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Hi all, again,
I conducted a test last night on the water pump on my 77 merc 4.5. First I took the lower unit off the motor. I used my garden hose with a small nozzle on the end, and connected it to the metal tube, inside the mid section housing. Turn on water. A couple of seconds, and a nice stream from the pee hole. Then in reverse. Connect the nozzle to the pee hole tube, turn on water. Nice stream coming out of metal, inner tube. Now, knowing there's nothing blocking the system inside, i clamped the lower unit inside the water barrel, chucked up a drill to the driveshaft, and spun the thing. The amount of water coming out of the plastic water tube, from the pump, was approx. 1 -2 inches high. Like a water fountain. I'm no expert, but that doesn't seem like much.. How would this little bit of water go straight up, through the engine and be forced out the pee hole, like it's supposed to? Should I conclude now that the pump is shot? I'll hear what you guys say before I order a complete water pump. Thank again, RJ Lemay

iam no expert on it but it might seem you are forgetting pressure build up will force the water up into engine it has no where to go

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It seems to me since you get flow through the motor,you have determined that path is clear(although you my have used more pressure with a garden hose than a pump puts out)

I would double check all the sealing surfaces,plate,grommets etc

I had a defective design on a replacement water tube on a 10 HP Honda that after about 45 minutes running,the water forced the sealing grommet up the tube to where it wouldn't seal anymore.I had to braze a washer on the tube as a stop.

Anyway,my point is that if there is a way for the water to get past the seal on the tube,it won't reach the powerhead.

Make sure everything is fitting right down there( and check the seal where it goes into the powerhead....the garden hose just may have had enough pressure to over come some leakage up there)

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Can you pull the water pump apart? They are not magic devices, corrosion should be obvious, and clearances should be easy to check. What speed was your dirll running? Maybe it weren't fast enough. Was it running the right way? 2" is not a lot of height, but as stated above pressure will force it up. Did you put your finger over the pipe to see what sort of pressure there was? Were are not talking mains pressure here, but there should be some as it has to force the water up 3 feet through restriced pipes.

Take a piece of pipe, fill it with water, raise the end up the height of the motor and blow. You will see what sort of presssure it needs just to get it there. Once you have finished coughing and spluttering from breathing in water, tell us the results of the experiment...

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Your drill isn't hitting 1000rpm, about where that motor is going to idle, (1150 is fast-idle per Merc). There is no really sure way to measure cooling pump condition off the engine. Merc spec minimum is 3.0 psi at WOT measured with the gauge in place of the tell tale line.

Are you having cooling trouble, or just preemptively checking for a problem?

Normally you should replace an impeller every 3 years. The cost of the whole kit is cheap enough it really doesn't merit doing just an impeller-besides, just how many times do you want to take it apart? the whole kit is cheap insurance.

Trachappy is right, merc has,'t used an anti-grav cooling system yet. The pump has to do all the work.


IMNHO, if it's not broken don't keep fixing it until it gets broken.

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