so i recently swapped a low mileage motor into my f4i stuntbike and im running into a problem that i cant figure out...when i start the bike up, let it warm up to 110-120, take it down the road a minute or so to my gas station (temp will get to 160-170ish) and turn the bike off, it will drip/leak coolant at a steady rate for about 20-30 seconds...the leak is definitly coming from the backside of the waterpump area...99% sure its coming from where the waterpump itself presses into the motor(looked underneath when it was leaking and did NOT see it coming out of weep hole). As soon as i fill up with gas, and leave from the station and let the bike warm fully up to operating temp, the leak stops and doesnt start again unless i let the bike fully cool off again.

i figured the seals inside the pump were shot since the motor i just swapped in was sitting for 2-3 years, so i swapped in the waterpump from my old motor (didnt have this problem with last motor, oring looked fine)....swap in other pump, no leak at all for first day or two, thought i fixed it..third day of riding on new pump and its back to doing the same exact thing...leaks enough to make a good puddle under bike and smell up everything from dripping onto header but leak stops after riding it, maybe itll show one or two tiny drops on the bottom of motor but nothing like what it does. other than that rare possibility of the second water pump ALSO being bad, can ANYONE give me any other possible ideas as to WTF could be causing this??

what would allow the bike to leak while it warms up, but stop dripping once its warm? could a bad radiator cap be the culprit? that or another pump is all i can really think of. let me know what you think

thanks

 

you know, the with the front tire to your left, the bottom right bolt in the water pump, is the drain bolt.
are you running water/antifreeze or just water? water gets hotter so it may effect it. other than the drain bolt i cant think of anything.

 

was the thermostat gasket! totally didnt think of that because i thought i saw the coolant coming out of the pump but it was really just draining down from way up top and making a mess everywhere...did a record time thermostat swap from my old motor and (knock on wood!!) no more leaks!!