strange coolant leak

[oldguy]

This morning we drove 200 miles to a race in temps around 29 deg F and once there my son started up his YZ450F to warm it up before practice. As it was sitting on the stand idling I noticed a steady drip from under the waterpump housing. He shut the bike off and we checked the bolts- all were tight- and the hose connections (again all tight). I had him start it up again and told him to run it up to a friends trailer since I just had the bare necesities for tools along today. When he got to the other trailer the bike had now warmed up and there was no leak. I checked the coolant level which was good and he headed out for practice. Once back I again checked and found no sign of a leak and the level was good- I checked after each of 4 motos and again no leaks or drop in level.
At first I was worried about a seal leak or shaft problem but now I am wonderring if the 3 hours in the back of a pickup truck at those temps could have made the o-ring (I think that is what is in the waterpump cover) shrink allowing a leak until the coolant warmed up and the o-ring swelled up again?

Any other ideas?

 

[wornknobby]

Did you double check to make sure it wasn't running out the overflow tube and onto the frame? I've seen this happen before and drove the owner nuts. :laugh:

 

[oldguy]

Yes I checked that first but the overflow is on the other side of the frame. At first I thought I had spilled some coolant when I checked the level before loading up but when we saw the drip I looked under the bike and could see it was coming from the waterpump cover.

 

[wornknobby]

well what i would do is let the bike lean on the waterpump side over night and see if there is even any residew on it the next morning. The i would just run it and see if she leaks any more. If not then maybe it was justa freak occurrance.?? I'm really not sure.

 

[phranticness]

if you have a cooling system pressure tester I would recomend pressurizing the cooling system. Your cap is probablly a 1.1, (roughly 16psi I belive). if thats not availible remove the coolent pump cover and inspect the seal. I'm sure the seal is a pretty cheap part and even cheaper insurance to just replace it............happy trails.

 

[oldguy]

if you have a cooling system pressure tester I would recomend pressurizing the cooling system. Your cap is probablly a 1.1, (roughly 16psi I belive). if thats not availible remove the coolent pump cover and inspect the seal. I'm sure the seal is a pretty cheap part and even cheaper insurance to just replace it............happy trails.

that might be but not related to this problem- leak was no where near the cap of overflow tube and it actually went away under the highest pressure

 

[phranticness]

I just was refering to the cap relief pressure for the appropriate pressure to test at. Pressurizing the cooling system when the bike is cold should simulate the conditions when your bike was leaking..........Although I have to admit thats a weird one. Please keep this thread updated when you fix it...........good luck.

 

[biglou]

My guess: Thermal contraction of the metals in the pump housing and case.

 

[oldguy]

I just was refering to the cap relief pressure for the appropriate pressure to test at. Pressurizing the cooling system when the bike is cold should simulate the conditions when your bike was leaking..........Although I have to admit thats a weird one. Please keep this thread updated when you fix it...........good luck.

Sorry I read to much into your first reply :whoa: I'll try this weekend to do a pressure test hopefully it will stay cold enough to replicate the problem (without driving 200 miles in circles :whoa: )

 

[76GMC1500]

At first I was worried about a seal leak or shaft problem but now I am wonderring if the 3 hours in the back of a pickup truck at those temps could have made the o-ring (I think that is what is in the waterpump cover) shrink allowing a leak until the coolant warmed up and the o-ring swelled up again?

That's what happened to the space shuttle. Some o-ring materials lose their resilience at low temperatures. That o-ring is most likely made of neoprene, but I haven't heard of any low temp issues with neoprene. The operating temperature range is -45 to 230 degrees F.