Removing the thermostat to have the engine run cooler is only a short term “band aid” , or something to do if you are out on the water and experience an overheat, but need to get back to the dock. The thermostat helps control water flow around the powerhead by imposing a restriction….Parts of the engine could actually run hot running without the thermostat due to uncontrolled water flow and hot spots.
I would pull that cylinder head off and have a closer look, paying attention to mumbles nice photos. I’m sure you cleaned up everything nicely, but perhaps some loose debris ended up in that passage when you started the engine. Don’t reuse the head gasket, replace it again…
