Well it still overheats at idle
I put the manifolds and risers on after soaking them in acid and flushing them. I also replaced the circulating pump.
I'm running a sea ray pachanga with stock exhaust and stock mufflers-thru hull
I'm pushing 400 hp could my exhaust be to restrictive
and cause this overheating???

I am writing a magazine article about that as we speak.
 

The water pump that you have on the Alpha drive is a high pressure design that doesn't flow enough volume at low speeds for an open thermostat system. The plastic balls are there to keep some water inside the block at idle. Mercruiser suggests installing new springs and in the worst case, stretching the springs out a little to add more tension. There are two sets of hoses running off of the thermostat housing, one set goes to each exhaust manifold and one set goes to each exhaust elbow. The ones with the plastic balls go to the elbows.
There are two styles of thermostat housings, one is where the plastic balls fit into the casting, and the other is where the plastic balls fit into a brass Tee. The style with the brass T has a gasket ABOVE the thermostat. The gasket has a section for a water bypass that is either blocked off, has a hole in it, or is open. The gasket that has a hole in it and the open gasket allow too much water to bypass the engine and dump into the exhaust manifolds. Alpha drives need the bypass blocked off with the closed gasket or the engine will overheat at an idle.
I believe your problem is that you have the wrong gasket, allowing too much water to bypass the engine for the exhaust manifolds.
Good Luck
Dennis Moore

Thanks Dennis your right.
But I got it fixed earlier today, I took 2 --3/4" fender washers and put on either side of the balls. The restriction of the washers and or the extra tension on the springs reduced the flow to the elbow. And now it stays 145 at idle. I have the closed type gasket on but didn't know if it was the correct one.
Thank you for the advice, this has plagued me for a long time. I've got your book and have learned alot from it. How about another with tips like this???
Thank You
Scott Rogers