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FieldServiceTech, Mechanic
Category: Boat
Satisfied Customers: 147
Experience:  19 years boating and outboard motor experience
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Water pump for 50 HP Mercury outboard is out. How to verify?

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I have a 50 HP 2 stroke Mercury outboard. I believe the water pump is out but not positive. Are there any sure signs I might be right?
Hello and thanks for using justanswer.
From the information you have provided, I can say with a fair amount of certainty that your water pump impeller is bad. Your tell-tale stream is your best indicator that your pump is working properly. If your engine is overheating and there is no water coming from the tell-tale, your impeller should be the first place to look.
You should change your impeller every 2-3 years.
To change your impeller, just follow the steps below.
Step 1: Make sure the motor is shifted to NEUTRAL
Step 2: Tilt the motor all the way up (it will be easier to remove the lower unit like this and will prevent it from just falling on the ground)
Step 3: Remove the trim tab (mark it's position so you can install it in the same spot)
Step 4: Remove the bolt that is located inside the trim tab cavity
Step 5: Loosen the mounting nuts (or bolts) that mount the lower unit to the midsection. Do not remove the nuts completely, but loosen them all the way.
The lower unit is now free to come off. When the lower unit is loose and falls down to the loosened mounting nuts, you can take the nuts off.
Drop the lower unit just enough to remove the small plastic tube from the front of the lower unit. This tube supplies water to your speedometer.
Step 6: With the lower unit removed, you can see the water pump housing. Remove the hardware holding the housing on and lift the housing. Under the housing, you'll find the impeller.
Remember when installing a new impeller to twist the impeller into the pump housing and ensure that the fins ‘curve' in the same direction as the old impeller.
Remember to re-install the square key back into the drive shaft and impeller if it has fallen out.
Assemble the pump and lower unit in the reverse order of disassembly.
That's it. You've just successfully replaced you impeller.
Hope this helped
Customer: replied 8 years ago.
It sounds simple enough but I am a first timer and a little intimidated. I am a semi-professional DIYer and I am sure I can do it. But might you have any illustrations? If not I ordered a service manual and it should explain how to do it just like you said but it will take almost a week to get it. So any additional illustrations or photos would help me immensely and make the job go smoother.
I was also wondering if you know of any good places on the web to order parts. We only have one boat shop in town and everything takes a week to get.
Absolutely, follow the link below to your parts. This is a great place to order parts from and it will show you an illustrated parts breakdown of your lower unit and pump. Click the link, then find your motor by horsepower, then click your engine serial number. What you are looking for next is a link to your gearbox (driveshaft) section. It will show you exactly what you need.
Hope this helps
FieldServiceTech and 2 other Boat Specialists are ready to help you
Customer: replied 8 years ago.
Thank you
Here's a step-by-step with photos

Customer: replied 8 years ago.
I have everything apart and the directions you sent me are awesome. It was so easy. So I went to the website you recommended for parts and tried finding what I need but my serial number does not match any of those listed. The serial number I got off the tag on the motor is(###) ###-#### Can you get any information from that?
Here's the link to your serial number. I found it under the link for 50 (4cyl), serial range(###) ###-####and up.

And here is the direct link to your lower unit and water pump...

Take care

FieldServiceTech and 2 other Boat Specialists are ready to help you
Customer: replied 8 years ago.
I was able to make it to the local boat guy and to my surprise he had a full kit on hand. Usually no one ever stocks anything in this area. So I was able to get everything together and working today. I don't know what I would have done with out finding this website and you be so willing to help. Thank you.