If wanting the new impeller to last very long and not degrade fast with use as won't be changing the old round liner, apply an overdose of any regular toothpaste on your fingertip and rub medium hard in circular motion, apply several times untill the liner has errased all those tiny circular scratches and feels very smooth when fingered rubbed.
Water pump will pump water more efficiently upwards and impeller last way loooonger!! LOL Check thermo cond, if found severely rusted, salted, degraded install a new one. With those 2 parts doing their homework right OB will cool much better provided that all water paths are clean and unobstructed.
If OB was used in salt water, put it in a barrel and apply Salt Away cleaning product, start OB and flush it at idle-neutral for at least 15 minutes, propaganda states to remove internal salt buildups well.
Happy Boating
