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87 9.9 Mariner water problems

dennisschuldt

New member
I have an 87 9.9 that runs fine at low to medium speeds. When I go to wide open throttle, it will run fine for about a minute or two, then it will start to overheat and no water comes out of the pee hole. As soon as I back off the throttle, it will start to pee again. When I bought the motor, the impeller was not working and I replaced it. I'm not sure if there is a blockage somewhere that only plugs when at full throttle. I pulled the thermostat and did not replace it. There was a little debris in the cavity that I pulled out. What should I try next to clear any blockage that might be in there?
 
I too had a LOT of trouble messing with one of those. In fact, I gave up and handed the fool thing back to the customer without even charging him.

I've since learned there are two washer deals that go above and below the impeller to seal it. Without these washers, the pump lacks sufficient vacuum to pull water in. The impeller on these is centrifugal in design (vs. positive pressure for other impellers). This is what causes the problem since--if you've ever messing with swimming pool pumps--you know how hard it can be to get one pumping; the tiniest air leak, or air pocket inside, causes them to refuse to pump.

Jeff
 
I am going to drop the lower unit and go through the pump again and will look for the washers like you said. I will also try and look for some debris I might have missed. I pulled the hose from the side of the block that goes to the pee hole. It seems clear, Not sure what is under the cover where the hose connects to the block. Any ideas that this might be blocked at higher speeds? I'm ready to go buy a new 20 hp Merc and be done with this one if I can't figure it out.
 
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