Just finished restoring a 2550 chaparral with 454. I modified the motor with # 290 heads off a 71 corvette, crane cam, roller rockers, edlebrock performer rpm intake and 770 holley d/p. The first time out oil temp gauge dropped to zero pounds. I shut the motor down, got towed back to shore and tested with a mechanical gauge only to find out the ground strap on motor was loose. The mech guage registered 50Lb. at idle. Since, I have added a backup mech gauge under hatch. The boat has a closed cooling system.

The second time out the oil pressure was great. We dropped the boat in for the second sea trial and headed down the river. The gauges looked good, then the warning buzzer came on again. I shut the motor down, popped the hatch to find anti freeze shooting out of the heat exchanger. I pulled the water line off the top of the riser only to find zero water flow. can a raw water pump go bad?

From my experience, I change my raw water pump out every season. The impeller can pick up trash that eats it up or scars the walls of the pump. Not sure what model you have. I always check to make sure I have good flow before leaving the docks and keep an eye on the gauge at all times.
Not sure if this helped, but good luck.