Wr250x is leaking oil from breather lube

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I was riding on the freeway and it was leaking oil all over on the rear wheel. Took it to the shop, found out more oil in the airbox, mechanic did the leak down test and result came out to be 2-4%. He said it’s accpetbale and no clue what’s the cause of this leak?

2008 Wr250x with 5k original miles with a 290cc big bore kit(came with the bike when I bought it) Please help, thanks a lot!
 
byke

byke

Well-known member
Oil out the breathers is a classic overfill symptom. Did you just change the oil?
 
mototireguy

mototireguy

Moto Tire Veteran
byke said:
Oil out the breathers is a classic overfill symptom. Did you just change the oil?
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+1

Typically the result of oil overfill.

It's normal for a little oil to vent into the airbox. Lots of high rpm freeway time maybe a little more oil but not lots.
 
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Thank you guys! I didn’t not drop it or tip it over.

Bought the bike at 5000 miles, took it home and did an oil change, drained all the oil(surprisingly, there was not much oil inside?! Like 0.25 quart of old oil) so I added 1.4-1.5 quart of oil with a new filter. It was running fine. At 5200 miles, I was riding from San Francisco to Alice’s, it was leaking oil when I got to Alice’s, so I didn’t continue at Alice’s, rode it to San Mateo, more oil leak.

My buddy drove me home to get my truck, loaded the bike up on my truck, dropped it off at a local SF shop, I noticed there was a lot of oil on my truck bed(the bike was completely off)
 
M

motomania2007

TC/MSF/CMSP/ Instructor
Too much oil starts to accumulate in the air box and does so usually as a result of sustained high engine speeds. For example, it does it less in round the town riding and does it more at sustained freeway and highway speeds.
 
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motomania2007 said:
Too much oil starts to accumulate in the air box and does so usually as a result of sustained high engine speeds. For example, it does it less in round the town riding and does it more at sustained freeway and highway speeds.
Click to expand...

This is my 5th Wr250x and I never had any problems like that when I was riding on the freeway a lot with my previous stock wr250x. Do you think the 290cc big bore kit is related to this issue?
 
M

motomania2007

TC/MSF/CMSP/ Instructor
Big bore kit = more air movement inside the crankcase and therefore more sensitive to oil level.

Too much oil causes the crankshaft to splash in the oil and pretty quickly a thick mist of oil inside the crankcase and the mist is thicker than the engine was designed for. Mom x that with a big bore that moves more air than the crankcase was designed for.

If the rings we're not sealing well then you get more blowby that forces the oil mist out the crankcase breather...
 
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Thank you for all the help guys, another shop recommenced a top end rebuild, what do you guys think?
 
2strokeYardSale

2strokeYardSale

Moab on my mind
Remove whatever oil is in the airbox now. It's just going to keep leaking.

With a clean airbox you'll know if the crankcase breather is blowing oil into it after a properly filled oil change.
 
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2strokeYardSale said:
Remove whatever oil is in the airbox now. It's just going to keep leaking.

With a clean airbox you'll know if the crankcase breather is blowing oil into it after a properly filled oil change.
Click to expand...

I disconnected the other end of the breather tube and connected it with a small bottle oil catcher there. Cleaned everything and took it for like 30 minutes ride. I noticed it was leaking a little bit oil in the small bottle. I will try to do an oil change and see how it goes, thanks!
 
kxmike

kxmike

Well-known member
My DRZ and other bikes come with an oil separator that traps the oil in the mist and drains it back to the crankcase. The gases are routed to the airbox. Perhaps the previuos owner got rid of the separator and just routed the hose directly to the airbox? (not sure if the Yamaha comes with a separator but it would eliminate your problem).
 
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