Milky Discharge from vent tube

Today i went to the track and warmed up my bike. i have a 03 yz450 I rode a few laps and came back and as i was putting my bike on my stand i noticed a milky substance on my stand. I called my friend over to look at it and he said it wasnt a good sign. i am new to fourstrokes and i wasnt sure what the problem was. He told me it was one a few issues a blown headgasket seal or a cracked head. i checked my fluid in the radiator and it hasnt dropped since the last time i filled it which was about a week ago when we changed the water impeller seal. so my question is, how can i narrow the problem scenarios down. the bike runs strong and doesnt over heat, it doesnt smell like its burning coolant in the oil, its never done this before, and it got below freezing here which it hasnt done in over a year since its warm az. at first i was super bummed and pissed thinking it was somehting serious. i checked my dipstick abd the oil looked fine to me. if the coolant and oil had mixed completely what color with the oil be? im gonna change it first thing in the morning and i wanna know what to look for to determine my problem. im thinking it was condensation from the cold weather and it being run for the first in a week or so. LEt me know what you guys think thanks a lot.

If you are talking about the crank case vent tube it is perfectly normal. We have owned 6 Yamaha's since 06 and every one of them does that. Its just a bit of oil coming from the vent. We tend to notice it more during arenacross as the bike tends to get a bit hotter but its nothing to worry about.

I use to have a WR400F and now i have a 00´YZ426F, and some times they do me the same, its a brown mixture that (from the smell) i think its some gas mixed with oil, that leaks from the head breather, and the oil and water still ok... I don´t know how to explaine it but it hapens sometimes when you kill the engine...

Don´t worry...:moon:

I had it on my 05 and 06. Now, if you change the oil and it's that color, thats a different story.

It's usually moisture condensation from the air collected in the vent tube, and nothing to worry about as long as the oil itself looks good. If the actual oil in the tank or crankcase takes on that texture and appearance, that's bad.

Thanks guys im gonna go change the oil in a little bit and see what it looks like.

Did you change your oil? I hope it was okay.

no i didn't got called into work so my next day off is wednesday i'll let you know then. i did check the dipstick that day and the oil was good color and after another ride the vent tube leaked a tiny bit of black oil so im sure it was just condensation since we had a huge temp swing here. i'll be sure to let you guys know!

Hi all,


Apologies for reviving an old thread but I thought it better than to start a new one for an issue that's been covered plenty times before.


I just joined the forum today to seek advice. Following a short ride out tonight, I noticed a "milky oil" puddle on the ground directly underneath the head breather hose (it's never done it before). I checked my dipstick and the oil looks fine, I will do an oil change tomorrow to make sure but thankfully it's looking like condensation rather than something sinister.


The only question that remains unanswered for me is the amount of "milky oil". The puddle under the bike was about 2-2.5" in diameter, which seems like an awful lot? Could this amount still be put down to condensation?


Thanks in advance for any replies!

If you think a 2" puddle is a lot of oil, put a teaspoon worth on the floor and come back to look at it in 3 hours.

If you think a 2" puddle is a lot of oil, put a teaspoon worth on the floor and come back to look at it in 3 hours.

A good way to look at it.

Changed the oil and had no water/milk in it, great news.

Oil had a bit of a green tinge though, and had a whiff of petrol to it, not something I've seen before.

ImageUploadedByThumper Talk1399496310.453354.jpg

The green "tinge" is normal for many oils.

Coolant in oil either totally separates or blends into a milky foam.


Very significant amounts of fuel can be introduced into the oil simply by cold starting the engine once without letting itwarm up completely and running it for at least 10-15 minutes.

Thanks for the replies!

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