Best Diff Oil?

[BristolE30]

Hey zone,

Got a bit of a whine coming from my diff after doing an auto to manual tran swap. It's only in first and second, then it fades away.

Anyway I've been advised that a diff oil top up/replacement could help. What is the best oil to use? Happy to pay a little extra if its quality.

Cheers,

[BristolE30]

Sorry forgot to mention is a normal open diff

[Lemon98]

If it's only in 1st and 2nd that would make me think the whine is from your gearbox, mine is also kinda whiney but nothing excessive, is a getrag 240 on a 320i with open diff. I also recently replaced my diff and gearbox oil with those linked below and I'm happy with them.

I'm not an e30 expert my any means have only had mine a few months but I went from the recommendations in my Autodata and Haynes manuals looking for modern-day equivalents and also the composition and properties of the oils to make my decision. They're good brands and good quality I'd say for our application. (I did chemistry at A level and am studying motorsport engineering at uni so have a fair idea of what the words mean and characteristics I want)

(1) Diff Oil: https://www.opieoils.co.uk/p-972-fuchs- ... 0w-90.aspx
(2) Gearbox Oil: https://www.opieoils.co.uk/p-722-castro ... x-oil.aspx

[Lemon98]

Also to follow that don't bother with just a top-up. Replace both oils fully with new ones, it's not a difficult job and the diff only takes 0.9l anyway.

[biffer]

My Getrag 260 also has noticable whine in 1st and 2nd, had assumed 'they all do that'.
Road-tests of these ,when new ,mention gearbox-whine in lower gears.

[boiliebasher]

I would check gear box oil level too just to be on the safe side

[BristolE30]

I would check gear box oil level too just to be on the safe side

How do you check that?

Yes planning on doing the full drain and refill on the diff. Wondering if there’s anything I can add to help reduce the wine

[BristolE30]

I went for some Castrol Diff oil 80w-90. Do you think this will be okay? I know people has specified 75w-90, but summers coming?

Cheers

[Lemon98]

I went for some Castrol Diff oil 80w-90. Do you think this will be okay? I know people has specified 75w-90, but summers coming?

Cheers

I'll show you what my repair manuals say later today as am going out to work on the car (replacing diff mount bush with poly) and both books are in the garage.

I went with 80w-90 I think you'll be absolutely fine

[Lemon98]

I went for some Castrol Diff oil 80w-90. Do you think this will be okay? I know people has specified 75w-90, but summers coming?

Cheers

Also in my opinion the fact that it's a mineral oil and not synthetic is more important than it being an 80w vs a 75w. If you take it easy on the car while everything's warming up then we won't have any problems at all. And we don't have clutch plates that could wear out with the wrong oil either so to really fuck up the diffs we would have to use something completely inappropriate.

[Lemon98]

IMG_20200403_120432.jpg

80w-90 is equivalent to SAE 90

*this is from the owner's handbook btw

[HenryM3]

From an interest point of view, I have temperature sensors in the diff and gearbox, in normal everyday driving it takes ages 20+ miles before they even register heat. A little less miles if pushing on. Neither seem to be under much stress, perhaps if you spend you driving time sideways and maxing your 0–60mph times it would be a different story.

[Lemon98]

From an interest point of view, I have temperature sensors in the diff and gearbox, in normal everyday driving it takes ages 20+ miles before they even register heat. A little less miles if pushing on. Neither seem to be under much stress, perhaps if you spend you driving time sideways and maxing your 0–60mph times it would be a different story.

Factory sensors or did you put them in and are you using an aftermarket ECU to measure the temps or just extra gauges?

Just asking out of interest as any data is cool and I'm into that sort of thing as a motorsport engineering student. But I deffo don't go sideways with my open diff and don't push the car for at least 15-20 mins anyway.

[HenryM3]

No not factory, just modified drain plugs with sensors, wired via switches to the engine oil temperature gauge on the instrument cluster.

08E6F93C-C75F-4C93-9E55-44FA916BD8C0.jpeg

The lit up switch is reading g/b temperature. If that switch is pressed the one on the left lights up and your now measuring diff temperature.

[martauto]

No not factory, just modified drain plugs with sensors, wired via switches to the engine oil temperature gauge on the instrument cluster.
08E6F93C-C75F-4C93-9E55-44FA916BD8C0.jpeg
The lit up switch is reading g/b temperature. If that switch is pressed the one on the left lights up and your now measuring diff temperature.

Mart.

[Lemon98]

No not factory, just modified drain plugs with sensors, wired via switches to the engine oil temperature gauge on the instrument cluster.
08E6F93C-C75F-4C93-9E55-44FA916BD8C0.jpeg
The lit up switch is reading g/b temperature. If that switch is pressed the one on the left lights up and your now measuring diff temperature.

Huh that's a really cool way of doing it I like you ability to switch between them like that!! Very cool

[BristolE30]

Changed the diff oil and added a small amount of Ceratec in but alas the whine is still there. I think it’s the pinion bearings inside the diff, so it’ll have to a rebuild!