wr400 air bubbles in motor oil?

7 replies to this topic
  • spike2kx

Posted December 06, 2011 - 12:19 PM


just recentaly had a wr400 that had a top end rebuild done has only been on test rides. but when i check the oil it has turned soupy because of air bubbles. need help on where and what to check.... thanks in advance

  • ur2silly

Posted December 06, 2011 - 03:46 PM


Are you sure it's air or is it liquid? Does the oil look like pancake batter? Is so then it's more than likely fluid in the oil usually indicating a leaking gasket.

  • spike2kx

Posted December 07, 2011 - 07:54 AM


ya its air bubbles. we put some of the oil in a cap to see if it would seperate with water but no water or any liquid..just tons of air bubbles

  • ncampion

Posted December 07, 2011 - 09:03 AM


Possibly overfilled with oil or the oil is not returning to the tank. The spinning crank can "froth" the oil if there's too much left in the crankcase. That's not a good thing BTW, as it does not lubricate well with a bunch of air bubbles displacing the oil. Need to check it out before riding much.

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  • spike2kx

Posted December 07, 2011 - 09:17 AM


Thanks ill check it out right now....ill let u know what I find

  • troy306

Posted December 07, 2011 - 10:37 AM


Try switching to a different brand of oil, and make sure you do not over fill. I had the same issue, and switched to different brand of oil, and bubbles went away.....

  • ur2silly

Posted December 07, 2011 - 10:45 AM


I would not run the bike until I found out what the problem is because of risk of damaging the engine. Even at idle the crank turns a complete rvolution about 33 times every second. If anything is not being lubed properly it has potential to fail very very quickly.

Are there any visible oil leaks anywhere? If so you might start there.

There could also be a tiny leak on a hose or gasket somewhere (possibly an area with vacuum) that is letting air in but no oil can get out.

Make sure oil level is correct. If it's too low it will cause the oil pump to suck air and mix with whatever amount of oil it is pumping. If oil level is correct after the bike sets for a while perhaps an oil return route is blocked not allowing oil to return back to the oil pan quick enough. This would cause the pump to pump the oil out of the resevoir faster than it returns causing the symptom of low oil level.

Cheap oil will foam more because of poor anti-foaming additives.

Check very carefully and make sure there is absoulutely no sign of oil in the coolant. Does the bike overheat?

Here is something else I read:
'Bubbles' in the oil are not good. Usually, they're not air bubbles, but water droplets. When you see them, it's a sign that your oil is contaminated with water and needs to be changed. A more serious problem is how the bubbles got there. Quite likely, there's a leak between the system that circulates oil (to lubricate moving engine parts) and the system that circulates coolant- the water 'jacket'. Could be something relatively simple, like a blown head gasket, or something really ugly- like a cracked head.

  • Krannie McKranface

Posted December 07, 2011 - 07:16 PM


Try some better oil and see what happens.


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