12valve@heart

I like the heavier weight too so I cheat and run Castrol Syntec 5w50 synthetic overfilled by one quart.

pwrtripls1

Well you cant go wrong by splitting the 2 and putting in some Royal Purple 20W50 motor oil. Its right in the middle, plus in a HD trans I like the royal Purples 400% more film strength than the leading competitor. Makes me feel warm and fuzzy.

jmd025

5 qts of Mobil 1 5w30 here. Save your gear oil for rear ends and T-19s.

EClancy

your not driving a semi truck...your driving a 3/4 ton and/or 1-ton pickup truck. those transmissions/rear ends work alot harder than yours do, for many more miles than yours do, much more often than yours do.

the factory recommended fill is 5-30 motor oil...why not use it?



92 ghostrider....if i had to deal with your transmission guy....i'd run the other way

Alwaysworking

if they use gear oil because it can stand up to the abuse why shouldn't i use it?

EClancy

your not "abusing it". your not hauling 80,000lbs+, your probably not driving 500+ miles/day, your not shifting 10-18 times before you hit 50 mph, your most likely not putting 2000+ft/lbs of engine torque through your transmission.

your moving around a 6000lb truck, and whatever trailer you may or may not hook to it, 5-30 is more than sufficient

jmd025

I think the answer to this is that the bearing tolerances in the Getrag are so tight that they require a certain weight oil for PROPER lubrication, and the recommendation for that is 5w-30. You can go with synthetic to increase thermal protection some, but gear oil is gonna be too thick in my opinion.

Josh

93beater

ok well by being a member of this site for quite a while i have learned just do what dave says, he knos his stuff! im about ti buy anohter 6bt with a getrag and ima gona run 5w30 syn in it. its what ur truck calls for. our trucks also call for diesel fuel only, idk about ya'll but i use what it calls for.