Help on diagnosing milky oil

Okay, let me first say that I've searched the forums and found out that:

Milky oil WITH low coolant levels mean (obviously) that the coolant is somehow getting into the oil. *this is me*

Unless the water pump weep hole is completely blocked, it's impossible for the source of coolant to be here without both seals being blown and seeing coolant/oil out the weep hole.

Main suspects are the head gasket and the o-rings between the cylinder and case. *most probable so far, with my knowledge*

SO, here's my condition....just picked up an '05 450 from a guy (at a very attractive price after finding these issues) and the oil is waaaay too full after running for 5 or so minutes and is a milky color (more greyish than white) and the coolant was low. The motor sounded fine, started well, and ran smooth with a slight power loss compared to my other one.

What I am wondering is there any other component that could cause the coolant --> oil mix other than the head gasket and o-rings? While I have it apart, I plan on a new topend (I don't know how many hours are on it), including piston/rings/timing chain. Any other ideas, I'd like to have all the parts available when I tear into it.

Thanks a bunch!!!

its either the top end, or the water pump...that is the only 2 places where the water can come from. i has a similar problem on my YZ250, it was the water pump in my case, just poped 2 new seals in it (make sure u use some white lithiam grease on the inner races of hte oil seals. but i also had experience on a firends 1989 KX250, it leaked both at the head gasket and the water pump. both faily easy fixes, the worst part is waiting for hte gasket kit in teh mail.

You really did search, didn't you? :ride:

So, I'm going over old ground when I point out that your most likely points of entry are, the head gasket, and the the O-rings at the cylinder base and right engine cover. It's possible for any component that carries water and is exposed to oil on an adjacent surface to have a crack or porosity leading from one passage to the other, too, so that could include the crankcase itself, the cover, the cylinder, and the head. That kind of thing is pretty rare, though.

There is a plug near dead center in the head that has a hex socket in it. That leads to the water jacket, and could be leaking.

Out of everything, the head gasket is by far the most likely.

Thanks Gray!!! Yeah, I was hoping it was something simple like a gasket or o-ring. I think I'll order all of those parts, replace them all (including the water pump seals and shaft) and most likely fix the problem. I have done the water pump area before on another YZ, and it's not that bad of a deal. While I'm in the head, is there anything besides piston/rings/timing chain that should be done?

Thanks again!

Check the valve clearance before you tear it down, it's a perfect opportunity to make corrections. If you feel ambitious, you can solvent test the valves. Valve springs are very cheap on YZF's and since you have the opportunity, you can replace them and not have to worry about them breaking (they don't usually). New valve seals are a good idea, and as long as they're loose, you can have a look at the valves themselves.

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