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Water Pump Base on 15 hp Merc

M

mlmarkee

New member
A few days ago I asked about dropping the lower unit to get at the water pump on my 15 horse merc. The serial number is 0A743570 Model number 1015201GC 1989 MERCURY CANADA 15 M. Well, as you can guess...I have another question. The impeller is not too bad on it, but since I have it apart I am going to replace the impeller, but what seems to be the main problem is the seal sticking up out of the top cover assembly above the impeller. In the process, I was noticing from parts schematics that there are 2 designs of the water pump base under the impeller. Is there any way to figure out which water pump base design I have without removing the water pump base to see the underside where they look different? The seal around the driveshaft looks good, so I really don't want to open that up just to look at the underside. Any ideas where I could find this out? Thanks in advance.
 
No you can't tell until you have it pulled but it's only the base that's different - all the other parts and seals are the same.

Replace your impeller and I would replace that funky o-ring that presses into that little channel in the bottom of the cover.

Also the little rubber inset in the cover (where the drive shaft goes through and the stem for the water tube). It simply presses into the the cover. Often a crack in the rubber develops between the hole for the drive shaft and the water tube. You need to pull it from the cover and (distort) it to see if it's cracked or not - if so, replace it...

Unless you have water intrusion into the lower unit I almost never fiddle with waterpump base on the 6/8/9.9/15 horse models...
 
Yes, the main culprit seems to be that rubber stem piece on the top of the cover--it is cracking at the bottom of the stem and it also looks worn where the driveshaft comes up through.
Which funky o ring are you talking about? I am having trouble figuring out which one that is.
Thanks again for the help.
 
Sorry, o-ring is on an OMC waterpump - I'm getting old and senile :)

Ok, little Mercs = that rubber stem/seal and any gaskets between the cover and the base.

No need to pull the base up...
 
Thanks--that is no problem. With as much stuff as you know about these motors I don't know how you would keep it all straight!
I just wasn't finding another o ring and then I was thinking that it must have completely dissolved in the motor so I was thinking I must have more troubles than what I thought!
 
Once you have done a couple dozen water pump services on the (portable) Mercs (the 6/8/9.9 and 15 horse are identical), you can just about do them in your sleep in under 15 minutes.

They really are a simple and straight forward job with a minimal amount of things to replace.

Merc has three different "waterpump" kits for these.

One is simply the impeller, one also includes the seals (except that one in the cover that always needs replacing) and then they have the "total" kit which even includes a new base etc (but still doesn't include the cover seal - go figure).

I usually opt for the middle kit (impeller and seals) plus spend the extra couple bucks for the cover seal.

If you watch Ebay in the fall/winter you can usually pick them up from a couple of the Merc (stores) for less than half price.

I recommend changing the impeller every second year and the seals with every second impeller change (so 4 years between seal changes).

Just about the only way to kill these motors is overheat them, so keeping the waterpump serviced is the cheapest way to keep them running well.

I have 86 and 87 model year 9.9's and a 1991 15 horse.

Aside from waterpump, gear oil service and new sparkplugs (I do the plugs every year - buy them in bulk for less than 2 bucks a piece) they have never needed anything else.

Take care of it and it will probably outlast you...
 
Could be any number of reasons including:

Impeller is getting shot
Seal on the waterpump (cover or base) is shot
Hole in the water tube
Blockage in the water pick-up (that feeds the waterpump)
Crud that got sucked in blocking the waterpump or lodged in the water tube
Blockage in the powerhead itself (the water jackets a big, the channels are tight)

Maybe a few other things that don't immediately come to mind.

When was the waterpump last serviced - if the answer is anything longer than "last year or this year" it is well due...
 
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