Mercury 25HP 4 Stroke 1999 No Water Flow From Pump To Power Head - Tell Tail

[darren.m]

I'm in need of desperate help. My 25HP 4 stroke Mercury Mariner is not pumping water. I have changed the water pump, thermostat and have now taken the cylinder head off. Everything seems OK except I am getting no water from the water tube to the power head. I have taken the lower unit off again and put a garden hose pipe on the water tube. I have taken the cover / thermostat housing off the side of the power head which gives good visual access to water ways and exhaust ways. When I turn the water on to the garden hose you can hear a gurgling and see air bubbles being push out of the base on the power head where the water should come up into the side of the power head before being sent off to the cylinder head etc. Once the air has escaped virtually no water flows. if I take the garden hose off the water tube the water does not flow back to the bottom of the water tube. There has to be a blockage of some kind between the top of the water tube and in the adapter plate where the power head all bolt together. I was hoping there may have been an accessible poppet valve but I can see nothing. I can push a piece of insulated wire up the water tube to about the length where the tube disappears into the adapter plate. Going the other way I can get the same wire from the water port just above the power head flange / gasket down to near where you would expect the water tube to enter the adapter plate but no water flows. I'm not sure of the configuration of the water ways etc within the adapter plate so this is where I am now stuck. Do you have any ideas???. I have posted a short video on Youtube to show my efforts, You can see the general arrangement of the engine and where the water is gurgling up into the power head. Thanks for your interest. Darren. Youtube link http://youtu.be/c3RHH3z2_jg

 

[spannerman]

Sounds like the classic salt problem, we have seen a lot of outboards with this problem. There is a rubber ring to seal where the water tube crosses over between the block and the adapter plate, over time salt crystals builds up behind the rubber seal collapsing it inwards until it strangles the water flow, you need to remove the block from the stem, a good cleanup and new seal cures it.

 

[darren.m]

Hi Spannerman. Thanks for the reply. Would I get away with trying to put some Fernox etc through to clear the salts? I did read somewhere that there was also a problem with dis-similar metals used on the gasket which caused the seal to squash up like a sphincter!! , have you heard of this? Thanks

 

[spannerman]

This is what has happened I think, either a gasket problem or salt crystals, the only sure way is to split the motor and clean all the galleries and replace the gasket/sealing ring.