Jim, as a shortcut, get one of these from Amazon, they'll answer all your questions.
http://www.amazon.com/Etekcity-Laser...ds=ir+temp+gun
They're really inexpensive right now. I just bought two extras. My wife uses one in the kitchen.
After your boat comes up to temperature, just shoot the shell, where the oil is. If it's too low, 150* or so, you may need a thermostat.
I found my problem, the oil temp sender is in the pan, on the same side as the starter.
When I dropped the starter in the bilge some months ago, I skinned one of the sender's wires and it quit working. I'm waiting now to get 10 hours on the engine so I can change it and the sender.