The impeller is cooled by the ocean or lake water that it's pumping. It's a good idea to get a baseline reading on this as well. If you develop and blockage of your intake or sea strainer the temp of the raw water pump can climb due to less water flow and thus less cooling.


It will normally read a little hotter than the ocean temp as measured on the outlet side and this is normal. This reading, even with a brand new impeller, should still be well bellow 10 degrees.