I have a Mercruiser MAG 350 with Alpha drive. Engine is running well overall. Temperature will climb up to 180 if you run at full throttle for a while.... might go higher but I usually back it down before letting it. Slow it back down into the 3500+ rpm range and it will run in the normal cool range. In fact, if you just do a normal cruise around the lake you would never see any issue. Only when full out for a while or pulling tubes and skiers for a while do you even see an issue. Impeller on outdrive has been replaced. The engine block was replaced 5 years ago... Cooling setup is standard seawater cooled MPI Alpha model oM300000 and above. I have attached a picture of the water flow diagram. Other notes: water circulation pump, thermostat and distribution housing are most likely original. No obvious kinks or leaks in any hoses. I have not done any kind of backflush yet. Did not have any obvious event that occurred before this issue.(ie suck up stuff off the bottom, or other failures) At this time thinking I have some level of partial blockage somewhere that is restricting flow. Before I start pulling hoses or parts, I wanted to get some opinions on the best place to look.