2015 YZ450f Coolant Leaking out of Valve Cover Vent Tube

There is coolant coming out of what I am assuming is a oil vent tube on the right side of the motorcycle that comes off of the head.  Here is the interesting part though, it is not mixed with any oil, and upon draining my oil it was NOT milky.  We performed a cooling system pressure test and it held 25 psi no problem.  It would lose pressure as the bike was kicked over though. Could this be a strange head gasket problem? Or does anyone have any ideas? Thanks in advance

Looking at the parts diagram for your bike seems to me like a valve cover gasket is probably bad.

Edited by blurinthewoods

Uh, no.  The valve cover gasket has nothing to do with coolant.


Since your oil is not milky, I will assume this is yet another case of condensation in the crankcase vent tube, a very common occurrence in more humid environments.  Atmospheric water condenses inside the tube, then mixes with the oil residue it finds there and drips out looking like the dreaded "milk shake" kind of goop.  Nothing to worry about.

Yes but if you read correctly I did not say valve cover gasket. And my radiator drains in about 60 seconds... So this is definitely a concern for obvious reasons

Is the bike smoking? Any pics of this drain tube? I don't know of any plausible way coolant would come from the valve cover bleeder without already being in the oil...

Yes but if you read correctly I did not say valve cover gasket. And my radiator drains in about 60 seconds... So this is definitely a concern for obvious reasons


If you read the first response to your post, "blurinthewoods" did.  Where is the coolant going?  Does the oil level rise as the coolant disappears?

I'm guessing the tube you are talking about is the radiator overflow hose.  Small pinkish colored hose?

Sorry Grayracer I missread, but the coolant is coming out of the black hose that comes off of the valve cover, not mixed with any oil, no change of oil level. I kid you not, it is straight coolant no oil.

but I am NOT talking about the radiator hose cowboyona426, Its a thicker black hose that is literally connected to the valve cover.


And billygildark, I would have said the same thing myself, but no smoking, It really makes no sense but somehow it is happening.

So if you remove the valve cover can you see coolant anywhere? It's gotta go somewhere as grayracer implied..... Either on the ground, in the oil, or out the back end...

I knew what hose you meant right away.  Wonder how.


Is this "coolant" significantly green, or is it just water?


If you slowly remove the drain plug from the crankcase, does water/coolant come out first, or just oil?

So you have removed the valve cover and inspected everything right.

Sorry if a bad idea but a pondering idea....

Do you live in a very cold temp winter and store the bike in freezing conditions without draining coolant/water?

Maybe a coolant jacket in head is cracked just in the right spot allowing coolant to pass threw when the motors running?

I'd imaging it'd still smoke horribly though...

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