# Mercury 9.9 water pump irregularities



## drew7997 (Sep 3, 2012)

Hello all. 
I replaced my water pump impeller with a new merc part from the dealer. Replaced the lower unit gear oil. 
My issue is that the water now comes out irregular. It does flow continuous. But the "pressure" is different for the same RPM. 
see the video below and let me know your thoughts. 
http://s812.photobucket.com/user/drew7997/media/Fishin/20150503_184313_zpsuafaecjh.mp4.html


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## ohiojmj (Apr 16, 2004)

I had problem with pee stream strength on my 9.9 merc kicker and it was partial blockage from wasps or debris. I forced garden house water up its peeper and stream became strong again. This may not be your issue but thought I would offer it.


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## RushCreekAngler (Jan 19, 2011)

I had a similar problem on my 6hp 73 merc. There was a flush out plug on the side of the motor. Unscrewed it, hooked up the hose till I had a steady stream. No problems since


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## c. j. stone (Sep 24, 2006)

drew7997 said:


> Hello all.
> I replaced my water pump impeller with a new merc part from the dealer. Replaced the lower unit gear oil.
> My issue is that the water now comes out irregular. It does flow continuous. But the "pressure" is different for the same RPM.
> see the video below and let me know your thoughts.
> http://s812.photobucket.com/user/drew7997/media/Fishin/20150503_184313_zpsuafaecjh.mp4.html


I'd say totally normal. As the engine warms/heats up, the thermostat opens allowing the water to flow. As it cools down, the thermostat slowly starts to close, reducing the amount of water coming out of the engine. It will modulate open, partially, open, or closed based on the temp of the water flowing thru it. Again, good stream, totally operating as designed(mine does this exactly as yours is doing). The variable flow(modulation) is what it should do)! Nothing to be concerned with


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## steelneyes2 (Jul 19, 2011)

Above are all correct, the only other thing to be certain of is that when you installed the impeller you made sure all the vanes were properly swept back so they were rotating clockwise. As long as the indicator stream isn't hot, you're fine.


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## sherman51 (Apr 12, 2011)

take a piece of large weed eater line and feed it up the pee hole as far as it will go working it back and forth then remove the line. this will clean the hole if its stopped up. weed eater line is flexible and will feed right up the hole.


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## drew7997 (Sep 3, 2012)

I had no idea they had thermostats. I thought it was full forced water. I'd say it's running around 100* or so. It's very warm, but not skin burning. 
I'll take a thermometer with me next time out. 

I'll run the weekender string up, I checked the tube that comes off with LU, but it was clear. 

Thank you all!


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## blackxpress (Nov 20, 2009)

That doesn't look normal to me. Are you sure you got everything sealed up good when you replaced the impeller? A leaky gasket could cause it to lose water pressure.


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## drew7997 (Sep 3, 2012)

I mean, I suppose so. 
It was my first impeller replacement. However, I've rebuilt the top end of a 3.8l Chevy. So I'm pretty inclined. 
Where is the "gasket"?


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## waterfox (Dec 27, 2014)

I've done a lot of impeller replacements and on 10 hp
I always test them in a small bucket driven by a drill with a large chuck. You don't need a high rpm to make sure your repair
was ok. If your merc has a flush out plug remove it and a good steady stream should flow.


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## Rodbuster (Apr 14, 2004)

My 2011 9.9 has a hard stream as soon as I start it. My 150 takes 3 to 4 min to even get a dribble started


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## bountyhunter (Apr 28, 2004)

theres more than one gasket ,the one for the cover of the pump and the round one that goes around the shaft, and under the plate where the pump sits.


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## Marinette Sportfisherman (Apr 13, 2010)

Had this happen a lot with my smaller mercs. First pull the thermostat and run engine, if the stream is solid then its your thermostat open and closing but if the stream still is hard then gets weaker you have a vane of the impellar flipped. on the bigger like my 150 you have thermostats and poppet valves so it takes a while for 143f to open unless you rev the engine then the pressure open poppets for cooling. The small mercs are just thermostat 120f for restriction. buy a 130f melt stick and put on head and if it stays solid your good


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## drew7997 (Sep 3, 2012)

Anybody know where the thermostat is on this little guy?


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## Marinette Sportfisherman (Apr 13, 2010)

follow the tell tale hose from where it goes out the cowling now follow it back to where it meets metal and remove two bolts and its under that thermostat housing its small.


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