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Old 07-23-2008, 07:43 PM   #1
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Default 2003 Mercury 90 HP Water pump

I need to replace the water pump on 90 HP 2003 Mercury Saltwater 2 stroke.Do I put the shift on forward or neutral.Also is there any thing else I need to look for?I know to remove the 4 nuts and the bolt under the trim tab.Is there anything I need to do with the shift in the lower unit?The motor sucked up alot of sand and since pump flow is low at the pee hole.I flushed the motor after with the flush hose on the engine but still very low flow.I was thinking of trying this with the boat in the water with the engine tilted all the way up and working from a floating dock.Is there anything that could easily drop into the water when I try to remove the lower unit?Thanks
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Old 07-23-2008, 09:08 PM   #2
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Default RE: 2003 Mercury 90 HP Water pump

I've changed my water pump out on my old 1987 90 hp Merc numerous times and would never think of doing it while the motor was in or over water.

I always leave my motor in neutral when changing the WP. The key is not to change the position of the lower unit gear shifter. Come to think of it, there is a type of splined bushing that sits on top of the lower unit, that connects the gear shifter. As it just sits on top of the lower unit (when the lower unit is removed), it could easily dropped overboard. Same thing goes for the water tube seal which connects the water tube to the top of the wp housing.

Not sure if your '03 would be any different than my old motor.
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Old 07-24-2008, 03:52 AM   #3
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Default Re: 2003 Mercury 90 HP Water pump

I would not do it in the water your just asking for trouble. Leave it in neutral. Replacement should be pretty straight forward. Sometimes the lower unit is stuck after you unbolt it and you have to gently hit it off or pull it off. If it releases when your not expecting it it will get a little awkward and you could drop in in the lake, not to mention all the bolts and nuts and stuff.
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Old 07-24-2008, 03:28 PM   #4
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Default Re: 2003 Mercury 90 HP Water pump

Do not remove or work on the gearcase over the water. Parts and tools do not float.

Pull the gearcase in neutral. Use compressed air to blow back through the water tube to clear out any sand in the system. Pull the thermostat and clean out that cavity also.
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Old 07-24-2008, 04:01 PM   #5
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Default Re: 2003 Mercury 90 HP Water pump

Thanks for the replys,I guess I have to haul the boat.I was figuring that until someone I know suggested doing it in the water.Bad idea
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Old 07-29-2008, 05:35 AM   #6
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Default RE: 2003 Mercury 90 HP Water pump

OK,I got the lower unit off.Does it matter which direction the new impeller goes on?I figure after starting it will set itself to the correct way,Is this correct?I put some marine grease inside the pump assembly as per the advise of the dealer I bought the pump from.Is that correct?I also got a new thermostat for it.Any thing else I need to look for???Thanks
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Old 07-29-2008, 05:39 AM   #7
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Default Re: 2003 Mercury 90 HP Water pump

Alos one more question.I am going to change the lower unit oil.There 2 upper plugs.one says vent.When I fill it which plug do I remove to make sure it is full.Any other outboard I have done just has one upper and a drain,I have always filled from the bottom to the oil comes out the top.thenks
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Old 07-29-2008, 06:27 AM   #8
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Default Re: 2003 Mercury 90 HP Water pump

Vent
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Old 08-01-2008, 07:19 PM   #9
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Default Re: 2003 Mercury 90 HP Water pump

all done,all is well.We just got this boat,it seems to idle a bit rough.It looks like the carbs are adjustable.Should I try to adjust them to see if it gets better or leave it alone?Is there a special procedure to adjust them?Thanks
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