Yz450f oil leak??! Need help!!

Jan 3, 2021
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8
3
2018 yz450f set up with a c3 thermostat, full PST engine jacket and full Skid plate. Has been running at a constant temp of 189°F. Oil is leaking through the black breather tube coming out on the right side coming down from the head. Had this problem since December 2020 took it to my Yamaha dealer and it sat there for 4 weeks and their tech said it was over heating and causing it to leak oil, he replaced a fitting and charged me $300 and sent me on my way. Nothing changed, still leaking oil. Not sure why and I just want to ride!!

Need some suggestions on what it may be.
Thanks.


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wwillf01

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Heber Ut
I would drain the oil and measure what comes out.. on the ktm we have I end up only being able to put 800cc of oil for it not to come out the breather. As long as your oil level stays in spec I would not worry. Is your temp coming from the radiator or the head.

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Jan 3, 2021
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I would drain the oil and measure what comes out.. on the ktm we have I end up only being able to put 800cc of oil for it not to come out the breather. As long as your oil level stays in spec I would not worry. Is your temp coming from the radiator or the head.

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I believe it is coming from the head. I did an oil chang when I first noticed it. Only about 250ml of oil came out. Oil window on the side ended up showing no oil. Yamaha oil change is only 600ml of oil. I’m not the first owner of this bike. Bought it back in November and had no problems for about 10 hours of ride time.


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wwillf01

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Right the breather is for the head... for my bike when I put too much oil... ie over half glass. Then I have to get the bike hot and riding it hard ... you can lengthen the hose and run it up high to try to gain a little more space for the oil to expand. That being said 250cc is scary if the bike was never upside down running and dumping oil.

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Jan 3, 2021
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Right the breather is for the head... for my bike when I put too much oil... ie over half glass. Then I have to get the bike hot and riding it hard ... you can lengthen the hose and run it up high to try to gain a little more space for the oil to expand. That being said 250cc is scary if the bike was never upside down running and dumping oil.

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My glass shows the add oil line at about 3/4 up. I guess I could do what you said and drain the oil and see how much comes out and just dump it back in, it’s fresh oil only about 40 minutes on it. I’m only 17 and this is my first bike so I’m learning lots. Thanks for the help man.


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wwillf01

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Sometimes when it is sitting with the kit it changes how it reads than with wheels so keep that in mind. I would pack oil and keep an eye on it ...if the bike is running fine then I would think you are fine.

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Jul 7, 2011
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I had oil coming out on my 15. From my experience oil was coming out from too much pressure in the head, due to a cracked piston, didnt take much from noticing to it not running though. Possibility of clogged oil passage cause extra pressure and oil leaving out breather
 

wwillf01

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This could be the case if it's running weird or the loss of oil does not stop going out of spec then you have some issue creating pressure.

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