Help me determine good OCI for 2011.5 BMW M3

[dparm]

BMW's change schedule for the rear differential fluid is rather strange, and contradictory at times. In some documents it says every third oil change, which works out to every 45,000 miles. In other documents it says only cars with manual transmissions need the rear diff fluid changed, and that makes no sense. Confusing still is that some documents have no change interval listed at all.

The car is equipped with a GKN variable-lock limited slip differential. It's spec'd for 75w140 GL5 (factory fill is Castrol SAF-XJ/Syntrax Limited Slip).

The last change was done by the dealer two years/25k miles ago, which was the third oil change. Assuming the every-three-oil-changes schedule, I'm not due for another fluid change until around 75,000 miles, which is probably 3 years/25k away. I'm not sure I want to wait that long given my driving habits and the car's power.

Does an every-other year change interval sound reasonable? That would work out to about 15k-20k miles. As I said, I drive the car fairly hard and the LSD is utilized on a regular basis. I figure I could change it now and leave this fluid in until the next factory-required change in another 25k.

 

[95busa]

I run mine out 50-60K. I don't have an M3, but we are talking about trucks that pull heavy stuff often. I am about to change my F250 with royal purple 75-140 and upgrade to the 08+ finned rear diff cover. That being said, a quality 75w-140 is stout stuff. I have driven police cars 100K+ as hard as you can imagine in south Louisiana with OEM 75-140 with nary a problem. The only bad rear end I encountered was in a 1992 CVPI- before the 75w-140, it had 80w-90 as the factory fill. It had 130K plus though, and it kept going for 200k+, it was just noisy! So.... if a corporate Ford 8.8 can survive that, I have to think a BMW will be just fine.

 

[Doog]

I would definitely use Amsoil or Redline in the car and run it out 45k and do a used oil analysis. Then you will know for sure. I'll bet either would go 100k.

 

[Jeffs2006EvoIX]

In my Lancer Evo's I tracked I did the rear dif every 15k with RL gear oil. Never had an issue.

Try 15k changes. Hopefully it's something you can do yourself?

Jeff

 

[92saturnsl2]

I really don't see the need to go beyond the 45k recommended interval.

The differential in question is made to support the power under the hood- they're not made with the assumption that they will be driven by little old ladies or middle aged businessmen.

The factory fill is a top-tier, robust fluid. That fluid will not break down in 45k, you'd be more concerned with getting wear metal out with a fresh fill.

OTOH, if extra maintenance helps you sleep at night, with the annual mileage you put on, I wouldn't consider an every other year change to be excessive. But I'm confident the fluid will last much longer without any premature wear.

 

[INDYMAC]

Here's a novel idea, why not do a used oil analysis?

 

[fdcg27]

If you're concerned, change it more often.
Can't hurt and the quantity of fluid required won't cost much.

 

[901Memphis]

Sounds like you're already doing a fantastic job. Once every 20k is over kill if you ask me. Most of the wear in metals are long gone. I recommend a used oil analysis also if you want any kind of good guess. Make sure to get TBN and TAN.

 

[andyd]

In cars of yore, diffs were topped off and they generally outlasted the engine /body unless abused. I run Mobil 1 75 90 in the 528s. Every 75- 100k miles whether it needs it or not is the interval.

 

[dparm]

I was under the impression that due to the variable-locking nature of the diff, it would be much harder on the fluids.

In a straight line it operates like an open diff, but as the speed differential between the wheels increases, the clutches start to engage (increasing the locking factor). That sounds like it is going to wear down the gear lube more quickly. Yes?

I'd normally do a used oil analysis, but the time and hassle of getting the fluid out is not much cheaper/faster than just replacing it altogether.

 

[HTSS_TR]

The fluid is not too expensive but the hassle of changing it is the real problem, I would change both transmission and differential fluids same time at around 4th oil change or 30-35k miles in your case.

 

[dparm]

Originally Posted By: HTSS_TR
The fluid is not too expensive but the hassle of changing it is the real problem, I would change both transmission and differential fluids same time at around 4th oil change or 30-35k miles in your case.



