my moomba overheated and shut down last week at 190 degres. the sensor does this for safety reasons. I inspected the raw water pump and it looks fine so I replaced the thermostat with a 160 degres thermostat. My temp gauge is reading around 175 to 180 and the safety sensor shot my boat down again. My temp always used to hover around 140. Anybody have any idea what is causing these high temps?