2004 350Z tranny and diff fluid change
 

2004 350Z tranny and diff fluid was changed 16k and 5 years ago. Is time a factor when fluid should be changed?

Thanks.

I change it once a year. That stuff is pretty viscous and exposed to less heat than motor oil. The main thing you'd flush out is any metal particles that come off of the internals over time. By the way I just hit 190k and my tranny is doing great. Currently using Royal Purple.

I literally changed my oil, tranny oil, and diff oil today. They were dirty and black. I just got the car a year ago. I should've done it earlier. The diff magnet had a lot of junk on it and so did the tranny but I have the 3rd gear grind so. Car drives like brand new though. I suggest changing them for the peace of mind. It's very easy. But you wouldn't damage anything without it.

Hopefully, everybody doing this tranny and diff change has researched the difference between GL-4 and GL-5 lubricants and used the respective fluids required. Tranny and diff oil should never appear "dirty and black" unless that's the color of the lubricant that went in there when it was fresh. Both systems are sealed and not exposed to ongoing combustion or dirt, and while there may be some wear of moving parts, there should never be a LOT of "junk" on the drain plug. If there is, either something mechanical is wearing heavily, or the lubricant isn't doing its job well!

No hate or anything but you're telling me that gear oil should look exactly the same when you drain then from when you put new in? Every YouTube video and friend that has changed their diff and tranny fluid has had a dark brownish color to it. Everyone should know the difference between GL4 and GL5. When I say dirty I dont mean literal dirt. It just looks wore out. 350z and G35 cook diff oils. The LSDs get very hot. It's normal to get a bit of shavings on the drain plug. I tracked and drove my beater 300zx hard and never drained the diff oil the same color as I put in. Kept it for 4 years and never once blew the diff. Am I doing something wrong?

I never said any gear oil should look exactly the same when you drain it, as when it was brand-spankin' new. When I drain Redline MT85 from my race or street Zs, the well-used lubricant comes out as a clear and red-tinged fluid. When the Motul GL-5 fluid comes out of my Nismo LSD, it's dark blue, almost the same color as when it was first installed. I use another GL-5 fluid for my VLSD in the street Z and it comes out as dark amber, but never "dirty and black".

My point is, unless you're severely overheating your diff or tranny, the color of the used lubricant shouldn't change much. We have a lot of new Z owners on this board who don't know much about the specs; some have even put GL-5 fluids in both their tranny and rear ends! But going by color alone won't tell much about the condition of either the tranny or diff. You'll need a dedicated UOA for that.

Maybe it's the frequency with which I change mine. But last time I changed it, it was clear enough that I questioned whether or not it really needed to be done.