coolant leaking out of water pump

I recently overheated my 99 yz400. For ahwile I could hear the water pump knocking rythmatically, but that went away after running more coolant through it. My problem now seems to be associated---coolant leaks out the bottom of the waterpump through an overflow hole? pressure hole? Now the bike will not retain coolant it leaks out that hole as soon as I run the bike a little. Is there a seal in there or something? The bike is not running hot anymore. Can I just plug that hole for ahile?

:thumbsup:

Sounds like you've got a leaking water pump seal. There are two seals on the impeller shaft. You'll need to pull the right side crank case cover off to get at it (The seals are on the the back side of the cover).

Smegol is right. There is one seal to keep engine oil in the engine, another to keep coolant in the water pump, and a gap leading to the relief hole you referred to so that the two fluids can't mix on either side. If you plug that hole, you'll defeat it's purpose, and encourage coolant to force its way past the oil seal. One of the last things you want is coolant in your engine oil. Trust me.

Be sure to check the condition of the shaft and the bearings, especially since you say you heard a noise from it.

And at that point it's probably a good idea to buy a new aftermarket impeller. :thumbsup:

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