Diff fluid out breather tube?!

Yup , everything expands with heat , gearing , bearings , the diff casing etc etc . A quick way to figure it out ,,,fill to the bottom of the fill plug when cold , then check after a test drive when hot and I will bet its going to be almost overfilled

 

Yeah makes sense, dont like the idea of foaming & bubbling (air pockets) tho...

 

Yes and yes. How all us rednecks out this way still do it. It can be a bit low, so long as you get a dot on the tip of your finger,, pinky finger allowed,,for us club fingers(allowing for slight knuckle bend),,all will be well. About 3/4" below the fill hole,,give or take. Going on 15yrs with this truck setting them up like that,,no severe venting or overheat to date.

Ever seen a gearbox spun up with a view window installed?. It's a Mixmaster in there set on rat nasty puree. It can't help but foam up a bit. Thank god it has anti foam agents in it. Oil is flung hard against the case when its spun up, splashing off the wall, back onto the gear set,,repeat.