Should I flush my diff fluid?

I just got a 3.46 for my 323ci. The car it was on had some good mileage on (more than 100k).

Is it a good idea to flush it and change the seal while I have the diff in my hands and it's easy to work on?

I've seen diffs leak before so I'm wondering if this is something that happens often on high mileage bimmers or if I'd be wasting my time (and money).

BTW, I do track my car if this has any relevance.

I changed my diff fluid at 120k. I put Redline in. The old fluid smelled burnt. I haven't heard of many problems w/ the diff, but why not put new fluid in it since you plan on running it hard?

When I did my diff bushing I also changed to redline fluid. The old fluid looked fine, just a tad dirty, didn't really "flush" it, just drained the new, and filled with the old. Sediments from the last bit of the old were minimal.

Oh, when I changed my fluid I had well over 140k on it, and the PO made no mention of it ever being changed, so I'm assuming its the original fluid.

Why not while you have easy access to it.

I'm not really familiar with differential maintenance that's why I'm asking if it's worth it or if I'm good for another 100k and will have sold the car by then

Seems like a good idea to do it now, so I'll flush and put redline fluid in.

How about the seal tho? Should I replace it while I'm at it or is it extremely rare that a diff leaks?

For what it's worth, I just changed my differential fluid for the second time. I use Redline, and the old oil had darkened some and had suspended sediment visible in it. The last change was at 61K miles about a year ago, and I'm at 89K miles now.

There was also some staining on the outside of the seal area, so the seal may be leaking slightly, but it could also be dripping down from the rear suspension bushing. I would certainly suggest changing the seal if you've already cracked the housing open.

I'd change the fluid, but I wouldn't flush it. That seems unnecessary, and I'm always afraid of removing too much gunk from gearboxes. As for replacing seals, I wouldn't worry about that until they go bad...it's not terrible to do on the car.

Ok.

What type of Redline fluid is recommended for this?

You are supposed to flush your diff fluid every 30,000 miles or so.

Use Redline 75W-90

Originally Posted by frogg320

I'd change the fluid, but I wouldn't flush it. That seems unnecessary, and I'm always afraid of removing too much gunk from gearboxes. As for replacing seals, I wouldn't worry about that until they go bad...it's not terrible to do on the car.

+1

Don't forget to buy the fill and drain plug washers.

Thanks for the tips.

How much oil do I need?

It's cool, Redline is cheaper than OEM.

0.97 something, just shy of a whole bottle