i just got my boat back from getting the topend refreshed, engine is a 500efi. Took it out yesterday and there was some issues with the temps. boat warmed up and then kept creeping up to above 200. got it on plane quick and it cooled down to around 180 or so. stopped and started getting up well over 200 again engine buzzer was going off. I dont understand what the problem is. they replaced the seawater impeller. I took all the hoses off today looking for a blockage and didnt see anything as well. I did see a little bit of steam coming out of the exhaust but I wasnt sure how normal that was because the water temp is only 45 right now. Also i lifted up the engine hatch while running and exhaust and intake were not hot, just slightly warm is all. Any ideas?

Do you have a thermostat or crossover ? I would check thermostat. also if you have a cooling hose easy to access take it off make sure its pumping.

You have closed cooling right? Do you have holes drilled in the tstat? It sounds like air pockets in the engine. If you don't fill a cc engine with antifreeze correctly you will get this.

Make sure they put the T-Stat in the top of the housing and not down against the intake manifold. Made that mistake and the temp. will cycle up and down