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Mercruiser 5.0 cooling hose swelling into serpentine belt

Assuming this is the big J shaped hose between water pump on block and thermostat housing ?you have a down stream restriction which is causing it to swell check that manifolds risers and elbows are clear so warm water can get out of engine
 
I plan on letting it idle with the water muff and see if one of the manifolds is hotter than the other. I may also check the water pump for blockage
 
MrJanx said:
Any idea how easy it is to remove an elbow? I have a scope that I can put in there and look around
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very easy - biggest pain is to scrape off old gasket. spend the money for the OEM metallic gray ones

you will not need a scope once you get the elbow off you will be able to see how much scale is in there. Does the engine over heat ? Salt or fresh water
 
Found out these are the original manifolds and risers from 2003. Prior to last year boat was kept inside a boatel and only used once a year.
 
I'm wondering if just taking off the large elbow at the rear would allow me to see if there is any nonsense inside before I take the whole thing apart.
 
If it was used in salt water that long even with low hours the elbows will corrode like crazy because water drains out of them, so salt water + air = maximum corrosion. I'd get prepared to replace that whole exhaust system. The other risk besides overheating is if the exhaust rusts through you will wind up with salt water in a cylinder and a ruined engine. And you won't know, till the starter goes CLUNK and it is seized up from rust or hydrolocked.
this is my old OMC batwings after 5.5 seasons in salt, one of the outputs was totally clogged. The longest I ever used them was 6 seasons, and never had a rust through putting salt water in the engine, or an overheat from clogged exhaust. I went though 3 sets of these and then when I had to do the last replacement these were long since NLA so I converted over to the later 2 piece style.
 

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I've had good luck with Barr marine, they do make the Merc dry joint. With the dry joint while you don't have the risk of a leak at the old style wet joint interface, if the elbow or manifold rots through, you got water in a cyl. So dry joint is an improvement, but it does not eliminate the need to replace exhaust components when needed.
Those OMC batwings didn't have a joint that could leak into the engine but if they rusted through you are in the same place.
I tried rodding out that old pair before I changed them and I could see the wall thickness of cast iron was getting quite thin. So, to the metal re-cyclers' they went!
 
Had the risers and manifolds replaced. When the mechanic took it for a water test the hose swelled again and was cut by belt. This is from the mechanic.

We performed the Thermostat service , mended the hose , reinstalled and tested on the river with Dianostics equipment. Unfortunately there is way too much much water pressure. Should be around 1 lb at idle and up to 12 at top speed. You’re at 16 at idle and 25 if the boat is reved up sitting still.
 
This doesn't just happen over night. Something has been building for a long time and now it's gotten so bad that everything upstream is getting backed up. The pump on the front of the engine is a circulating pump that is to say it has no ability to suck up seawater, or create pressure. The seawater pump is responsible for providing cooling water to the engine and it is the pump that pushes it through the engine and out the risers. I fear this may be time to pay Big Bill and have the engine out, heads off and check all the water passages for rust.
 
that's a pretty big pressure delta for an 'open' system....which suggests a helluva restriction or a big pressure boost...
 
makomark said:
any idea where they made the pressure measurement?
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That's a good question. Would seem there is a down stream blockage or (admittedly grabbing at straws) a high volume water pump was installed or maybe wrong water pump pulley driving it faster?
 
Stupid question, but is that a new hose or one that's been there for a while? Just wondering if the hose walls are separated and it's ballooning?
 
Both, the one that got cut when I had it out could have been old but didn't look bad. New one was put on and did the same thing when boat was put on plane
 
When the thermostat is closed when engine is cold, the engine water pump circulates water in the engine through pump body,
Once thermostat opens due to block water temp increase, the cold water being supplied to T stat housing is mixed with block water and the Tstat maintains temp.

As others have pointed out, its either the block water flow is being reduced due to crud and or corrosion.
I would think if exhaust manifolds or elbows had water flow problems the block temp would rise above 150* in short order.

Whar else mat be happening is based on where temp sensor is, that area is maintaining temp.

Do you know what temp the fhermostat is? 140 or 160 ?

Typically a 140* Tstat will give you ~ 160* at guage. A 160* Tstat will give you ~170-180* at gauge.

So a temp gauge reading of 140* may be a bit cool which may be one indicator of an issue. Again it also depends on temp sensor location to funderstand more.
 
Did you happen to notice the hose during the "30 min test"??

Not trying to pick but to understand what is known about when the root cause came about....like o2batsea suggested, this stuff usually doesn't happen overnight...
 
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