Diff oil recommendations E46 M3

[andyy]

Hi there
I'm looking to change the diff oil in an M3 next week and was after some advice on what oil to use.
After some googling there appears to be 2 options.

1. BMW oil - the newer FM oil
2. Castrol LSD oil with Red Line FM fluid

Anyone got any thoughts on either of them?
Option 2 is my favourite as its cheaper - but I dont want to screw anything up for the sake of £30 - £40
Cheers Andy

[E30M3SE]

Either will be fine, even without the FM it will not cause any issues, the diff will just be a little noisier when going round tight turns at slow speeds, in carparks etc.

The BMW oil is Castrol oil.

[gaz1234]

just dropped mine off for insp2, using FM and castrol

[MMT]

I had option 2 in mine. If you go to the Opie site on m3cutters they're doing a deal.

[andyy]

Thanks for the advice - I think i'll go for option 2 then
Cheers Andy

[shibby!]

Get the BMW stuff, the new stuff with the FM booset.

I had a horrible grinding noise on tight left hand turns tuns before, so i ended up putting the castrol stuff in with the friction modifier...... Worst decision ever. It ended up grinding even worse both left and right, and not tight turns at all. The whole car would shudder.

Got rid of it for the BMW stuff, all noises gone almost right away.

[ant man]

shibby! said:

Get the BMW stuff, the new stuff with the FM booset.

I had a horrible grinding noise on tight left hand turns tuns before, so i ended up putting the castrol stuff in with the friction modifier...... Worst decision ever. It ended up grinding even worse both left and right, and not tight turns at all. The whole car would shudder.

Got rid of it for the BMW stuff, all noises gone almost right away.

As already posted. Castrol makes the diff oil. The standard diff oil contains a small amount of FM booster. Too much FM booster will render the LSD worthless and it won't lock up. BMW took the decision to only provide the diff oil and FM booster as a combo rather than in separate bottles back in July 2010. I only assuming but perhaps due to dealers putting the wrong bottle in and some ignorant owners putting complete and immediate quietness ahead of performance.


OP,
I'd recommend the separate bottles and only add a very small amount of Redline FM booster. Add it first after the diff is drained (before the adding the diff oil) so the exact amount added is known. Perform a number of full lock circles to force the oil into all the clutch plates. If there is any noise on tight turns and deemed unacceptable, then more FM booster can be added. Some links below.

Castrol Syntrax Limited Slip 75W 140 (formerly SAF-XJ 75w-140) fully synthetic and specifically designed for BMW differentials. BMW approved - API GL-5
1L = £12.52
http://www.opieoils.co.uk/p-736-castrol-syntrax-li...

BMW M approved tech data http://www.opieoils.co.uk/pdfs/castrol/BPXE-8F54WP...
Redline limited slip differential friction modifier compatible with synthetic gear oils - only add enough to eliminate diff chatter (grinding noise). Add a quarter at a time.
API GL-5 & GL-6 0.118L £13.18
http://www.opieoils.co.uk/p-6320-redline-limited-s...