1975 searay 240 mercruiser 233 ford 351 overheating

[Shanerbones]

My 1975 searay ford 351 is overheating and I cannot track down the issue and in need of help... last year I changed impeller and then thermostat now I have changed hose from outdrive and went through manifolds and risers. Also changed gauge and sending unit and I believe it has restriction somewhere and not getting enough water. I am lost could use any suggestions thanks in advance

 

[kenny nunez]

Has the water pump ever burned up and caused the engine to overheat in the past? What condition was the impeller when you replaced it? If the plastic pocket cover in the upper housing has melted that could be the cause, once they melt they will leak and not enough water will get to the engine.
If there are no restrictions in the engine’s cooling system this must be checked. Drop the lower unit and take a look.

 

[Shanerbones]

Old impeller was in perfect shape maybe just weak. Pulled hose off of thermostat housing and water was flowing just dont know if its enough

 

[wahlejim]

If your engine has overheated in the past, check your exhaust flappers. They may be toast and restricting water flow. If they are malfunctioning, chase all of the melted pieces out through the outdrive.

 

[Shanerbones]

Il check them out thank you

 

[Lancer76]

When you say you changed the hose from the outdrive, do you mean the one on the inside if the boat that attaches to the water pump? If so, it's possible that the hose from the water pocket to the transom is kinked and restricting flow. The hose is outside the boat and delivers the water from the water pocket to the outside of the through-transom fitting. Speaking of water pocket, check that, too. It can overheat and become disfigured.

Knowing when it over heats can be helpful info, too (e.g., during idle, only at high RPM, etc.). An infra red thermometer can be useful for diagnosis, too. Cheap tool at harbor freight.

Good luck. Chased down an overheat on my 351w a few years ago. Took a while, but it was the transom hose. Compared to your motor, mine is practically brand new - it's a 1976.