A thermostat will help prevent exhaust valveseat cracks, and will give a fuel economy gain. Other than cost and looks, there is no downside to a thermostat setup. OT headers are especially hard on cylinder heads as there is no preheat. Most cracked heads have installations that restrict the water to the engine to help it run warmer. The problem arises when after a hard run, the motor is shut down and the water in the engine drains back into the lake, leaving a dry, hot cylinder head. Then before the heads cool, the engine may be restarted and the driver stomps the throttle. With the engine empty of water and the incoming water restricted, it may take up to 40 -50 seconds of full throttle operation to fully fill the engine with cold lakewater. This cold water then hits the hot head and causes cracks in the hottest area of the head, around the exhaust valveseat area. On the jetboat engines with OT headers that we rebuild, about 1 in 5 heads are cracked, and about half of those are not repairable. TIMINATOR
