2002 Mercury overheating to about 160 to 175 degrees. Poppet valve stuck partially open, replaced. Pump, thermostats, grommets were replaced when the motor mounts were replaced last fall. Checked the head temperature using infrared gun. Thermostats started opening at about 130 degrees(small trickle) and at around 140 degrees plus I was getting full flow. Water pressure at idle right under two pounds( and yes this is the correct pressure for this engine). Temperature checked at all spark plugs in two places - about a 1 1/2"(flat spot on head) horizontal to the plug both left and right side of plug. Why? On a previous test I noticed the middle cylinder right bank was running about 15 to 20 degrees hotter than all the rest of cylinders but was only this hot to the right side of plug. The left side was hitting about 139 degrees. All cylinder head temperatures were higher on the outside both left and right heads. The top cylinder left bank reading about 148 degrees both sides of plug and only cylinder that did not have an increase in temperature to the right of plug? Don't have any idea how the water flows and all I can figure out is the flow is directional and something is blocking that flow on both exterior sides of head. Also in the Mercury cooling flow diagram how can you have a line on the pressure side and it be called a discharge line???
