I know it sounds silly at first glance, but I put about 3 qts
M1 75-140 in it about 3K miles ago, and it wasn't cheap like me. I never considered reusing a drained fluid before, but if it goes into a clean container ... then reuse it if it looks good?

 

Compare the cost of that oil to the cost of the gears. Then decide.

Ken

 

Your reply has a pithy ring to it, but it in no way addresses whether the oil is fit to use. Four quarts of the M1 is about $60, and if I can save that by reusing the fluid I see no reason not to do it, just as I would reuse a serpentine belt or spark plug that looked good.

PS - reason for this question is to install a locker

 

If you can afford new fluid buy new fluid. Yes the old fluid is problay good, but with all the handling something could have gotten into it and thats not good. Depending on how it was drained from the dif, like a 9" it runs out the front down the bottom of a dirty dif. I wouldn't use it. If out in the woods and I had to to make it back to civilzation I would use it. It's up to you.

 

nope i would not use it. just because of contamination. mobil runs 7.99 at kragen so look into that or RP www.kragen.com or www.karlracing.com

 

If you want to reuse it make sure to filter it with a fine screen. This may take some time though because the gear lube is very thick.

 

There are only two impurities that get in differential oil water and metal. If the vent system works and you don't see white oil I'd pour it thru a paint strainer with
a small magnet in it, and down the road we would go. Sixty bucks is too much to
throw down the drain.

 

I drained my diff and woudln't ever consider putting it back in. I then realized I hadn't done the seal right, so popped it again and redid it, the fluid that drained, that had been in less than a day and run one time, I tossed out.
I don't reuse ANY fluid, period. And I buy nothing but fluid from Ford. I don't want to have one of those episodes where the trannys or diffs freak 'cause they have some other fluid.
Don't reuse it. Might try cheaper fluid though, have no idea why you wasted that much money on it. I have no respect for your idea to be honest, you reduce your diff's life if you put that fluid back in, plain and simple. It's impossible for you to keep it perfectly clean.

 

... that the wisest course of action is to not resuse the oil. I'll probably have 5K or so on it anyway by the time I get the locker installed, and it doesn't add that much to the total cost of the locker install from a percentage standpoint. The possibility of contamination doesn't appear to warrant the risk, even if my sweetheart and I could have a nice dinner on the difference.

I must say, however, that the tone of certain responses was bothersome, and I don't believe I'm being overly sensitive. All sorts of folks ask all sorts of questions here, and when they're asked earnestly and submitted as a idea for feedback, there's no reason for disrespectful and insulting responses.
Consider:
I can think of many reasons to use M1 75W140 in my differential despite the higher initial cost; most have to do with the fact that I'll have an older truck heavily loaded with a 25 foot boat behind it a thousand miles south of the US border. I don't care whether you 'respect' my idea or not, it was just an idea whereby I might save a few bucks to spend elsewhere.

To those of you who left more thoughtful and considered responses, Thank You !!!

 

Your welcome, the only stupid question is the one not asked.

 

Sorry, I didn't intend to come off like that, I tend to deal with trans and diff fluid 50 gallons at a whack and it comes out of trans that generally cost what a pickup is worth. We reuse fluid all the time but we usually run it through a 20 micron filter buggy. Thats not practical with 3 or 4 qts but if you kept it clean while you drained it and then capped it, it should be fine for re use. You would be the best judge of that. Keep in mind that oil left in an open pan will gather a lot of airborn dirt and dust over a day or two. Especially in a shop where the doors are being opened a lot.

Hope your locker job went ok.

Ken