1997 Mercury Jet Drive - Water Flow Problem

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jonboater65

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Sep 8, 2008
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1997 Mercury 40/30Jet 4 cyl. Model # 0G580758.

I am sending this question for a friend of mine.
He recently purchased a slightly used jet drive
jon boat. When he took it to the river for it's
maiden voyage the alarm came on that lets you
know that the water flow is not adequate for cooling. He shut it off immediately (he never allowed the motor to get too hot) then took it to a mechanic to have it checked.

The mechanic checked the motor and told him that mud daubbers had stopped up the motor from somewhere at the bottom and that this was restricting the water flow thus causing the alarm to come on. The mechanic attempted to fix the problem by removing the inspection plate and checking the water ports. He advised that he had flushed it out and installed a new impeller. Upon the second run it ran fine at first while it was cool but when it started heating up it began to only spit water and vapor and not have good flow.

My friend is at wits end. He removed the lower unit and hooked a water hose to it and the flow is fine. However, once the unit is reinstalled it spits after it gets warm and does not have enough flow to keep the motor cool. Does anyone know what may be stopping it up and how to unstop it? Does the water only flow around the jugs or is there a passage for it to flow around the crank area and does this motor have any type of thermostat? Any advice on how to flush the motor to see if there is any other obstruction? Please if anyone can help it would be greatly appreciated.
 

bstuart

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May 5, 2020
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Did you guys ever figure this out? I'm having a similar problem with a prop Mercury 40 HP.
 
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