6 replies to this topic
  • YamahaYz450F

Posted August 10, 2004 - 05:35 AM


I have a 99yz400f and when I started the bike this weekend I let it idle for about 5min but then as i noticed that coolant was just pooring out of the overflow. if you know howw to fix this problem please let me knoe

thanks matt

  • ncmountainman

Posted August 10, 2004 - 05:38 AM


don't let it idle so long! :thumbsup:

  • YamahaYz450F

Posted August 10, 2004 - 05:46 AM


Well also when i started it at the starting line for and let it idle for about 2 min it was pooring out as well

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  • ncmountainman

Posted August 10, 2004 - 05:53 AM


maybe your waterpump is goin out i put a boyeson on mine and love it way more stable temps. sometimes your timing (valve or ignition)wilk make it hot or could be lean jetting also.hows it run otherwise? :thumbsup:


Posted August 10, 2004 - 10:07 AM


I doubt the water pump is failing. This was and remains an issue with the 99YZ's and WR's. The stock cap does have a weak spring and tends to give up coolant quicker as they age. Take your cap to your local autozone or advance auto and pick up a replacement cap for $6.00. I have replaced the cap on my 99 YZ twice since it was new this way. The other thing that I did was install a WR overflow bottle on both my YZ's so that when it does overheat from time to time in 90 deg plus weather in the tight woods with no air movement, that my precious and expensive engine ice is sucked back into the radiators as soon as I can open her up and cool her off again......

Bonzai :thumbsup:

  • oldNslo

Posted August 10, 2004 - 11:19 AM


I have an 00 YZ426F and have the same thing happen to me. If you do a search on overheating and related subjects here on TT you probably find many many comments on this issue. If I let her idle much longer than 2 minutes the header gets glowing red-hot and not much longer after that I'll get a little coolant overflow. It's really not a problem, just don't let the bike idle for extended periods as well as checking your cap and coolant level. :thumbsup:

  • YamahaYz450F

Posted August 10, 2004 - 06:03 PM


Thanks for the info. the header dosen't get to the point where it is red hot. but the coolant just leaks out. ill try the new radiatior cap and if the dosent help ill try some more stuff.. but thanks for the info

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