Not Quite Water Proof

Living in Northern Alberta means that I do alot of riding off road with friend who have quads and side-by-sides. The trails often are full of mud holes and not exactly the type of terrain an MX bike (07 yz450f) was designed for. After my last ride I had to change the oil because it was milky and grey. I was afraid that water had gotten into the case some how. I don't think it could be a seal problem b/c th bike is brand new. At points the bike was almost completely under muddy water but never stalled. I am wondering how this water could have gotten in. I have two thearies myself. First I'm thinking that when the hot bike was suddenly cooled by hitting the water the vent lines may have sucked the water up as the fluids contracted. Second, i have noticed that where the wiring enters the case near the oil fill plug the rubber gromet maybe not be making a perfect seal.

When I ran these thought past a machanic at the local shop he suggested putting check valves on all the overflow lines. If I could get some feedback from the offroad guys on keeping the water out that would be great.

If the water was as high as the bottom of the frame, and you stalled and/or started it, or ran at speeds near idle, the crankcase vent likely drew water into the engine. It won't ordinarily do this at speeds above an idle, because the air pressure in the crankcase rises and falls too quickly in response to the piston moving up and down for water to be drawn fully up the tube before the pressure reverses again. At very low, or cranking speeds, or just as the engine stops, it is actually possible, though. If you do this kind of thing a lot, you should consider the following:

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