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Trouble shoot impellor and cooling question.

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Trouble shoot impellor and cooling question.

Old 11-27-2014, 04:21 PM
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Default Trouble shoot impellor and cooling question.

The boat - 2005 Mercury 115 four stroke saltwater series.

The story - Had the boat next to some heavy vegetation this morning on the lake. Before making my way across the open lake (no more vegetation) I know for sure my engine was cooling (peeing from motor). I get more then half way to boat ramp (aprox. 10 minutes of running); and the motor alarm goes off. I immediately recognize motor is no longer peeing. I try throttling up to force pressure with no avail. Took apart cooling line and blew in it, could blow water out the exhaust port and could hear air coming out the pick up on foot. Came home and dropped the lower unit, pulled the impeller. Here is what I got...

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The impeller had no major debris I could see with the naked eye, but the research I've done says an impeller that looks like the one above should be replaced. So, I don't think I solved my problem, but should I go ahead and replace the impeller?

Now the seal below it DID have some grass and other vegetation (aporx. 1.5 inches long) in the impeller housing. I know that's bad, but I don't believe that was my problem.

With this being said... Whats my next step? I'm looking for the schematic that shows the cooling tube when it enters the lower unit... I'm a little lost how the route of water makes it from the pick up, to the impeller, to the cooling line...


any help is appreciated!
Old 11-27-2014, 04:48 PM
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Back flush it from the thermostat hole and the flush port with the foot off and put it back together,. There is nothing wrong with that impeller but since you have it in your hand you can replace it if it makes you feel better..
Cut a little piece off your kid's swim noodle and slip it over the end of the hose to make a good seal to the thermostat port.If you use one of those hose end shut offs, you don't get as wet. It is also good for the ear muffs.

Old 11-27-2014, 05:51 PM
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Never only replace the impeller, I always replace the whole water pump unit as one. The base plate gets groved by the impeller and then won't make as much pressure as it did before. Not always the case but in my opinion you already have the lower unit off why not change it. It can cause problems if both the housing and the base plate have wear.
Old 11-27-2014, 08:45 PM
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Thanks for the replies guys. Got her fixed and tested it tonight. The hose coming off the exhaust side was caked with grass. I blew it out and buttoned everything back. Went to the boat ramp and ran it for 15 minutes up and down the channel. Tell tale was peeing like a champ!

Thanks again folks.
Old 11-28-2014, 08:45 AM
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There is no way to guess the health of the impeller while it is still in the housing. I've broken down water pumps before that looked great until I pulled the impeller from the water pump housing.

If, when the impeller is out of the housing, any of the arms of the star stay bent, replace it. It is the tension of the arms trying to straighten out that does the pumping. If one or more stay bent, then your down that much pumping effect.

As a matter of fact, as mentioned above, if you have it apart, replace it.
Old 11-28-2014, 09:15 AM
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If you take a good look at that impeller and wear plate, both appear to have wear (plate is grooved, impeller is worn around the center hole).
Old 11-28-2014, 09:37 AM
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Originally Posted by LouC View Post
If you take a good look at that impeller and wear plate, both appear to have wear (plate is grooved, impeller is worn around the center hole).
That's why I suggested replacing the whole pump.

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