'85 7.5hp, rebuilt water pump. Still issues with water flow to engine

ianmoore

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Jun 5, 2014
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Hello all,

End of last summer was out fishing, using kicker and it started smoking and stalled. Didn't see it, but was not peeing correctly.

Started messing with it this spring. Motor works fine. Good compression. Figured there was probably salt buildup in water lines. Flushed out all channels(flushmount, direct inset to engine, pickup tube) they are all clear.

I rebuilt waterpump and reinstalled following manual, including all torque specs. impeller is well seated in key and spins with driveshaft as it should. Splines are all pointing clockwise. Put the motor in a barrel and its still not getting enough water to the engine. I dropped the LU again to check, top water cover top off and it all looks fine.

I actually am using the waterpump base that came with engine when I bought it(couldn't find an oil seal that fit the base i bought), but the base is in good shape. Didn't see anything that would make me worried about it. New Insert, new top new plate, etc. new seals on water pick up and

The only other thing I can see is that the flush port is leaking.. This is a conundrum, because the part that Mercury lists, Mercury 10-79953Q04 (a common drain fill screw) is too small for my flushport. I also don't think this could be the whole issue because before I put in current bolt, the old one was completely sealing the opening. I removed it after the motor started having issues because it was becoming too difficult to take out.
 

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racerone

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Some will argue.-----Since motor overheated and stalled you should post the actual compression values.----Or remove bypass cover ( 3 screws ) and look at pistons and rings.-----On severe overheat the plastic washer at the top of the water tube melts and often blocks water flow to the power heed.----The factory replacement is improved.
 

ianmoore

Petty Officer 2nd Class
Joined
Jun 5, 2014
Messages
178
Some will argue.-----Since motor overheated and stalled you should post the actual compression values.----Or remove bypass cover ( 3 screws ) and look at pistons and rings.-----On severe overheat the plastic washer at the top of the water tube melts and often blocks water flow to the power heed.----The factory replacement is improved.
I did check compression. I don't remember exactly what it was, but right around 120 on both cylinders.

I've never had an outboard overheat, so I don't know how severe it was, but if the plastic washer had melted, wouldn't that prevent the water from running through the system? If tried flushing using both using the flush valve(on the side) and connecting to where the hose exits the engine(flushing water that way). Both seem to have a nice flow, which makes me feel like there is nothing impeding the water from there.

What factory replacement are you talking about?
 

racerone

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Water must be 6" above the impeller in your bucket.----And good luck with the motor.
 

ianmoore

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Jun 5, 2014
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178
Water must be 6" above the impeller in your bucket.----And good luck with the motor.
It is. Thanks. short of repeating the steps over again, I'm a bit at a loss.
The only thing i can think of is to connect a hose to where the water guide tube connect to the tube that goes to the engine. I don't know the exact schematic of the coolant system with the motor. Maybe somehow through the flush and the top intake I'm able to get good flow to the bottom, but somehow not from bottom to top..
 

ianmoore

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Jun 5, 2014
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I wanted to send an update if someone is in s similar situation.
There is a great troubleshooting video on how to check through issues with lower unit. In my case, pump in new waterpump and impeller, spun it on drive shaft, and then installed, but wasn't getting much water up through the engine and it was overheating.
I was able to take lower unit out and try spinning drive shaft with drill as in video. There was water coming out of the pump, but nowhere near what he was getting. I have ordered an OEM water pump and I'm going to try again.

As I noted in the first post, the impeller seems to be spinning slightly askew. Short of a defect in part of the pump, I have no idea what could be causing it. The pump sits solidly on the metal ring around the bearings.Anyway, at least I know my water pump was underperfroming and hopefully can get enough water pressure with the new pump

 

racerone

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Pump impellers are offset in the housing.----Have to be in order to work.
 

ianmoore

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Pump impellers are offset in the housing.----Have to be in order to work.
Just to make sure I'm clear, the impeller isn't sitting it the middle of the waterpump. As it spins, one side is closer to the side walls. Is this what you are saying? I guess my assumption was that the impeller would have the fins equidistant against the walls of the water pump
 

racerone

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None off them sit in the middle.-----It will not work if it was as per your thinking !
 

ianmoore

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None off them sit in the middle.-----It will not work if it was as per your thinking !
I was hoping that was the issue. I'm not getting enough water through the top spinning the drive shaft as in the video.
I'm gonna rebuild waterpump again. Ordered an OEM part so should be able to use the base as well.

I just can't figure out why the water pump isn't pumping enough water. the base was in the motor when it was working and when I inspected it, it looked to be fine. Everything else is new, and there is no clogging in the pickup tube.
 

ianmoore

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by your definition it seems that the impeller/pump system is a bit weak.
I was getting water, but nowhere near what he was getting. I'm including my video for reference. Looked like about 4-5" max.
I also tried blowing air into the water tube and did get air coming out of engine block waterline, but it was pretty faint. When I tried blowing air into the engine water line, I got a loud wooshing sound through the midsection, and little pressure coming out of bottom line(that would attach to water pump.) I assumed the water line would have somewhat of a vacuum to maximize flow to engine,only coming out the engine block or flush hole(if it were open)
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ianmoore

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Jun 5, 2014
Messages
178
I also seem to have an oil leak coming from the shift shaft. I don't want to throw any more money at this until I figure out the coolant issue(hopefully solved with new waterpump).
I know I won't know for sure until i take this apart, but do the bushings tend to hold up? Would a leak typically be solved with a new seal and o-ring? Those bushings are expensive!
 

ianmoore

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Jun 5, 2014
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I am currently traveling for work, but plan to install the new waterpump when I'm back. Im getting concerned that, though the waterpump i installed might not be perfect, it is working, and that makes me think that the issue would be somewhere else.

To this point I have
-rebuilt water pump and replaced impeller
-run weed eater string up through the channels to see if I could loosen anything
-run pressurized water into water uptake tube, and the water exit from power head
-run pressurized air into all the water inlets.

The one thing of note was that when I ran air into the engine water inlet it seemed that the air wasn't just going down through the water uptake tube but through the whole middle cavity. I couldn't visually see anything, but am not knowledgable enough about these motors to know if this is an issue or not.

Assuming my rebuilt water pump doesn't solve issue, what would you do as a next step?
-Remove port head and see if there is any blockage there?
 
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