alarm sounding after long idle or slow cruise

[dakotadodge80]

I have a 1996 mariner 50hp. When crabbing and keeping the boat either idling or moving very slowly, the alarm will sound. If I increase the idle or throttle and raise the rpms for 30 seconds, it stops. It has a brand new battery and doesn't happen immediately. Its usualy about an hour after getting on the water. Is it a battery/power issue or overheat issue? Thanks much.

 

[Nathan Bond]

That maybe sounds like at low RPM you aren't circulating enough water through the engine, would indicate time to replace the impeller.