Mercruiser 5.0L / Bravo III overheats immediately :O

[mcginnal]

Hello all, I hope I might find some help on my broken boat! First, stats:

Boat: Monterey LS248 Bowrider
Engine: Mercruiser V8 (5.0L) (with seawater and circulating water pumps)
Drive: Bravo III

I am the second owner of this boat. When I bought the boat and launched it for the very first time, I encountered problems with the boat overheating. In idle, engine temperature would rise to 200F. A fellow boater looked at it, revved the engine for a few seconds, and temperature suddenly shot down to 150-160F. Problem solved..?

Fast forward to today:
Had the boat on the stand at the marina. Started her up, temperature was fine, etc. Launched the boat and pulled away from the pier. Gave it a little gas and suddenly, temperature started climbing to 200F! I backed off, put it in neutral, tried to rev it a bit, etc, but this time it didn't help.

After receiving a tow from TowUS FOR FREE (shameless plug- the membership paid for itself today), I put it back on the stand and put the muffs on to possibly flush it. This time, the engine wouldn't draw water, and no water whatsoever came out of the exhaust ports. Temperature still shot up, etc.

Here's the disturbing part, however: I pull the muffs off, and I notice something obstructing the exhaust port:

Piece of rubber that, to me, looks a bit too flimsy to be a seawater pump impeller blade. I could feel some more of it as I stuck my finger deeper into the exhaust port but couldn't pull it out. Would anyone be able to weigh in with some sage wisdom? I've pre-emptively started calling around to mechanics, as this doesn't look good. Thanks in advance.

-Alex

 

[Bondo]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

Ayuh,.... #1, Change the Impeller,...

#2, that appears to be a piece of a Shutter, which probably got burnt up before,...

 

[mcginnal]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

Ayuh,.... #1, Change the Impeller,...

#2, that appears to be a piece of a Shutter, which probably got burnt up before,...

Roger. #1 was my first hypothesis. What exactly is the "shutter", though?

 

[MarkSee]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

Item #7 in this link is the shutter that Bondo is referring to. Will want to get those replaced once all the pieces are removed as those help water from back-washing into the enigne.
EXHAUST SYSTEM-Performance Product Technologies

Mark

 

[Fun Times]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

Hi there Mcginnal, The part in your photo appears to be part of an exhaust water shutter that typically disintegrates with heat running through the exhaust system or the shutters can start to wear out with age. The water shutters will look like item number 7, [http://www.mercruiserparts.com/Show...4.png&inbr=2697&bnbr=250&bdesc=Exhaust+System

The first place to check for your overheat situation would be the sea water pump rubber impeller housing mounted to the lower starboard side of the engine block.

Hope it turns out good for you, Good luck.

 

[thumpar]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

I just had an overheat problem on my 5.7l with Bravo 1. It worked fine one day and 2 days later after 10 minutes at idle I got an alarm for overheat. The impeller had no fins left on it. Get the whole kit with impeller and housing.

 

[mcginnal]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

Thanks for the responses, gentlemen. I had no prior knowledge of exhaust water shutters (being so new & all to owning a boat), so I'm not so shocked at the pieces I pulled out of there. From what I've seen on videos, a seawater pump replacement looks challenging (i.e. space considerations) but not impossible. I guess I have my work cut out for me next weekend!

In regards to the shutter replacement, would anyone have experience in working exhaust manifolds? Is this a job that can be done with the engine still in the boat? Most videos/photos I've seen about this doesn't appear to be that way.

-Alex

 

[Bondo]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

Thanks for the responses, gentlemen. I had no prior knowledge of exhaust water shutters (being so new & all to owning a boat), so I'm not so shocked at the pieces I pulled out of there. From what I've seen on videos, a seawater pump replacement looks challenging (i.e. space considerations) but not impossible. I guess I have my work cut out for me next weekend!

In regards to the shutter replacement, would anyone have experience in working exhaust manifolds? Is this a job that can be done with the engine still in the boat? Most videos/photos I've seen about this doesn't appear to be that way.

-Alex

Ayuh,.... That depends entirely on the Boat, 'n how much of the boat can be removed to get at the exhaust,...

At a Minimum, ya gotta be able to remove the downturn elbows, 'n the rubber collars at each end,...

The Shutters reside at 'bout the lower rubber coupler,...

 

[thumpar]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

I am not sure how your boat is setup but what I did was remove the sundeck support rams and tilt it back. Then I removed the top support and the side support on the impeller side. Once I did that I had easy access. For me it was easier to remove the whole pump and reassemble off the boat. Now that I have done it I could do it in under an hour and plan to do it every other year or so.

 

[Fun Times]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

Also depending on year of the engine or style of the water shutters, you will want to ensure that you get all of the left over parts & pieces out of the y pipe / exhaust system as they can cause problems in the near future.

Some of the letter designed shutters have a metal rod that could lodge down inside the y pipe and wear a hole through the y pipe causing a water leak.

 

[mcginnal]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

I am not sure how your boat is setup but what I did was remove the sundeck support rams and tilt it back. Then I removed the top support and the side support on the impeller side. Once I did that I had easy access. For me it was easier to remove the whole pump and reassemble off the boat. Now that I have done it I could do it in under an hour and plan to do it every other year or so.

You are speaking of the engine hatch essentially, correct? That would make sense if so.

Also, I think I answered my own question about exhaust manifold removal after doing some snooping:

I guess there are shutters for each manifold, and then a single for the hull penetration. Ultimately, I'm confident that I can do the seawater pump on my own. I might look for some tech assist with the shutters and/or removing any FOD from the exhaust sytem.

 

[Bondo]

Re: Mercruiser 5.0L / Bravo III overheats immediately :O

I guess there are shutters for each manifold, and then a single for the hull penetration.

Nope,.... Only the 2 at the top of each leg of the Y-pipe,...

You'll need to pull the drive to dig out any remainin' pieces that Fun Times speaks of,...