Put a gate valve on your inlet line off the pump. Then adjust it to control water flow and temp.

No not the cooler the better. Our engines are happy around 160-180.

👍👍👍

I have a Indmar 454 w/ a Legend pump in my boat. Seems as if the engine temp never goes above 120. Should I add a thermostat? There is no valve coming off of the water inlet from the jet. My set-up puts the water through my exhuast manifolds then into the motor and back out through the exhaust risers.

To be honest, The only reason to choke down water to the engine would be for a serious over pressure situation. Requiring a pressure guage on the water system to indicate that. I doubt it's even needed. I've installed them, but they've all run wide open anyway. 

Oil temp is what you SHOULD be monitoring. 120*-140* water temp is pretty normal in these things, provided the engine was built with that in mind, but understand the thermistor sending unit is getting whacked with new water constantly, so is REALLY not that accurate a reading. Oil temp IS.

Ray

At idle is when you want the temp to come up to around 120-140 but when cruising the temp. will go all the down cause of the constant flow of fresh water from lake/river/etc. being pumped in faster through the engine and no time to warm it up.  like IRReble said the oil temp and pressure is more important to keep and eye on but glance at water temp too.  I just look at all mine very often just out of habit. 

no band wagon here  i have been a super fan for years..  stickers on the truck and all....   yes i am drinking some