How many miles can you go before you need to change the diff's and crank case fluids? In my Range Rover i change my diff's around every 30,000 w/ Lucas 80/90 gear oil.

If you believe BMW (apparently Supersteve does), the fluids are lifetime fills. But the rule of thumb is to do it between 60k-100k miles.

Got the new plugs in...no more leaks! Apparently, BMW uses two types of plugs on the diff, one with crush washer and the other with built-in O-ring. My original plugs required a crush washer as there wasn't an O-ring built-in.

Not sure what I said to warrant that statement; but, since you brought it up.:stickpoke

The gear oil is a life time fluid. It doesn't go through the heat cycles nor is it exposed to the combustion contaminants that engine oil is. BMW uses synthetic oils everywhere in there vehicles. The only reason to change diff oil is if it becomes contaminated or your looking for something to fix.

138,000 miles on my 2001 4.4 and I haven't changed it yet.:thumbup::thumbup::thumbup:

This was your statement that I was :stickpoke
Don't want to start an arm wrestle here. If you feel that there's no need to change out those gear oils, then by all means drive it until those units fail and swap in new ones.

For the record, those diffs and transfer case DOES go through heating cycles. Try putting your hand on the diffs after a good drive. Although, it doesn't get exposed to contaminants such as those in engine oil; the contaminants that it does get exposed to are within the gears themselves. You'll always get metal shavings anytime there's metal-to-metal contacts (synthetic may reduce it, but not eliminate it). Worst yet, there's no filter of any type in there, so the gears just get bathe in their own filth until the fluid is changed.

Again, if you believe BMW on their lifetime fluids, then you gotta ask yourself the question: Why would BMW offer to change out all the driveline fluids (engine oil/filter, transmission, and differential) at 1,200 miles on all M cars? So what gives? Are the rest of the cars that BMW makes use far superior parts than M cars that does not required the initial break-in fluids change?

FYI...BMW used to recommend break-in fluids change on all their cars at 1,200 miles until they introduce the "Free Scheduled Maintenance" program. The Lifetime Fluids happen to get "invented" at the same time.

I changed all of my driveline fluids at 90K. The transmission fluid was black and the pan had a thick coating of sediment. The transfer case and differential fluids looked like new (and I reused the original drain plugs).

To start, my first comment made no reference to BMW's lifetime fluids claim. It was a simple suggestion that you may have over serviced your differential.

secondly, Yes all fluids in vehicles go through heating cycles; however, the heating cycles of engine and auto trans fluids are far greater than those of transfer cases and differentials. As the oils in the engine and trans circulate they heat up and cool down. Resulting many heat cycles during the normal operation. The tranfer case and diffs heat up while you drive and cool down when you stop. One heat cycle during normal operation. Additionally, tolerances in the engine and trans are much tighter than the tranfer case and differentials which results in much higher temps (not to mention the combustion process adding heat) and much thinner oil viscosities.

I find your statement regarding metal to metal contact interesting. The purpose for lubricants is to prevent metal to metal contact and for cooling of these parts. If you have metal to metal contact things stop rotating quickly,IE spun bearings, locked gears, ect.

The purpose for BMW or anyother manufacture to offer "break in oil changes" can be for many reasons:
1. Some manufactures use straight weight oil from the factory.
2. The vehicles may have been made 10 months before you purchased it (even BMW suggest you change your engine oil a minimum of annually)
3. During the manufacturing of the vehicles, although they try, not every single part is as clean as it can be. Some metal shavings may make it through the machining process and wind up in your engine, trans, diff what-ever the case may be.
4. There may be a need for a break in period.
5. Customer satisfaction.

Life time fluids is not something new and neither is not having break in oil changes. My 1988 Mustang GT came from the factory with the engine pre-run on a dyno and broken in as do most engines produced since then. You would have to ask BMW why they did, but don't now, perform break-in oil changes. My guess at there answer would be something to the effect of. . . "it's not needed." I'll bet they will change your fluids if you want them too.

They may have changed the manufacturing process of their vehicles or the quality or manufacturer of lubricants may have changed. Mobil 1, for example, has undergone several reformulations in the time it has been around. It is still a synthetic oil, obviously, what changes are all of the additives they put in the oil.

Heres a tid bit to ponder: The oil cap on my 2001 4.4 says "use only BMW synthetic oil" which at the time was made by Moble 1. The oil cap on my 2006 4.4 says "BMW recommends Castrol."

Times change.

DKL:

No arm wrestle here either, but a couple of comments on your unscheduled maintenance justifications.

I haven't seen a history of X5 differential failures. Lacking that data, what would cause one to not believe the lifetime fluid recommendation? This is a gear lubricant, in a sealed system.

The gears don't get bathed in their own filth (interesting turn of phrase there). The metal particles go to the magnetic plug in most cases.

M cars use mineral oil in the engine, not synthetic, from the factory. That is the designated break-in procedure. It is likely related to the cylinder honing procedure followed during manufacturing. That is why there is a 1200 mile oil change. Not sure on the logic for other fluid compartments, if in fact they get changed as well, I don't know.

Your Free Maintenance conspiracy theory would only apply in the US, where all fluid changes are covered. The rest of the world, who constitute the majority of BMW sales, and who got the longer maintenance intervals, did not get free maintenance, in general. The common denominator for all countries is that BMW pays the warranty costs, and holds the lease residuals. I will believe there is a problem when I see a history of failures. No significant failure rates reported yet.

Also, the fluids recommended today bear no resemblance to the fluids recommended when the vehicles were new. My new BMW model uses an API engine oil designation that is much improved over the original API specs when my X5 was produced.

Anyway, I agree with Supersteve. I also believe that if one wants to change their fluids early, they should do so. There isn't a mechanical reason to do so, but there is a feel-good reason. That should be sufficient justification. I wouldn't say that the diff fluid change recommendation is 60-100k, it is in fact lifetime. If you want to do it early, do it whenever is convenient; one interval is no better or worse than another.

Reading JCL, SuperSteve and, a couple other very
knowledgeable posters here, is an absolute treat, imo.

They know their tech/mech stuff, are common sensical about
it, and offer worthy advice and opinions, imo.

Just wanted to express my Ks&As for their posts...
Best Regards, mD

Cheers Motordavid and JCL!