Brand new Mercruiser overheating

[vanderd]

My son’s 33 ft Maxum has 350 block engines with Bravo outdrives. The starboard engine was just replaced (brand new not rebuilt). New exhaust manifolds & risers and new raw pump. It’s a FWC engine. It can run for several hours and then the temp climbs and high temp alarm goes off. Other times it gets hot much more quickly. We’re stumped and the mechanic stands behind his work but hasn’t been able to figure it out. Any thoughts? We’re getting frustrated. Thanks for any thoughts.