yz400f coolant leaking....but no hoses leak

3 replies to this topic
  • tattoo79

Posted April 01, 2011 - 12:18 PM


so i just got this bike on a trade....great bike...idles fine...runs great
i just took it out for a quick ride and when i came back and parked it
ive got coolant dripping down on the right side...well its not the radiator or the hoses...it looks like a tiny hole at the bottom of the motor, seems to be coming from there?? is that normal:ride:

  • grayracer513

Posted April 01, 2011 - 12:56 PM


It's normal when the water pump seals go bad, yes. The hole is there to keep coolant from getting to your engine oil.

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  • tattoo79

Posted April 01, 2011 - 12:59 PM


:banghead:ok thanks for the reply.....is this aa hard fix??

  • grayracer513

Posted April 01, 2011 - 01:11 PM


Uh uh, no, not really. :cheers:

Probably more work than you'd like it to be, but not bad. You will need to drain the oil as well as the coolant, and remover the right side crankcase cover. This will allow you to hold the impeller shaft with a wrench in the flats ground in it for that purpose, and to change the oil seal as well. It also makes it possible to inspect the shaft for a groove worn into it by the seal. If you can feel the groove distinctly with your fingernail, it needs replacement.

The biggest mistake most people make with this job is putting the seals in backward because they look normal when you do that. The lips of the seals need to face toward the fluid they work against, not toward each other.

The other mistake is to let someone talk them into shortcutting the job by trying to unscrew the impeller without removing the case cover from the engine. The risk in that is in breaking the drive tab off of the impeller shaft, possibly damaging the engine balancer, and ending up having to take the cover off anyway.

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