250F Help with my yz250f

I’m not very experienced working on dirtbikes but my 2016 yz250f has been getting foamy oil. I suspect that the coolant and oil are mixing due to a head gasket but it’s not burning coolant. It doesn’t smoke when I start it up. I’m confused. Please help.
 

SRAD97750

Moderator
Staff member
Yes, foamy oil is a sign of water in the system. Usually a head gasket is the point where the two mix.
Does the coolant look like milkshake as well?
Does the coolant bubble wildly if you remove the rad cap after you first start it up cold?
Does it push coolant consistently out the overflow hose even when the bike isn't hot?

I imagine you know what you have to do, but these questions may help you prove it's the head gasket.
-BIG DAN :thumb:
 

SRAD97750

Moderator
Staff member
The yz250f water pump utilizes 2 seals, one for oil and one for water, both separated by a chamber that has a weep hole open to the atmosphere.
It would require both seals to fail, and allow fluids to pass over the weep hole chamber for them to mix at the water pump.
I guess anything could happen though... :noidea:

YZ250F double seal with weep hole cavity
YZ250F.jpg


KX500 Single Seal (fluids on each side of one seal)
KX500.jpg

-BIG DAN:thumb:
 
The yz250f water pump utilizes 2 seals, one for oil and one for water, both separated by a chamber that has a weep hole open to the atmosphere.
It would require both seals to fail, and allow fluids to pass over the weep hole chamber for them to mix at the water pump.
I guess anything could happen though... :noidea:

YZ250F double seal with weep hole cavity
View attachment 33408


KX500 Single Seal (fluids on each side of one seal)
View attachment 33407

-BIG DAN:thumb:
Didn't remember that when I just built the 14/15 I have (2 years ago). Yamaha 4 stroke is like the 2 strokes. So the gasket could be leaking like the 125 2 strokes are prone to where the water transfers between inner and outer right case.
 
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