Mercruiser 5.0 MPI Bravo 3 overheat 5 minutes after starting it up.

[Bravo402]

I got a 2003 Sea Ray 220 with a Mercruiser 5.0 MPI Bravo 3. The engine will overheat 5 minutes after starting it up. I have replaced the impeller and the back part of the raw water pump (where the hoses intake and out hoses go). I have replaced the thermostat as well. The first 5 minutes warming up the engine runs perfect. Then water temp starts climbing around 200. I shut it down before it gets any hotter. I noticed that the water hardly comes out the exhaust when this happens. While it’s still warming up water is coming out the exhaust like it should. I’m at a loss with this thing. I did touch the risers and they were not super hot like the thermostat housing was. Housing was hot as hell!

Serial Number for the engine is OM653566

Thank you guys for your help!

 

[dubs283]

check for blockage before and after the sea water pump. oil cooler(s) are known culprits for debris, blocked exhaust manifolds, exhaust flappers caught in y-pipe, etc...

did you find/remove pieces of the old impeller?

 

[Bravo402]

I didn’t find any blockages. The old impeller looked brand new. None of the pieces were missing off the old one. I replace it every year. Figured better safe than sorry. I’m going to check the flappers this afternoon. It seemed like it stopped getting water to the thermostat. Since the risers were still cool and thermostat housing was hot. Wondering if the circulating pump is bad? I hate to toss parts at it but this one got me confused.

 

[alldodge]

Do you have the 3 or 7 point drain system?
Have you looked at the check valve?

 

[Bravo402]

I haven’t looked into the check valve. I took it for granted I will check that as well. I got lazy thinking it either works or it’s doesn’t with the check valve. I need to look at the drain system again I can’t think off stop of my head as to which I have. I think it’s a 7 not sure. I can think of 4 places off top my head that have drain plugs. (2 on the raw water pump, 1 on thermostat housing, 1 on distribution valve)

 

[alldodge]

1 on distribution valve)

With a distribution valve you have the 3 point.
There are also check balls at the bottom of each exhaust manifold. If they stick open, then water is reduced going to the motor. Get a IR temp gun and take readings at different places to see where things are hot

 

[Bravo402]

Thanks brother. I’m on way to Home Depot to get a IR gun

 

[Bravo402]

I’m about to hook up hose and check with the IR. I took off the output of the raw water pump stuffed water hose down in the hose started taking off hoses one by one and have water coming out all hoses. Only one left to check is the hose that goes up to the T coupling from the distribution housing. Which I’m about to do now and see if it’s anything restricting it.

 

[alldodge]

The check balls

 

[Bravo402]

have good flow everywhere. Just checked new thermostat in water and it’s opening. Still overheating. I have no idea on this one.

 

[alldodge]

Need an IR temp gun to find out what is hot

Also install a short piece of clear hose (hardware store) where the water goes into the thermostat

Do you know if the check balls are closing off water going into the bottom of the manifolds?

 

[Bravo402]

Manifolds were reading 170, risers were colder than that could touch them. Thermostat housing was reading 200 on the IR

 

[Bravo402]

I believe so I just took the bottom hose off the check ball valve and had a ton of water in it.

 

[alldodge]

Then its the thermostat housing, the thermostat, Cir pump or those check balls.

Take the large hose off the Cir pump and serpentine belt off pulley. Then take a stiff wire and get it up inside where the vanes are on the pump. See if you can hold the pump vanes and still turn the pump pulley

I believe so I just took the bottom hose off the check ball valve and had a ton of water in it.

Those lines allow water to drain out but should stop water going up into the mans. Could try pinching off the lines going to the bottom of the check balls and see if things change.

 

[Bravo402]

One side had water coming out of the ball valve.
Went and did the other side no water came out of the valve. Not sure if that is cause when I did the port side it drained all the water out of the engine.

 

[Bravo402]

Thank you for all the help! I really appreciate it.

 

[alldodge]

If you connect the hose to the bottom of the check balls and water goes up and comes out past the ball, then it will keep water from going to the motor, and it will get to hot.

 

[Bravo402]

I will have to go to the store tomorrow when they open and get some hose and test the ball. Beginning to wonder if I got a blown head gasket at this point. I went ahead and ordered a new circulation pump. Took the old one possibly the original off and has a lot of pitting around where gaskets gone on the pump.

 

[Bravo402]

If you connect the hose to the bottom of the check balls and water goes up and comes out past the ball, then it will keep water from going to the motor, and it will get to hot.

Is it possible the manifolds and risers need replacing? The manifolds and risers are the originals that came with the boat I believe. Boat has never been in salt water. The original owner let the boat sit on the trailer for several years before I purchased it.

 

[Paintman1960]

Is it possible the manifolds and risers need replacing? The manifolds and risers are the originals that came with the boat I believe. Boat has never been in salt water. The original owner let the boat sit on the trailer for several years before I purchased it.

I'd be looking at them anyway before moving forward.
well over 15 yrs old ...
Michigan Motors has the stuff, If ya need them ,great folks