overheating
 

hi everyone i'm looking for some help. I have a 95 240z talari with a 454 carb and a brovo 1. from My temp gauge goes back and forth from 160 to zero. It has a new 140 degree thermostat. The sea pump was replaced and everythins like its g seems to be circulating. But it acts like it might be sucking air. after running the boat it sounds like its boiling in the engine. If you let the boat idle before shutting it down it's fine. But if you stop to let in a skier the engine seems to hot. My mechanic cant find anything wrong. Has anyone run into this problem?