Torsen Diff oil change?

Technical Area Routine Servicing
2

No idea when the gearbox and diff oils were last changed.

I assume:

GL4/5 75W-90 semi synthetic for the gearbox (2 litres)

But what should I use in the Torsen diff, is 90EP suitable as in a standard unit and I it 1 ltr as well?

As usual many thanks in anticipation.

3

Same but it must be GL5 Mazda have never specified anything different for the LSD.

I can find no data to confirm that either basic mineral, semi or fully synthetic diff oil reduce wear compared to any other oil.

Unless someone on here can provide UOA data on a variety of GL5 oils.

4

The Torsen diff is basically a case full of worm and wheels - there is no clutch pack, so you don’t need a dedicated Limited Slip diff oil as far as I am aware. Specific LSD oils contain friction modifiers which are designed to help reduce noise from the clutch packs some standard limited slip diffs incorporate, where you can get clutch pack chatter (similar to wet brake squawk) if you don’t use a friction modified oil.

Use a GL-5 rated oil, as this contains more Extreme pressure additives (EP) and will provide better anti wear protection for this type of gear. Mineral, part or full synthetic should all be fine - but you will get better protection and performance with a full synthetic, or a part synthetic, compared to a mineral . You can also use a GL-5 limited slip oil in a non limited slip diff - the friction modifiers just don’t get used, but the oil will still lubricate fine.

You can go for a 75W-90, 80W-90 or straight 90.  Castrol Universal 75W-90 is a good all round part synthetic GL4/5, or Syntrax Longlife 75W-90 is a full synthetic specific high performance GL-5 axle oil for non LSD. If you have an LSD, or want to play safe because you don’t know - Castrol Axle Z limited slip 90 ( mineral grade specifically for LSD units requiring Friction Modifiers ) should be used - you can also use this in non limited slip diffs too.

You don’t really feel the benefits of a multi-grade in a diff - but you can do in the gearbox as it normally promotes easier gear changes when cold. This is due to the oil being thinner with a 75W-90 compared to an 80W-90 or straight SAE90 - allowing the gears to change easier.

Be careful with GL ratings for gearboxes though - don’t use a GL-5 where it specifically asks for a GL-4 under the mistaken idea it will give better protection - the additives can be aggressive to yellow metals and create issues with synchro rings so gear manufacturers will suggest the correct rating. If the manual says you can use GL-4 or 5, then you should be fine with either. And also - don’t use a GL-4 rated oil where it asks for GL-5, as there wont be adequate EP additive and you could end up with premature wear. a gear oil such as Castrol Syntrans Multivehicle 75W-90 ( GL-4 full synthetic ) will be ideal for the gearbox.

Hope that’s useful

1 Like
5

i replaced mine the other day 36k didn’t look like it had ever been changed when i drained it it had a metallic look so need doing i replaced it with

fuchs silkolene silktran syn 5 API 4/5 SAE 75W/90

synthetic racing gear oil for very high power outputs and hypoid applications.

seems to be working fine i used this as i had a 1 litre bottle left over from my toyota supra diff.

6

 

Knock Sensor,

If you compare a Used Oil Analysis of a gearbox and a diff.

It is not unsual to see aound 100 ppm of iron in the used gearbox oil. On the other hand 200 to 300 ppm of iron can be recorded in diff oil. I have also noted as you say a metalic sheen in drained diff oil.

 

 

7

Spokey,

I’m afraid that I have yet to see a set of used oil analysis that under controlled conditions show any reduction in metal content of used diff oil when various oils are tested that is oil described as mineral through to those described as fully synthetic are used. Therefore that the “protection” part of your statement seems strange and from what I can find is in the minds of the marketing departments of lubrication producers.

As always looking to be educated, therefore I would love to see data produced by an independent laboratory on named products under standard conditions to confirm your statement. Not interested at all in Motherhood and Apple Pie statements made by the lubrication producers or retailers.

There is also no legal definition available to define the difference between “semi synthetic and fully synthetic oil” therefore marketers are free to use these terms at will. Also a producer can use the words “mineral oil” to describe mineral oil with some synthetic content as in “semi synthetic”.

8

 

That’s cool, perfectly entitled to your opinion and preference - keep chugging the cheap stuff :slight_smile:

cheers

9

Thanks all for a most informative post.

As ‘Bluebell’ is almost 22 years old and I haven’t a clue what’s been in her diff for the last 19 of them I have opted for

EP80W-90 GL-4 Mineral Gear Oil 1L as it was on offer. Feel sure that it will see her out and probably me also, but hey only time will tell. 

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