Mobil 1 Foam

[Eagle7]

86 RX-7 JY S4 engine.
I tried Mobil 1 15W50, and am getting some beige colored foam in the filler tube. Didn't have any issues using Redline 30W. Is it something with the oil, the viscosity, or is it just a coincidence and I've got a water leak somewhere?

Thanks,

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Marty Doane
ITS RX-7 #13
CenDiv WMR

[BrianB]

I believe your seeing moisture condensing at the top of the filler tube. When the engine cools down moisture in the air condenses in the engine,on the housing bottoms ,in the front cover. This moisture mixes in to the oil when you start the engine and kind of stays there until the oil gets hot enough to change it into vapor, It then rises up the filler tube and condenses at the oily top appearing as foam. Try removing the oil filler cap after a run to let the moisture escape!
Good luck!
BrianB
#70 ITS RX7 NER

[C. Ludwig]

It's pretty common in rotarys. I see the moisture no matter what oil I run.

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Chris Ludwig
08 ITS RX7 CenDiv