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Random Quote: Neccessity is the Mother of invention. Hunger is the Father.
Ok some may remember me posting about my 5.7 i/o not having as much water coming out of one exhaust vs, the other. Anyway pulled the manifold and elbow(no riser), after inspection they appeared to be good. also I checked the exhaust flapper.
So this am I decided to put boat back on lift. Ran the boat at home, ran fine went to 175 deg and stayed which is normal. Launched boat and ran toward the house, got to the house and the boat started to overheat.
Get boat on lift and check to see if water is flowing through exhaust(checking impeller) it is, but only good on one side, the other side is blowing steam and very little water?
What else could it be, I check mainfolds, elbow, hoses, flapper?
I will offer what I can...I am not that knowledgeable with cooling system on inboards. Outboards, yes, I can work on them all day long, had one recently that sat for years, no water output after installing new water pump & T-STAT. Pulled the head & found MAJOR blockage in water passages around the lower cylinder.
Anyway. Is this a raw water pick up? Have you checked the possibility of a blockage on the side that water is not coming out of? How about if there is rust that has flaked off & blocked the flow? Is the T-stat opening ALL the way? How good is the impeller?
Running the boat on the lift is not the same as running at speed in the water. Could still be a bad impeller. That's about all I have to offer, not much, I know. I'm sure someone with a lot more knowledge will come along & hit the nail on the head. GOOD LUCK!
Raw water pickup, I guess something could be blocking it, as a little water flows through on that side, but not much. I guess new manifold and elbow are what I need next?
Which out drive? Bravo or Alpha. I have to assume you started with the simple stuff, like replacing the impeller. Does the boat have closed cooling or raw water cooling?
Jay
did ya make sure there is no air leak at the pump or strainer....i chased a gremlin for 3 weeks...to finally discover the faulty gasket on the strainer...
I have checked impeller, mainfold, elbow, hoses, flapper. It is a raw water system. Water does not flow on one side hardly at all. I guess I could replace the manifold and elbow, but that is $500 of guessing.
I may call in a mechanic, it would be worth someone figuring out exactley what it is as I have spent probably 25 hours or so trying to figure it out, and obviously I have no idea what the hell I am doing.
replace the impeller but while the system is open, back flush it as hard as you can with a hose. Remove and look into as many cooling hoses as you can, are there salt deposits or scaling? If you've had the exhaust off the motor, what did the insides look like? If OK, you should be able to install new gaskets on the existing manifolds.
You still didn't say if it was a Bravo or Alpha drive? The reason I asked is that on the Alpha's the intake hose runs from the top of the drive through the transom assembly. There is a built in aluminum nipple that passes through the transom. This can become clogged by corrosion, gunk, sealife etc. You may need to try to clear this. Finding the end of the the hose were it attaches to the motor and backflushing it is a good way to start.
Jay
If you don't wan't to spend the money on a new manifold you could have yours bead blasted. I think most radiator shops can do this. Its like sand blasting but with some type of beeds and if I'm correct they can also tell if anything is blocking up the manifold.
I would try and replace the engine mounted water pump if that doesnt solve the issue you may have a blockage somewhere thats what happened to my friend 5.0 mercruiser he had a built up of salt deposits somewhere which restricted the flow of water
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T500, please tell me more, I don't know what that is?
So that I can look up the diagram of your motor and direct you to the right location......is this a Mercruiser engine? What year? 5.7 with a BIII correct? and it shouldn't matter, but what boat?
Mercruiserparts.com has parts diagrams of nearly every I/O motor made......best way to look up what you have is with the serial number. (I'm very familiar with their 500+hp motors, just not the small blocks)
Thanks t500, I have the shop book I will look it up and see what it says.
You said you checked the impeller and if the Bravo III is like the Bravo II (which I think it is) you would have allready pulled the raw water pump if you checked the impeller. The pump is not in the lower unit.
ok then it was checked because the impeller is on the front bottom of the engine.
the thing is port side water is flowing just fine, only the starboard side, so there must be a blockage somewhere.
Yes then you did check the impeller. That motoer has the raw water impeller you checked then the water pump like in a car which maybe that getting weak but if you have good water flow on one side its sounds like blockage. Did you see my post on having the starboard side manifold bead blasted? Its pretty cheap and if I'm corect they can also tell if the manifold has blockage.
You need to start at the thru hull. This is why I asked Bravo or Alpha. The Bravo drives typically have a thru hull fitting with a valve that draws water in just like an inboard boat. Follow the hose from the water pump, belt driven on the front of the motor that has the impeller in it, down to the bottom of the boat. Check the valve does it turn on and off easy? If it is blocked with marine growth or corrosion it will be hard to turn on or off. Check to see if there is a strainer in this line, if so close the valve open the strainer and clean it out. Now with the strainer open, open the valve and see if water comes in. If it doesn't the thru hull is clogged if it does the problem is upstream. As for the pump and impeller, who checked it? Did they grease it when they reinstalled it. It is very easy to burn up even a new one if it isn't properly lubed up and you run it dry for any period of time. I usually pack them full of grease and dishwashing soap. The soap will bubble up in the exhaust when the motor starts if you are pumping water.
The discharge cooling water goes to both manifolds equally. If there is more resistance in the discharge lines on one side, more/all the water will go to the OTHER side. It's not unusual for one side to cool better than the other. Find/remove the restriction, or CREATE more restriction on the cool side to force more water through the restricted side. It's often as simple as a kinked hose, or one hose longer than the other.
Help - I/O 5.7 Overheating - Part Deux 
