2006 SUZUKI 90DF. 300 hours. Water pump and impeller installed 6/2019. Just started motor up in water. Delayed telltale stream but it did start after 20-30 seconds. Idled for about 10 minutes. Steam started coming from exhaust, alarm went off and temp light came on. Engine turned off on its own. Checked the poppet valve did not have any debris that seems to keep it from working properly. Pulled thermostat. Found thermostat opens at 140 degrees. Checked water intakes and they appear to be clean. Started engine again. Left idle and fast idle about 2000 RPMs for about ten minutes. Telltale working. No alarms. But a larger amount of steam again suddenly appeared from exhaust port and I turned the engine off. Pulled spark plugs, all four look normal and not steam cleaned. Oil looks good, no milky appearance seen. Ambient temp 60 degrees. Water temp 48 degrees.

Where do I start now?