I just got my first boat and got it running after sitting 10+ years.  My question regards plumbing.  The water intake hose from the transom to the engine came with 2 (assemblies).  1 is a simple T which I used to provide water to get engine running.  The other replaces the water inlet with a valve.  I will assume that this is used when boat goes in water so what is the technique used with the valve?  Thanks for your help, don't want to blow things up by not asking questions first.  No ego here...

what am I targeting as a temp? 140-160?

What engine? BBC or BBO water temp/pressure is important to set...BBF not so much. I run my valve all the way open all the time with BBF. When I had an olds it was around 160-180 with just off plain/cruise spikes up to 200. Olds will crack in water jackets around valves with to much water.

IMHO anything above 160*F is too hot.

Basically, depending on the total set up, with the boat idling at the dock, turn the valve toward closed at idle until the temperature starts to rise. I like to see about 155* at idle for a start.

As the engine speed increases the temperature should fall fairly quickly. On a Berkeley pump, the temp should be around 120-130* if everything is sized correctly.

Unless the engine has an automotive style water pump on the front, stay below 155*, there is NOTHING circulating the water within the cooling jackets on a jet. So 170*F at the gauge means that many areas in the block will be in excess of 220*...

GT