$20/L, give or take, plus an hour of labor. Probably $100-120 out the door.

Dual-clutch transmission fluid was considered "lifetime" but I had it changed at 50k.

 

[barkingspider]

Use oem or a good quality fluid and u will be fine every 50k miles if not more.

 

[artificialist]

Originally Posted By: dparm
Originally Posted By: HTSS_TR
The fluid is not too expensive but the hassle of changing it is the real problem, I would change both transmission and differential fluids same time at around 4th oil change or 30-35k miles in your case.



$20/L, give or take, plus an hour of labor. Probably $100-120 out the door.

Dual-clutch transmission fluid was considered "lifetime" but I had it changed at 50k.


You can get the Ravenol equivalent for much less: http://www.blauparts.com/proddetail.asp?prod=J1D2111-B
I use it in my car, and it performs exactly the same as the OEM stuff.

What can be extremely costly is the price of the DCT filter. I don't know how much one for a BMW costs, but the Mitsubishi filter often sells for $100.

I changed the DCTF in my car, the filter was covered in metal. I did this at 30,000 miles, and I am extremely glad I did.

 

[Rendezvous]

I only have 10k on my E92 and have only changed the fluid one time so far. On my E46 M3 that I have put about 65k on I change it every 15K. Few track days on each run so that's why I stick to the 15k runs. On both cars I use Motul Gear Competition 75w140. Both cars for the most part have the same diff and I do not get any noise at all with them even on tight parking lot turns.

 

[Doug Hillary]

Hi,
dparm - The factory OCI recommendation is a good one, the Castrol lubricant (Castrol SAF-XJ/Syntrax Limited Slip) is right at the top of the tree

Castrol's transmission lubricants are excellent products - I have considerable experience with these (German origin) helping to tweak some of them many years ago
Their longterm success was discussed with Castrol's Rep (a BMW development exercise) at the Nurburgring 24Hr a couple of years ago

I also used them in my OTR trucks over millions of Kms with great results. I never changed the diff or gearbox lubricants inside two years or 500k kms

As a guide to using used oil analysis an increase in TAN of 2 over VOA is one point and a 20% increase/decrease in viscosity is another. An increase of Silicon to around 130ppm along with high wear metal number should also be considered as an OC factor

 

[dparm]

Originally Posted By: Doug Hillary

As a guide to using used oil analysis an increase in TAN of 2 over VOA is one point and a 20% increase/decrease in viscosity is another. An increase of Silicon to around 130ppm along with high wear metal number should also be considered as an OC factor



Doug, thank you for weighing in.

Could you explain your comment about silicon in more detail?

 

[Doug Hillary]

Hi,
dparm - Silicon (as an external contaminant) arrives there via for instance a breather. The level noted - confirmed as a contaminant - in association with elevated wear metal numbers indicates this is the likely cause of such numbers

Diff lubricants do deteriorate with time but IME the time factor depends on application. In my case with the OTR vehicles four years or so and 1m kms did not suggest via used oil analysis that the OCI was reached

 

[dparm]

Originally Posted By: Doug Hillary
Hi,
dparm - Silicon (as an external contaminant) arrives there via for instance a breather. The level noted - confirmed as a contaminant - in association with elevated wear metal numbers indicates this is the likely cause of such numbers

Diff lubricants do deteriorate with time but IME the time factor depends on application. In my case with the OTR vehicles four years or so and 1m kms did not suggest via used oil analysis that the OCI was reached



Thanks for the reply. I would be surprised if silicon can get into a differential. It is a closed system, after all, unlike the engine's crankcase.

What is most troubling is that BMW, the dealerships, nor the people who work there can seem to put forth a consistent message on maintenance intervals. It is a constant source of discussion on the various BMW owner websites.

 

[Doug Hillary]

Hi,
dparm - Don't be surprised about external contamination in diffs. there can be a number of entry points. The usual entry point is via vent/breather. In some cars the vent is plumbed into the boot or some other location