your boat has either an L-shaped thing or two double stacked cylinders with hoses and has a rad cap, your diesel isn't raw water cooled. The QM also doesn't have a 'dipstick' under the oil filler cap - it should be low on the starboard side of the engine block, under the exhaust manifold. If you go to the "Downloads" section here on SBO, you will find both operator's and service manuals for your engine. And, yes, that warning light and buzzer going off with the engine running usually means there's a problem with the cooling system; ignore it at your peril!