I have a 1970 Proline 21' boat with an out board motor. The last few times I have taken the boat out, after about an hour of being on the water, a gauge that appears to be some sort of a radio wave signal begins to beep. It stays on until I shut the motor off. Once again after about another hour of operating, it will start beeping again. Is this an overheating situation? Any guidance would be appreciated.