'98 Yam 250hp OX66 overheating

[hoppyray]

My buddy has an 1998 Yamaha 250 hp OX66 that overheats. It will start fine at the dock and after 5 minutes warming up he will take her out and once under way gets an alarm.
The motor is overheating and he will slow down to idle but it keeps overheating/alarming. He will shut it down and let it cool then fire it up and it will run fine and will be fine all day. Sure sounds like stuck thermostats but they have been replaced twice. Could it be anything like the old vapor lock problems? I thought maybe a bad temp sender but he said the motor did get hot. I have the identical motor but never this problem. Anyone got any ideas what to check next or what could bethe cause?
Thanks

 

[Captain Paul]

Re: '98 Yam 250hp OX66 overheating

A history check of this board my prove helpfull. Pressure relief valve stuck perhaps? That was a recomended fix for a slow rpm overheat on muffs for my OX66 and although it really didn't seem "stuck tight", it worked.