Rear Differential Oil Foamy/aerated

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Apr 24, 2009
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Yesterday I checked the rear differential fluid in my Tacoma. When I pulled the plug, the oil seemed pretty foamy/frothy/aerated. I had just drive the truck about 5 miles on the highway prior to pulling the plug, so it wasn't sitting very long. I checked it this morning without having driven in and it was normal without all the bubbles in it. Does this seem like a problem? Doesn't seem right to me and has me a little worried. I would think there should be no air bubbles in it.
 
It's normal. Gear oil can be whipped up by the gears pretty fast. There are some videos on youtube of people who have put on clear differential cases. You can see it directly. The oil starts out fine, and within a minute it looks like a frothy milkshake. This is normal. There are anti-foam additives in GL-4/5 to keep it from getting out of control.
 
Originally Posted By: Steve S
There is going to be bubbles. The oil is whipped up by the gears turning in the oil.

Exactly.

Some oils trap more or less air than others, but some aeration is completely normal.
 
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