Diff Fluid

[VMS Motorsports]

Filled mine up last night. put maximum pinion angle in it and got 3 quarts in there....I'd rather overfill, as stated before, keeps the pinion bearing lubed better..Amsoil 75-140 of course 

[thunder938]

3 q!!! wow 600 advises with the pick of a new car something like 1.1 qt.  I run just a bit more about 1.5 qts and have never had a problem.  With a locked rear there is alot less heat in the diff.  I have to change the gears every week for diff. tracks and I will run the same gear oil all year and have had no problems.

Red Line Shockproof Lightweight Gear Oil, 75W80, Synthetic...

My local  dealer also runs this amount and has had no prolbems in years and he runs 3 cars out of his shop.  We race on paved ovals..

[VMS Motorsports]

Theres no such thing as overfilling, and as stated earlier, if you put the max pinion angle in it and fill it to overflowing, the diff builder we use will guarantee it for a year...no warranty from 600 or its dealer network, so I'll go with recommendations from the guy who guarantees his work over the guy who wants to sell me more parts any day.. I dont switch rear ends at all during the season, dirt oval.

[Racinjj]

3 quarts seems a bit much, I am guessing that you filled some of the axle tubes.  It wont be an issue unless its starts coming out the breather.
I dont know how you can burn these gears up unless you ran it low on oil, not much power and not much moving in there.  I used the same 75w-90 synthetic all season last year and plan to put fresh stuff in this year and use it all season.  I will be changing gears after every race this year and will reuse the oil, I did the same in my late model and didnt have any issues.