225 HP Mercury Outboard Overheating problem

[wrg49]

I have a 225 HP Mercury outboard on my 1994 24' Explorer. I assume the engine is original (I bought the boat used - approx 850 hrs) My problem occurs when I get up on plane and am going along at about 3000 rpm. The temp sensor starts to rise and eventually the alarm goes off. I shut the engine off to rest the alarm, wait a few minutes and restart it. If I then run at around half throttle, the temp will settle in at a much lower temp.The water flow indicator shows good flow. I spoke to the marina where I bought the boat and he assured me that he replaced the water pump impeller and thermostats prior to sale. I flush the engine after each use and have begun using SaltAway (with some good results)..Anyone have any idea/advice as to what is going on? I'm thinking of pulling the thermostats out to inspect/replace but would rather not. Any ideas ??

 

[seasick]

I have a 225 HP Mercury outboard on my 1994 24' Explorer. I assume the engine is original (I bought the boat used - approx 850 hrs) My problem occurs when I get up on plane and am going along at about 3000 rpm. The temp sensor starts to rise and eventually the alarm goes off. I shut the engine off to rest the alarm, wait a few minutes and restart it. If I then run at around half throttle, the temp will settle in at a much lower temp.The water flow indicator shows good flow. I spoke to the marina where I bought the boat and he assured me that he replaced the water pump impeller and thermostats prior to sale. I flush the engine after each use and have begun using SaltAway (with some good results)..Anyone have any idea/advice as to what is going on? I'm thinking of pulling the thermostats out to inspect/replace but would rather not. Any ideas ??

If you are lucky, there may be some blocking of the water inlets. Take a look at the lower unit to see if the inlets have any gunk on them. Since the temp rises under load but also drops when idling, it sounds like either a water flow issue or an exhaust leak. The second case could be major. It could be a bad gasket or an actual crack that leys hot exhaust enter a water chamber.

 

[beatnick]

over heating

You could also take a look at the poppit valve.I just replaced my lower unit housing. It was corroded around the water pump and could not get a good seal. Some times it would work fine other times it over heated until finally it always over heated.Good luck I know what your going through!