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Goula Guy

Replacing water circulation pump on 5.0 Mercrusier in water

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Hi everyone,

i am wondering if someone else has had this problem.  I was running my boat over the weekend and the stb engine want to run warm during the trip (285-290 range/no alarm). I have checked the water inlets and the main water pump and all is good.  Do you think it’s the circulation pump on the engine that may be causing the issue?  And if so, can I change it with out pulling the boat?

Thanks to all!

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Need to know type of engine and outdrive.

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1 hour ago, Goula Guy said:

I was running my boat over the weekend and the stb engine want to run warm during the trip (285-290 range/no alarm).

Do you mean 185-190?  Because 285-290 would be cooked. It’s usually an impeller...

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7 hours ago, Goula Guy said:

Hi everyone,

i am wondering if someone else has had this problem.  I was running my boat over the weekend and the stb engine want to run warm during the trip (285-290 range/no alarm). I have checked the water inlets and the main water pump and all is good.  Do you think it’s the circulation pump on the engine that may be causing the issue?  And if so, can I change it with out pulling the boat?

Thanks to all!

The marine version of the engine coolant circulation pump has a stamped stainless steel impeller which is not a wear item. The only service item is the shaft seal and bearing set, and if either one of those items fail, you will see a water leak at the tell tale hole that is drilled into the pump snout, on the bottom of the bearing housing. Alarm should happen at 188, but not all helm displays are spot on. You may have failed the thermostat but likely it's the raw water pump impeller. Even a brand new impeller can fail in an instant if your out drive ingest some sand or you run over a trash bag which unfortunately is common in populated areas. You did not provide make, model, horsepower, and type of out drive so we can't comment further.  W

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Thanks everyone, and yes I did have a error in the range of temperatures that it’s reaching.  Range should have been 180 to 185.  I just pulled the impeller on the main water pump and it looked as good as the one I had bought to replace it with.   The motors are 2005 5.0 MPIs, serial numbers OWO36696 and OWO36695.   Is it possible that the thermostat is causing the problem and not opening fully?

Thanks!

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Could be a stuck thermostat but I doubt it.  How old are your exhaust manifolds/risers and elbows?  Also, though the impellers look fine - run the motor and then shut it off and immediately look under your water pump to see if you see water leaking.  If so, the seals are bad on your pump.  When this happened on mine it really wasn't leaking much when the engine was running which was weird but like I said, when I shut it off is when I noticed the leaking. 

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I have checked for leaks on the main and none are present. The manifolds and risers are original to the engines as far as I know(owned since 2011).  I had my service tech pull the risers and manifolds on the port engine last fall and all were fine and reinstalled.  I would assume the stb engine would be the same.  

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The first thing I check when there is to open the engine block drains to see if there is and sand or debris coming out of the drains. If there is,  I close them run the engine and check them again. There are times you ingest sand and it blocks part of the cooling system and hasn't done any harm to the impeller. It is also a quick, easy and free system check.

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