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Yamaha 25MLHW cooling system

M

mic25

New member
I just replaced the water pump in this engine and water didn't come out of the pee hole, so I took the bottom end back off and found it was installed correctly. So I checked for clogs in the upper water system by using a hose and nozzle to put water pressure at the tube going up to the engine. Again no water came out of the pee hole. I removed the hose from the pee hole to the exhaust cover plate, it was clear. Is there a clog under the exhaust cover plate? Do I have to pull the cover plate and clean the passages out? What should I do next?
I am assuming there are no valves between the water pump and the pee hole, is this true? I did try to force water form the pee hole side hose down to the water pump pipe, but no water come through in this direction either.

Oh, another problem; the parts list shows there is a removable water elbow fitting at the exhaust cover plate, this isn't so. There is a post cast into the exhaust cover so the fitting isn't serviceable. It would have been nice if I could have removed this elbow and poked some weed eater line down inside to break up the jam. Any help on this matter would be greatly appreciated. This little Yamaha has been a gem.:(
 
Loction,profile? Salt or fresh water?? You might be close to someone who can help. Try compressed air in the fitting.Unfortunatly not all changes make it to the right parts diagrams. The old impeller was it chewed up,in pieces?The new torn up? Possible?You can take the thermo housing off and backflush the system?? Pictures always help.Serial#s,model#s year?
 
To clarify and update. This motor has been run in both salt and fresh water. Its a 1998.
I used compressed air. The old impeller had one broken vane so the stream was very weak. The weak stream caused the water pump concern and replacement. After reassembly no water came out of the pee hole, creating the further investigation. I'm pretty sure the new water pump is OK.
Since the posting, I pulled out the thermostat and used a hose to force water up the pump pipe. Water came up through the thermostat housing OK. I replaced the thermostat housing cover without the thermostat and tried again with the hose, still no flow from the pee hole fitting. I concluded the water passages under the exhaust cover must be plugged. So, I pulled off the electrical stuff and removed the exhaust cover. Things were very dirty inside but I found no obvious blockage. I cleaned everything out. There was enough stuff in the passages to create a problem though. I checked for water flow through the water passages and water came out the bottom OK. I think I have cleared whatever was clogging things up. Tomorrow I go to the shop and get new gaskets and reassembly will start.
By the way should I use permatex on the gaskets? What locktite should I use on the screws. After installing the exhaust cover I will check for flow through the pee hole before putting the electrical back on. If flow is OK I will reinstall the bottom end and start the engine as the acid test. If that doesn't work, I will have to redo the water pump.

Oh, this is not a fuel or carburetor problem, it's a cooling system problem.
 
I wondered whether I should have also pulled the cylinder head and cleaned out the cavities in there, but flow and temperature were so like new, I didn't. This motor is 14 years old but with low operating hours; maybe I should sell it. I hesitate because it has been so good to me over the time. What would you do?
 
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