I have an issue with my rebuilt 4.3l mercruiser running hot. I had it on the muffs in the driveway to roughly set timing and the carb. The engine ran for a total of 5 or 10 min a most. I didn't check temp but I had a buddy make sure water was coming from the stern drive so it was circulating. I put in the lake and took it about a mile never going above 3000rpms to break it in and notice the temp gauge was reading a steady 220 degrees. I immediately shut it down and floated/paddled the rest of the way to the dock, about 20yards, so I wouldn't cause major damage. I let it cool down to about 120 degrees and check things. There was water in the hoses so I pulled the inlet hose from the transom to the engine and bumped the engine over to make sure the impeller was pumping and it was. The stream was like pouring out a bottle of water. The motor only ran for a second. I pulled the thermostat to test it and it works fine so now I am back to square one. I have a feeling it?s the impeller but I am not sure. Is that what it sounds like or is the engine just running hot due to breaking it in? Please help.
