We eliminated mine when we added the Whipple Superchargers. No T-stat either. However, our boating is done in South Florida and the Bahamas so a T stat is not the issue it would be for you up North. Our ocean temps range between low to mid 70's and mid 80's. Also, if you eliminate the circ. pump you'll void your warranty with Merc (if you're still under warranty).
Get some feed back from the folks that run in the water you experience for more accurate info.