I have a 1983 31 with a Yanmar 2GB and my water temp alarm goes off after about 5 minutes. I have a new water pump (even put a new impeller in it). Checked the belts, it's turning. I now the thermostat is working (even tried it taking it out). Water is coming out the back. Cleaned the strainer. It is a raw water cooled engine (no radiator}. I let it cool down, starts up without the alarm, but a few minutes later, you know that shreik starts again. I just can't figure out why the alarm keeps going off, any suggestions?