Just installed An IMCO adjustable water pickup & was wondering if 140 degrees is a good engine temp. It is a 502 with mild engine work. It's run in the Atlantic ocean if that helps.

The big question is "did it change from before?"

Oil temp is way more important than water temp. Too cold and condensation will dilute it until it no longer lubricates well and smokes your motor. Too hot... you already know.

On water, pressure is way more important than temp. If you lose an impeller, the intake manifold will be the first thing to not have water in it. The steam from your self-destructing motor will keep the gauge sender warm enough to read normal until long after it's too late.

Its not to bad i think,but what is your waterpress. ?
WOT should not be more then 18 PSI !!!!

Water pressure was 10 to 12 psi wide open. Is it common to have air in the line. It is the first pressure gauge for this boat, so I have lots of possible ??

Probably not air in the system.
Do you have a full raw-water system or does it have a circ pump?
If it's full raw water, does it have a thermostat?
How old is the impeller in the pump?
Standard Mercruiser belt-run pump?
Anthing in the line between the hull pickup and the pump intake, like a cooler?

Any restrictions in the line between the pump outlet and the engine (coolers, strainers, elbows, etc?)

Knowing these things gets us started.