Yamaha 90hp 4 stroke water flow problem and overheat 2011 F90 TLR

[BrianComer]

Got this boat on Friday. 5 minutes after putting in water the overheat alarm sounded. Shut motor off. No water coming from pee hole so removed lower end and replaced water pump-entire kit. The impeller had nothing left for vanes. Removed all the broken impeller pieces from pump. Also found a lot of impeller pieces behind the water intake screens on skeg. Cleaned all out. Reassembled pump and re-installed lower end.
No water from pee hole unless running at 1500+ RPM. Motor still sounds overheat alarm.

Checked thermostat--all good. Removed and inspected pressure control valve. Looked okay-just a spring and plastic valve.

Ran motor with water house connected to flush port. Plenty of water through pee hole and motor does NOT overheat or sound alarm if water is forced through using the flush connection.

Remove flush connection and back to original problem.

This motor has 95 hours on it. What else needs to be checked or could prevent water from properly circulating through the motor? Is there a diagnostic flow chart to troubleshoot such problems?

[99yam40]

There is a good chance the pump housing is bad or pieces of impeller are plugging up some passages

[fairdeal]

seems like a good chance that one or more pieces of the impeller are occluding a water passage.

I would drop the LU, remove the thermostat,
jerry rig a way to connect the garden hose to the thermo housing
and try to backflush the heck out of it.

I don't think you're going to find a troubleshooting chart that applies

Yamaha expects the impeller to be replaced before it totally self destructs

[BrianComer]

Upate

Here is update.

I decided to change the water pump housing just to be sure and noticed that the impeller kit the dealer sold me originally did not seem quite right. Turns out the impeller was an 1/8 of an inch shorter than it should have been. Got another kit with right impeller and all is well. A lot of aggravation and a lot of time spent chasing a problem that did not exist except for a wrong replacement part.