I have a 1989 Sea Ray DA220 with...

[BAT_Man]

I have a 1989 Sea Ray DA220 with the Mercruiser 350 5.7 liter Alpha 1 engine. The engine seams to overheat during idling. I've replaced the impeller, and changed the thermostat. When I increase speed from idle the engine cools down to 145 / 150 and runs fine. When at idle the engine temp eventually goes up to 220. It doesn't seem like the engine is really that hot but am worried if it is I could damage the engine. Water pours from the foot as it should so I'm not sure what to do from here. Has anyone experienced this? I'm open to any suggestions going forward. 

Thanks in Advance!    

[LADONNA]

Check for impeller pieces at the inlet to the raw water pump. The opposite side you would think they would be.

[Bow_Tie]

After you determine the impeller is good. There is a circulation pump Monday the front of the engine. Sometimes they go bad. Pull the heat exchanger cap off (when cold) , check to see that coolant is flowing through the heat exchanger. Also, if you pull the exhaust hose off the raw water pump you can check the volume and pressure of the raw water coming out of the pump. There should be enough water to putout a house fire! Or you could measure it and calculate how much water per minute its pumping.

[101Marine]

How hot are your risers getting? I presume its raw water cooled or is it fresh water cooled? You do need to have a good engine circulation pump and impeller. as they work together. A temp. gun is cheap on Ebay and can help look at what is getting hot first. The Alpha's have the impeller in the leg and there is a transfer hose - that could be leaking? When was the bellows replaced?

[Wheeldude]

Actually a pretty common problem. I assume this is raw water cooled. The thermostat housing has two hoses coming out at the top that go to the risers. If you pull those hoses off at the thermostat housing, you will find a nylon ball on each side that are connected with a rod with a spring on each end. What happens is that over time, the springs loose there tension and that allows too much water to bypass the engine and go straight to the risers which causes the engine to run hot at low speed. Take the nut off the rod and stretch the springs a little to bring back some tension. While you're at it, make sure the balls are in good shape and are seating into the thermostat housing properly. Should take care of your problem.

[BAT_Man]

Thanks guys for the quick response. I apologize for not responding earlier. I will check the areas recommended by you guys. The engine is raw water cooled.