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I just helped my Brother -in -law change the water pump on his 4 stroke 150 (2004 or 5 model?) and upon completion we cranked it up with earmuffs and a water hose running. The water pisser took about 30 seconds to flow but eventually started flowing strong. He revved the engine a bit and the flow stopped suddenly and then a few minutes later the overheat buzzer sounded. We dropped the lower unit again to see if something was installed incorrectly but all seemed good, so we re-installed everything started the engine and the results were an exact repeat. We used a water pump kit from Yamaha for the job. We did not change the thermostats and are not really sure where they are located. This was the first time since new that the pump was changed (the old one looked fine btw). The engine has 477 hrs on it and this also was the first start after the New England winter this spring. Any ideas as to what is going on?