D360, you are mistaken that more gear oil is better for the differential. So rigging up a system to allow yourself to run the gearbox overfull is backwards thinking.

The fill plug was designed into the casting by the guys who designed the differential. They put it at the right place.

Cold, you fill the diff with the pinion level to where you can stick your finger in and just feel the oil below the threaded hole. That'd be about a half inch down. When it gets warm it should just start running into the threads.

That is all the oil that's needed for the gears to live. Adding more oil than the optimum amount may cause foaming and if you drive long enough you'll find out that having foam trying to lubricate hypoid gears isn't a good idea.

Because your gear oil contains an EP additive that sticks to the gear teeth the surfaces will be protected, but it's better to rely on liquid lubrication rather than the surface lube provided by the Extreme Pressure chemicals.

R.