350i Gearbox Oil

[adam quantrill]

Going round the circle again, I was using SMX-S a few years back and agree it's pretty good. But then I converted to the Mobil 1 and it's just that much better, far more consistent when really cold, or really hot.

[andymadmak]

adam quantrill said:

Going round the circle again, I was using SMX-S a few years back and agree it's pretty good. But then I converted to the Mobil 1 and it's just that much better, far more consistent when really cold, or really hot.

Didnt you have a gearbox failure with the mix? ( apologies in advance if I am mistaken)

[adam quantrill]

I've had a few fail over the years. Latest one was in the 400SX when the box had emptied itself of oil, there was just a dribble left in there. That was Mobil 1 and Moly mix and frankly I am amazed it lasted with so little oil in there.

[Rsedmonds]

Hi all,
I’m just about to change my gearbox oil so decided to do some research before I dived in, and boy I’m glad I did. There seems to be a lot of passion behind using ATF, dedicated gearbox oil and engine oil with an additives.
So being as honest as you can could you tell me whether the route you chose to go was a good one? Are you still using the same oils now as discussed in this thread? And how many miles you’ve clocked up using what you choose?

Regards Rob

[andymadmak]

Rsedmonds said:

Hi all,
I’m just about to change my gearbox oil so decided to do some research before I dived in, and boy I’m glad I did. There seems to be a lot of passion behind using ATF, dedicated gearbox oil and engine oil with an additives.
So being as honest as you can could you tell me whether the route you chose to go was a good one? Are you still using the same oils now as discussed in this thread? And how many miles you’ve clocked up using what you choose?

Regards Rob

So long as you don't use ATF (or similar), you can pick from either of the other options and get a good result.
My personal preferences are either Motul 80 (it's what the gearbox was originally designed for) or Castrol SMX -S. (much easier to get and just as good) I did a lot of miles in my Wedge and never had a problem.

Rover (actually BL) really dropped the ball when it made the switch to ATF at the launch of the SD1 and it's amazing how many people still use this oil, especially in the high power/torque applications of the gearbox. It's about as useful as water when the going gets tough!

[Rsedmonds]

Cheers for that, Motul 80w90 is going to be the 1 I think, would you put any moly slip or similar in with it?

[andymadmak]

Rsedmonds said:

Cheers for that, Motul 80w90 is going to be the 1 I think, would you put any moly slip or similar in with it?

I'd go with the 75/80. No additives required.

[KKson]

On both my old 350i and current 390SE I went for the gearbox flush and then the Adam Quantrill recommended Mobil 1 with molyslip additive. I've been more than happy with gear change etc and have run that combo for 6 years now without any issues.

I've just changed the gear oil on the SEAC for the ultra expensive Difflock Evolution 1. It may well not be related but I'm struggling with gear synchro when I try any fast gear changes. It could be that the gearbox synchro is just knackered but I'm going to put some old thicker Dexron 2 in it as a trial, just to see if there is any difference.

Edited by KKson on Tuesday 19th May 11:05

[KelvinatorNZ]

I'm glad this discussion sees sense. The FB group is so quick to dismiss anything except ATF or the difflock fluid, which is silly.