70hp Yamaha weak water flow at idle

[Wayne Burgess]

My 1987 70hp will sound the alarm (steady buzz) when running at very low rpm in forward and the water stream seems to be weak. I have had the water pump replaced twice, both times the impeller was split on the inside. The next time out the water stream was still weak and the alarm continues to sound when barely above idle in forward or idling after a few minutes. Any suggestions? The motor runs great except for this.

 

[kmarine]

Re: 70hp Yamaha weak water flow at idle

When you replaced the impeller did you check to see if there were any burrs on the housing which could be tearing it up. Something like this even corrosion could instantly damage the impeller. You could also have a piece of old rubber lodged in the cooling passages. when the alarm goes off did you test with an infared thermometer to get engine temps or find hot spots? Try these first in your search. how often are you replacing the impeller?

 

[99yam40]

Re: 70hp Yamaha weak water flow at idle

check to see if that motor has a PRV that is sticking open and dumping too much water at low RPM

So far as the splitting the impeller, are you replacing with a kit or just the impeller?
using a little lube when installing impeller and making sure you do not start motor without water to the pump is a very good idea

 

[Wayne Burgess]

Re: 70hp Yamaha weak water flow at idle

Both previous impellers were installed at different shops by marine technicians, I asked the Tech that installed the second impeller if he could do a rebuild kit as the problem was reoccurring, he said only the impeller was available. I have not checked with an infrared but I have pulled the cover and the motor did not feel that hot to the touch.

 

[99yam40]

Re: 70hp Yamaha weak water flow at idle

need to look up and by kit on line if your local Yamaha shop does not have them