Help...YZ450 with coolant in the oil

2 replies to this topic
  • dbreezy81

Posted October 29, 2010 - 06:08 AM


I am stumped. I recently purchased a 2008 YZ450 that the seller claimed had a completely rebuilt motor. I test rode it and power felt strong and it appeared to have zero issues. However, when I got it home, I changed the oil and realized that the oil was full of coolant. My first thought was waterpump. I changed the seals, but realized in the process that coolant and oil couldn't mix without it leaking out the weep hole. I then proceeded to tear down the motor. I split the cases and everything visually looked good. Except the new motor wasn't really new at all. (The seller is an A-hole and karma is going to destroy his life.) I took the cylinder and head to the machine shop and had them check for warping. The head was toast so I bought a brand new head complete with valves. I put everything back together with the new head and started her up. Everything seemed fine, so I decided to drain the oil to see if I fixed the problem. F my life... there was still coolant in the oil. I am not really sure what to do at this point. Any ideas? I've searched the forums but found nothing that I didn't already check.

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • grayracer513

Posted October 29, 2010 - 06:45 AM


The water pump cannot put coolant into the oil unless someone has plugged the escape port that is drilled under the pump in the crankcase cover. There's a gap between the oil seal and the coolant seal that vents to the outside specifically so as to prevent that from happening.

There are a limited number of places coolant can cross into the crankcase oil:
  • The O-ring at the joint between the crankcase cover and the crankcase.
  • The base gasket
  • The head gasket
  • Loose or missing jacket plug at the center of the head in the cam box (hex socket plug).
  • Cracked or porous head, cylinder, crankcase, or crankcase cover

  • dbreezy81

Posted October 29, 2010 - 12:50 PM


Thanks grey! I will double check the plug in the head. Maybe the new one didn't have one in it. I replaced all the other gaskets and the o ring. hopefully that solves it.

Related Content


Wilson the Blue Privateer by jetfuel

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  50 replies
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

BIGBORE FOR YZ450F 2006? by Taattie94

Dirt Bike   Make / Model Specific   Yamaha   YZ 400/426/450
  • 5 replies

The "going back to the other darkside" adventure... by Monk

Dirt Bike   Make / Model Specific   KTM   250/350/450/505 SX-F & XC-F (4-Strokes)
  • Hot  113 replies

James Stewart back on a YZ450F by YamaLink

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  47 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.