40HP water pump problem?

[Roscoe P]

1st time boat owner looking for help. I just bought a used boat with 2000 Yamaha 40 HP 2 stroke (C40TLRY). The first thing I did was replace the impeller and test motor in tub of water, the stream was good. I took boat out next day for a few hours and had good stream entire time even at idle. When I got home and flushed the motor in the water tub it didn't produce any stream, not even a trickle. I pulled the lower unit and removed the upper pump cover and it appeared fine. Any help will be greatly appreciated.

[robert graham]

Remove and inspect/clean/replace thermostat and pressure control valve....but if your motor is running/cooling/peeing correctly during normal operation then it's most likely O.K....good luck!

[Roscoe P]

40 HP water pump problem?

Thanks for the quick reply Robert. I have a thermostat ordered but couldn't find the pressure control valve in the exploded diagram of parts for my motor. Can you tell me where it's located?

[boscoe99]

How deep was the tub? If the water pump is not submerged it will not pump water. The pump is several inches above the parting line between the lower unit and the mid-section.

[Roscoe P]

Thanks. The tub is deep enough for the water to be about ten inches above the lower unit seam while running.

[99yam40]

My thoughts are it is just your tell tail plugged up.
My C40TLRX has had it happen from time to time.
Scale/Crude breaks loose on the inside and blocks the passage
Blow some compressed air up it or just run a piece of weed wacker line up it while running

[Roscoe P]

I checked the tell tale and it's clear. The thermostat looked pretty crusty so I'm replacing it and just to be thorough (maybe too thorough) I've got a water pump repair kit on the way. Would someone tell me what to use in seating the metal bowl inside the plastic water pump cover when I replace it. Also Robert mentioned earlier in my thread to check the pressure valve but I can't locate one in the parts diagram for my motor and would like to know where it's located and how to check it. I work on stuff all the time, just new to boat motors.

[99yam40]

the small motors like yours do not have PRV

Just push it into place into housing by hand is what I do

Like I said if it does not come out the tell tail when you put it back together blow compressed air up it to move things around

[Roscoe P]

Thanks to everyone for your advice. I installed the water pump repair kit with housing and new thermostat. Motor has a strong tell tale now. I plan to take my family to the lake tomorrow and enjoy. I appreciate the help and have a great weekend!