1994 Johnson 70hp oddly overheating

G'day all, currently have an engine in the work shop displaying very odd over heat alarms, constant beep, so far replaced complete water pump assys, thermo assys including diaphragm and springs, cylinder head gasket also, oddly the engine does not.overheat with the thermo taken out, yet the thermostat tests fine, and also checked with another one in stock. Had a.temp gun all over the engine, engine temp gets to 180 on the heads, and buzzes when temp reaches 164 at the sender. I have tried.removal of gearbox and force feeding it water, still over heats with the thermo, however has a great tell tail stream. When I remove the thermo for this. Test I notice the tell tail is weak but the engine.only sits at 80, however the.engine dumps alot more water from the exhaust tube, any ideas where to look next? Short of removing the powerhead and checking the water tube grommet,

Thanks.

Does anyone know what temp the temperature switch is.activated at? Thanks.

After further on water.tests conducted. The engine.run cool without the.thermo.and diaphragm assy. However pumps little water and instead directs it down the exhaust, I have tried other thermostats and tested them thoroughly, any ideas!?