Tried to pull my water pump impeller the other day, it's stuck in there real good. I was using pliers and all the leverage I could get on it. Any ideas? I'm thinking spray penetrating oil on the spline.

Also, my boat overheated the other day, hence I assumed the impeller was bad. I was feeling it with my hand, and all the vanes still seemed intact. Any idea what else could cause the overheating? I've never had an issue before with overheating in any boat other than a bad impeller. Is there a way to test if the motor is getting water or not? Maybe my thermostat is bad?