The lower of the two coolers was usually used to cool the engine
oil on its way to the remote oil filter
, and the upper of the coolers was used for the hydraulic transmission
. The reason the coolant
isn't shooting out of the two open fittings is that the coolant is flowing inside the tubes which are inside the outer shell. Normally the transmission
fluid is found outside of the water tubes but inside the outer shell.
As for the overheating
engine, go thru the normal drill of restrictions, cleaning
, etc. on the seawater and freshwater circuits and you should be able to control it somewhat.