It is powered by two Volvo Penta 5.7 engines. It also seems to overheat when I turn to starboard sharply.  After I shut the engines down it reads normal on the gauge and if it doesn't, once I throttle up the needle immediately goes back down.  I have had it peg to the top but never activate the overheat alarm or shut down. I have had the thermostats replaced and the impellers, my mechanics can't seem to figure this one out.