Bravo III overheat issues

[Nielsd]

Re: Bravo III overheat issues

Update:
Ok guys, get your Crayolas out and color me ignorant.

I finally got a moving blanket out to cushion my body and crawled out over the engine (not much room, even for skinny old me) and looked around. Took some doing. There IS NO oil cooler on this engine. I've been looking at a schematic for the wrong engine. Duh. The raw water goes from the P/S cooler to a unit called an 'accumulator' and then goes to the circulating pump with several other hoses involved. The accumulator is grey and black and plastic. I know what an accumulator is, but what does it do on this engine, how does it function, and what's in it? Could it be plugged? It's the next link in the raw water flow in this system. It sits down low on the port side of the engine, and I had to practically put my head in the bilge to see it. Of course. Education needed, please. I have searched several parts sites, I can see it in the pictures, but can't find it in the parts listings. I'm much more at home with an egg beater clamped to a transom. Had most of them, that's where I'm comfortable. Thanks.

 

[Fun Times]

Re: Bravo III overheat issues

Judging by your first description of you disconnected the hose going into the thermostat housing along with the two photos i would have never thought you had an Water Distribution Housing that looks like this, http://www.mercruiserparts.com/Show...681&bnbr=300&bdesc=Water+Distribution+Housing (AKA Accumulator Housing).

Your description sounded more like this water flow system,
http://www.mercruiserparts.com/Show...tandard+Cooling+System+(BRAVO)(7+Point+Drain)

Not this, http://www.mercruiserparts.com/Show...ling+System+(BRAVO)(Single+and+3+Point+Drain)

What does your thermostat housing look like? This, http://www.mercruiserparts.com/Show...0&bdesc=Thermostat+and+Housing(7+Point+Drain)

Or this, http://www.mercruiserparts.com/Show...rmostat+and+Housing(Single+and+3+Point+Drain)

Yes the water distribution/drain housing could clog up very easely.

What is your engine serial number? The boat year does not tell much.

 

[Nielsd]

Re: Bravo III overheat issues

Ok guys, finally got back to this thing. Life has been a little busy.
Yes, Fun Times, this: http://www.mercruiserparts.com/Show...rmostat+and+Housing(Single+and+3+Point+Drain)
is the thermostat housing I've got and this http://www.mercruiserparts.com/Show...ling+System+(BRAVO)(Single+and+3+Point+Drain)
appears to be the cooling system on my engine. I have verified that I have good flow right up to the Y fitting at the circulation pump. From what I can see, the only way for hot water to exit this engine is through the top of the thermostat housing and out the hoses going left and right to the exhaust manifolds. Is there an easy way to verify flow there? Can I safely run water through those hoses from a garden hose to see if there is flow? Or do I risk backing water into the engine somehow? Has anyone found the fittings at the manifolds be plugged in their travels? I DID remove the thermostat and do the boiling water test. The thermostat DOES open at about 155, but even at 190 it was not open as far as I would expect, given my experiences with thermostats I've seen in cars all these years. Suggestions?
Also, I have yet to be able to find the serial number on this engine, I know it's important. Can someone tell me EXACTLY where to find it? I've looked in the areas I've read about but still can't find it.
Thanks again.

 

[TilliamWe]

Re: Bravo III overheat issues

... From what I can see, the only way for hot water to exit this engine is through the top of the thermostat housing and out the hoses going left and right to the exhaust manifolds. Is there an easy way to verify flow there? Can I safely run water through those hoses from a garden hose to see if there is flow?...

Replace those hoses, temporarily, with clear hose would let you see the flow.

 

[Nielsd]

Re: Bravo III overheat issues

Replace those hoses, temporarily, with clear hose would let you see the flow.

Good suggestion. I was going to do that; I already have some hose and couplers to put a short section in and watch. I was hoping to do a quick 'garden hose' test on the manifolds themselves before I actually take it out and run it and see what happens.

 

[Nielsd]

Re: Bravo III overheat issues - FIXED!

Re: Bravo III overheat issues - FIXED!

It's been a month, I've been busy with other things, but the fix is in and I thought I should share what I learned. To start with, it WAS the manifolds. I finally was able to disconnect the appropriate water hoses and verify that I did indeed have good water flow through the engine. I used a clear piece of hose to temporarily view flow out of the t stat housing and came to the conclusion the manifolds HAD to be the problem. Here's what I saw when I took the elbows and risers off the manifolds:


Not too bad. Or so I thought. Note that this is the "closed cooling" manifold that has been used in recent years. The passages in the risers and elbows looked just as clear. Still feeling the problem was in the manifolds, I pulled them off and this is what I saw after taking the fittings off:


Turning the manifolds over and poking around, it was obvious they were completely plugged IN THE BOTTOM part. Also, when I pulled the port manifold off, there was still water sloshing around in it. My guess is that because this boat sat a bit in it's early years, the rot was down low after the water had partially drained out of the manifolds when stored.

I got a set of Osco manifolds and elbows, and was able to reuse the risers. The installation was easy, everything bolted up EXACTLY with no issues. I saved close to $500 by going that route vs OE. We took the boat out Sunday (finally!) and it ran a steady 161 at cruise, and 163 running wot.

Some interesting observations that may help others: 1: Water pressure is now around 7 psi at cruise vs 9 -10 with the old manifolds (before the overheating). My theory is that the higher backpressure was due to partially plugged passages. 2: the engine would run as much as 5 to 8 degrees warmer at higher engine rpms before as well: another sign of plugged manifolds, but a subtle one.

Hopefully my lesson and sharing it will help others. Thanks again for all the input and help.

 

[TilliamWe]

Re: Bravo III overheat issues

Glad you got it figured out. So glad you didn't spend a bunch of time and money to drill a hole in the bottom of your boat. And extremely glad you posted your results.

Good diagnosis (as opposed to parts changing) wins again!!!!

 

[Nielsd]

Re: Bravo III overheat issues

I agree on the hole drilling! That was one thing I really didn't want to do! On the iATN (automotive tech site) we were REQUIRED to post a fix or final outcome before we could post again. I got a lot of good insight from the responses here - they were all thoughtful.