After a lavish floor repair I decided to start the motor-mercruiser 170 with 4 inch heat exchanger.I put on the muffs and turned the tap on .Surprisingly it started on half turn and idled sweetly.Almost immediatly noticed that no water is going outside the prop.Kept an eye on the temp gauge and when it aproached 175 I turned the engine off.The manifolds were hot ,the hoses were hot, the heat exchanger was hot but no water getting out of the boat.What could it be ?Please help me with your knowledge to solve the problem!Thanks!