Engine overheat and water leak at top of y-pipe

[badinfluencect]

1989 Mercruiser 260hp fresh water cooled on 26 Carver. I just completed a gimbal housing replacement. Replaced the following:

Complete gimbal housing n gasket
All bellows
shift cable
y-pipe n gasket
flappers
exhaust manifolds n gaskets
risers n gaskets

Tested boat by running with garden hose into raw water pump for 15 minutes. Ran fine stayed just over 120 degrees. When i put the boat in the water and started i noticed small leaks around the rubber boot that attaches to the y-pipe. Hose clamps were tight but i socked them even tighter. Leak went away. Boat idled out ok but started getting hot as soon as I started throttling up. I also noticed she would not throttle up as normal. Would bog out at around 2k rpm. Idled her back She got up to about 220 degrees. I ordered a raw water pump impeller because that is one part i did not replace. Because of the bogging issue however, I don't think that the impeller is the issue. I feel like the water leak from the y-pipe is a symptom. I believe i installed the flappers correctly but i am wondering if having them installed backwards would create the symptoms I have described. I am planning on pulling the boots off and looking in to inspect flappers when I get to the boat this weekend. Hoping someone with some expertise on here can share their thoughts on whether or not flappers can cause what I have described. Also welcome any other thoughts.

Thanks in advance.

 

[alldodge]

Leaking on the exhaust side will have nothing to do with overheating, it just puts water in the boat. The impeller would be the first thing that could cause it

Flappers are installed pointing down. This allows water to pass easy and spring back in place if water tries to flow back toward the motor

Is one of these your cooling setup?

 

[badinfluencect]

alldodge... this is how my cooling system is designed (attached)

 

[alldodge]

Thanks, closed cool full system with rear Heat exchanger, and Inboard

I understand further about the flappers your talking about, there not in the exhaust, they are exterior on the outside of the hull, correct?

Having an inboard most have water mufflers which are inside the boat

 

[badinfluencect]

Sorry. That is the wrong picture. I can't find a pic that represents what I have. I have a mercruiser 260 with a fresh water cooling system. There is a heat exchanger near the bulkhead and a y-pipe that bolts to the gimbal housing. At the top of the y-pipe there are flappers. I was able to verify today that the flappers are installed correctly and the raw water pump impeller was fine. Next I am going to replace the thermostat. I will report back after I test that fix. Thanks for yoyr help.

 

[alldodge]

Many times with the older motors overheating with closed cooling is the HE. Have the end caps been removed to check the tubes?

 

[badinfluencect]

Thanks. I will check that when I replace the thermostat.

 

[vetting]

Did you own the boat before this work was done?

For the bogging at 2k rpms.
Check timing.
Check your distributor cap - make sure the metal is all clean on the underside.
Could be a carb issue.
The one I've seen most on boats that were docked in the water is the checkvalve and other crud in the gas vent line running to the tank. Spiders love making a home in there. This motor will bog like crazy at higher RPMs since its a engine mounted pump that is sucking gas to the motor instead of like on a car where its pumping it from the tank. When its trying to pull gas in from the tank and the vent is clogged, it creates a vacuum in the tank and it cant pull the gas fast enough.

 

[badinfluencect]

Thanks for all the help alldodge and vetting. I went through all the items in your lists. I ended up replacing every part in the cooling system except the water pump attached to the engine. In the end it was stupid user error. I would test it on land with a hose feeding the raw water. I let it run for up to a half hour and thought i had it to the point where the thermo opened. When I put it in the water, under load the thermo actually opened and the coolant which was full to the brim would dissapear and the engine would get hot. It was just air in the system. Once i refilled the coolant to the top she is hanging in at normal temp 160 to 170. The water leak at the top of the y pipe was old rubber. I replaced those and that fixed that. I still need to time the engine but my major headaches are done. Thanks again for your help