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Discussion Starter · #1 ·
A few weeks ago, I reached out to you guys to help me identify a leak coming from the bottom of my CBR300R engine. Thank y’all for assisting me in getting acquainted with my water pump Weep Hole.

The leak was finally traced to that little hole, and was identified as coolant. The leak was not constant, meaning that it only occurred while at speed. Never a drop on the garage floor while the bike sat there. The leak was significant enough to get the inner bottom fairing dirty, but not significant enough to lower the level of coolant in any appreciable amount.

An intermittent issue, for me, is the most nagging issue. I ride in areas away from civilization with NO cellphone service. So, knowing the what and why helps me prevent those unplanned extended camping trips that leave you stranded in the middle of nowhere.

To those who introduced me to the Weep Hole, I want to introduce you to the... Open Pipe Mud Daubers

And so I set myself on a mission to perform a visual inspection of ALL of the components of my cooling system. And there it was, an Open Pipe Mud Dauber (a tiny insect that makes nests out of a cake of mud) had declared a homestead inside the breather hose of the coolant expansion tank that sits under the bike. By sealing this hose up, the dauber had turned an “open to the atmosphere” system into a closed one. And as the bike got to running temperature the expanded fluid was getting pushed through the seal and out of the weep hole.

Needless to say, I evicted the entire unborn family of daubers and added an open fuel line filter to prevent them from ever again making a home at the tip of my hose!
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