Engine runs about 175 below 3000 RPM then climbs above 200 after 3000 RPM, go back below 3000 and temp. falls to about 175. Seawater pump has had a new impellar installed and still did not fix problem. However when you look in the sea strainer it appears to be only about half full with engine running. Shouldn't it be full? Could trouble be between water pick up and sea strainer? This problem has gradually manfested it self over a long period of time, Gradually getting worse and worse.