i have a 1989 40 hp mercury 4 cyl which i overheated while idling. i had to change out the power pack and the voltage regulator as well as the water pump. it runs fine, but after about 20 minutes of running, the overheating alarm starts chirping and continues to get louder as i run. the water it is peeing is hot so i assume it's cooling the motor. the block doesn't feel overheated. is there a thermostat on this motor that i can change? any help would be appreciated.