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2004 merc 350 mag mpi high temps on new dry joint manifolds, one thing after another with this boat

Also watched your vids, I have a couple of suggestions:
1) it is much better for the impeller to use proper muffs, than to run it in a trough as you are doing in the vids. An inboard impeller set up is not designed to pull water up into the drive, it is designed to work with water filling the drive water passages and raw water intake hose all the way up to the impeller. With the boat in the water hydrostatic pressure will fill the hose all the way up to the impeller. The way you are doing it is likely to suck in air which tends to wear the impeller faster than normal. The muffs will come close to filling the hose, if they fit right.
2) it is best to run it at idle, even with good muffs, the water hose cannot supply enough water to keep both the engine and exhaust cool, at those elevated rpms. Limit rpm on the water hose to about 1200 rpm

the best muffs I've uses are the MerCruiser/Quicksilver round ones with the metal clamp, some of the dual inlet rectangular ones are made of rubber that is too stiff to conform to the shape of the lower unit.....
The muffs below are the ones I used in my vid above.
 

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it is unlikely you get water/gases out of the prop due to he bravos using exhaust tubes instead of bellows. most water and exhaust escape before the leg. the water flow is great out of the back of the boat and the flow coming to the manifolds look real good as well, that is without the thermostat? correct?
 
louc said:
Also watched your vids, I have a couple of suggestions:
1) it is much better for the impeller to use proper muffs, than to run it in a trough as you are doing in the vids. An inboard impeller set up is not designed to pull water up into the drive, it is designed to work with water filling the drive water passages and raw water intake hose all the way up to the impeller. With the boat in the water hydrostatic pressure will fill the hose all the way up to the impeller. The way you are doing it is likely to suck in air which tends to wear the impeller faster than normal. The muffs will come close to filling the hose, if they fit right.
2) it is best to run it at idle, even with good muffs, the water hose cannot supply enough water to keep both the engine and exhaust cool, at those elevated rpms. Limit rpm on the water hose to about 1200 rpm

the best muffs I've uses are the MerCruiser/Quicksilver round ones with the metal clamp, some of the dual inlet rectangular ones are made of rubber that is too stiff to conform to the shape of the lower unit.....
The muffs below are the ones I used in my vid above.
Click to expand...
Hi, thank you!
I do normally use muffs esp. when flushing the system with antifreeze. how ever, i wanted to check on the capacity of the impeller/for a proper outflow, as you mentioned, the muffs will only suffice for idling, but not much more, that´s why i tested it this way.
 
stang32 said:
it is unlikely you get water/gases out of the prop due to he bravos using exhaust tubes instead of bellows. most water and exhaust escape before the leg. the water flow is great out of the back of the boat and the flow coming to the manifolds look real good as well, that is without the thermostat? correct?
Click to expand...
Hi stang32, thank you for your reply! yes, this is without -t-stat...
just like in good parts of the US, Winter is back in Austria too, so testing it on the lake is not an option right now.
What I have found out though: new / replacement risers have a water-flow-connection between the front and and rear "ports" thus cooling the riser´s middle too and allowing for a better flow since the front port has the restricted -flow gaskets.
How ever, if that was the issue, the issue should have been here from the start...or in other words: risers getting very hot in the middle (btw. front and rear) should sort of be normal (if there is no water cooling the metal?!)
of course i´d prefer to not spend another K, but if that is what will prevent another manifold from cracking...
 
Hi, may I ask why. As far as i understand water is pushed up from the joint's second tube which is sort of directly linked to the impeller outflow. Or am i wrong? Thank you for your thoughts
 
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