What's the best condition to change diff fluid?

Warm? Cold?

Basically I have a diff that I got from a yard and I'm prepping it to be installed on my truck. Can I change the diff fluid ass it is now since it has been sitting? Or would it be a wast of gear oil and should I wait till I install it and do it after I drive it and mix it all up? Dot would it be good if it was changed now while all the nasty has settled to the bottom?

 

Huh? Don't you need the pumpkin to be drained for the diff swap to take place?

 

nope i have the whole axle im swapping. sorry for the confusion.

 

Don't run it with the current oil. If it was me I would change it before you drive it and then change it again after a hundred miles of so, to be sure you get all the gunk out.

 

x2. just put in 2 quarts, go inside and drink a beer while you let it run down the axle and settle, then put in the last quart.

 

ok guys thanks for that info. i will be straining the old diff fluid as well to check the condition of the gears, what is an acceptable amount of metal shavings to have in a diff that has around 65k miles on it and is most likely on its factory fluid?

 

lets say 1/8th to 1/4 of an inch on the magnet. it will be kind of pasty like a thick lotion cause the bits are so fine. if it's a lot more than that or there are full metal chunks is when you know there could be a problem.

 

It was about an 8th or quarter inch and like a metallic past just like you said. The pluid was black and no big pieces. Thanks for the info guys