So i just did new heads on my 454 due to the previous owner selling me a boat with a cracked head. There was some sandish looking stuff in the water jackets and the marina said that it was normal. Any way got it back together and runs great! Had it out 3-4 times with no problems. Today i got my timing adj finally and i took it out. I drove around a bit with no problem then got to a no wake area and idled threw. Coming back threw all of a sudden the motor got hot. Couldn't touch the risers. So i shut it down let it cool a lil and restarted it then the temp started dropping and went down to 160ish. still while idling. So i got it on plane and drove around again with no problem then all of a sudden still on plane about 3500 rpm's it started to get hot again! So i idled back to my dock cause i was close and it got up around 220* and thats where it sits. What do i check first?