1977 Mercury model 45 (4.5hp) water pump

[dgfinck]

I just replaced the impeller in my 1977 Mercury 45 (4.5hp). The old one was completely torn up. I cleaned out all the impeller pieces, cleaned up all of the water pump and inlet tube parts, replaced the impeller, reassembled the water pump, and carefully aligned the tube guide on the pump with the tube going up to the power head as I re-installed the lower unit. I placed the LU in a bucket full of water (muffs don't work; the water intake is above the prop, not on the sides of the LU) and started it up. After a second or two, water came out of the tell-tale beautifully, and continued to do so for about 15-20 seconds, at which time it stopped. I tried increasing and decreasing the RPMs with the throttle, but still no water from the telltale--so I cut it. I was worried the new impeller was ruined already. I re-removed the LU, opened up the water pump, and the impeller is fine. So I re-re-assembled, re-re-installed the LU and tried again. Again, water came from the tell-tale for about 15-20 secs, then stopped. So I cut it off, again. I blew compressed air in the tell-tale hole, and air comes out of the lower-unit water inlet and bubbles up in the bucket--so there doesn't appear to be an obstruction. I tried once more--same result--telltale water for 15-20 secs then nothing.I have a Clymer manual, and it doesn't mention anything about the existance of a thermostat on my motor.What could be causing the water to flow for 15-20 secs then stop?????Thanks,Darren Finck

[sledhead041]

Did you make sure u had ALL of the impeller cleaned out? Sounds like you have a piece still in the cooling system. You can try to remove the hose for the tell-tale and then start it to try to flush it out. Good luck buddy!!

[dgfinck]

Well...1) I took the lower unit off, put it in a bucket of water, and spun the drive shaft with a drill; water pumped out of the plastic tube on top of the water pump. So the water pump seems to "work" (I don't know how much pressure it generates, though).2) I hooked a water hose up to the tube in the drive-shaft housing ("leg") that the water pump feeds, and water streams constantly out of the tell-tale. So the powerhad cooling "works" (I haven't tried running the motor while cooling it with the water hose fed up the tube yet, though)...I can't think of a good reason why water would stop coming out of the tell-take after 20secs of running... any other ideas?Thanks,Darren