[C320-list] 320 #047, raw water discharge temp

[Don Poole]

Anyone know what the temperature differential between the raw water outlet and the inlet (sea) water should be? Having overheating problems with my Perkins M30 (running at 200F).  I'm only seeing a 12F temp rise from inlet to outlet when engine is fully up to running temp; unfortunately now 200F. (Measuring with a cup and an infrared temp gauge. inlet 68F outlet 80F).  I was expecting a higher outlet temp. Raw water discharge flow seems to be fine. Previously I had thoroughly cleaned heat exchanger tubes (internals) and tube bundle exterior and tested thermostat for proper opening. Used infrared temp gauge to read temp in area near temp probe and it appears that temp gauge is reading correctly. Welcome any ideas and experience!