I have an '03 Merc Saltwater 150. Serviced last summer, with waterpump replaced. Of course, no problems until out on the river late at night with another family (5 kids) on the boat. After riding through the nowake area of about 1 mile, attempted to plane. The warning alarm sounded (continuous). Water was streaming out of the rear, which appeared to be normal waterpump flow. it did seem to be smoking more than standard exhaust. I turned off the engine for a min, restarted. after a few minutes same symptoms. finally was able to proceed in this manner enough to make it to the dock. any ideas?