As far as I remember the Gear 300 75W-90 doesn't have this additive.
It, according to Mr. Matchbox, also doesn't smell like rotten eggs.

I don't want to quote original Motul part of the API GL-5 answer because it will be out of context.
What they should have said, IMO, is that the Gear 300 being GL-4/5 is not a problem for our GL-5 diff - in THEIR opinion - as it IS GL-5.
They make it sound though, at least to me, that GL-5 is backwards compatible with GL-4 and as far as I know it's not.
Because of the slipperyness so synchro's don't work well, as you mentioned, and the possibility the phosphorus based EP additive in GL-5 oils is not by default safe to use around yellow metals (and no, our diff doesn't have any)

It would have been nice if the Direction Produit Automobile would have mentioned the SAE J306 change, being the addition of SAE 110 range.
But then the Direction Produit Automobile would have to admit they don't have this particular viscosity in their product line-up.

 

Excuse me?
The MSDS clearly shows the 75W-140 uses additional EP additives.
The rotten eggs.

 

I've asked Motul direct for their thoughts on it, not that anyone should be using the Competition 75w-140 in an S2000 gearbox for normal use. The additional additives could be for the ls side of things, I haven't looked too deep into that particular oil but I will. Either way, it still will not eat yellow metals found in a synchro, Motul's own description of the 75w-140

All hypoïd differentials with limited slip system, gearbox with integrated limited slip differential, mechanical transmission, synchronised or not synchronised gearboxes, transfer gearboxes operating under shocks, heavy loads and low revolution speed or moderate loads and high revolution speed.

Technically GL5 is backwardly compatible to the GL4 as a GL5 will pass all the tests required for GL4. How many GL5 oils are sold as a GL4 because of this? Now in the real world or is it internet world, there have been reported issues of GL5 oils causing problems with shift in a gearbox originally recommended GL4 but depending on who you speak to... This could be highlighting a potential component issue already within the gearbox. A bit like the motorbike synthetic oil vs wet clutch mystery. Who knows, has anyone had any direct experience of this?

The viscosity change from 2006 is a non issue, they also capped the viscosity of an SAE140 and introduced an SAE190. So SAE90 was capped at 5.5cst (not a big change in viscosity) lower when they changed its upper level from 24cst to 18.5 but that, to a torsen diff as found in the S2000 makes no difference as most SAE90 oils were not at the top end of this bracket but somewhere in the middle. I have asked Motul and others if they changed their SAE90 viscosity when the change was brought in and if so by how much. I am expecting the answers to be no, or by very little and translated to the real world, no difference in performance.

I would suspect Motul do not have a SAE110 as they see no practical application for it. Or not enough to warrant making one. As I said in my post earlier all these oils companies and their techie people apply their knowledge differently.

Cheers,

Guy

 

That’s the smell of EP additives which are sulphur compounds, similar to rotten eggs which are hydrogen sulphide, also a sulphur compound. Most gear oils will smell pretty similar. But the fact remains the same, to achieve GL4 and or GL5 the technology and the additives to do this are one of the same. I have the additive provider data sheets (the additives purchased by the oil manufacturers) for this right in front of me that clearly show its the same technology, sadly I am not allowed to post them on the internet.

Cheers,

Guy

 

All this deep technical info on lubricants is very enlightening. Appreciate all the knowledge being dropped here by several obvious subject matter experts.

Also appreciate the way the dialog is going! Disagreements that are staying civil. A sense of respect that the other guy knows some stuff, and everyone trying to really hear what the other is saying.

Stay classy lubrication thread...

 

The "conscience of S2KI" speaks...and I agree

 

If the 'it is not safe for yellow metals ' statement turned into an internet myth, just like the 3k mile oil change, I'm happy to drop it.
I went by what I read on the interweb , not just the first hit on Google, but still.
Most will never use those kind of gear oils in a modern manual transmission anyway, as mentioned, because pretty much all car manufacturers have their own MTF oils.

What would be interesting to know if Motul ever (lets say, around 1998) had a single grade SAE90 in their product range, formulated to meet GL-6 (!) and what viscosity it had.

The Holy Grail of questions would be "What viscosity did Honda have in mind with SAE90 GL-5/6?".

On the other, based on my own experience, hand:
No matter what anyone says I could use, I will never use / recommend anything under SAE110 for an S2000 diff, even an OEM one.
Sure, you could say "Oh, but I change it every 5000km so I can use the diff water", and then you should as it's your car.
And if you then find LSD parts on your drain plug you can fool yourself a little more and think "Ohh... but that's not a problem at all"
Even if, IF, those 'ears' are only used during the assembly of a Torsen, to keep the side washers in place before the circlip axles are put in, I would not like them to show up on my drain plug.
But that's me.

 

Just for information, one of the few SAE 90 GL5 Oils:

https://www.ravenol.de/produkte/verw...e-90-gl-5.html

Its not a synthetik.

 

The yellow metal thing has been going on for years, since the late 60's. That is how long that one has been doing the rounds. The additives used that did cause harm to yellow metals were dropped in the late 1960's by reputable oil companies so it is just a non issue these days. Even if you get an oil to score a 1B on a copper corrosion test it is fine, and going to do no harm to anything.

I am curious as to why you are so interested in API GL6? It is long obsolete, I only have one that even mentions GL6 here https://www.opieoils.co.uk/p-68903-f...-diff-oil.aspx Last time I spoke to Fuchs about API GL6 was back in 2008. GL6 was intended for high offset hypoid drives where very high loads were imposed on the gears. There has not been an application for it for many years, hence API have not maintained it. The performance exceeded that of GL5 by some way. There are no referenced (calibrated) test sets, so no one can prove an API GL6 performance of an oil.

What Fuchs did was to put in around twice as much additive (sulphur/phosphorus) and they say this gives them GL6 performance, their additive supplier backed them up on that based on "technical judgement". This has a use in motorsport where heavily modified engines can impart very high loads on unmodified drivelines.

I am sure Motul once had one.

I still think you are trying to engineer out a problem that does not exist by using SAE110. The quality of the oil will have a bigger bearing on the protection it gives more so than the viscosity. So, you could get an SAE90 that can do a better job, take more heat and resist shearing down more than an SAE110, and visa versa. Quality is the key. You also refer to SAE90 as diff water when it is anything but, I am still waiting for confirmation but the change in 2006 to viscosity just didn't really change anything as far as the S2000 diff is concerned. Oil manufacturers were not suddenly massively reducing the viscosity of SAE90 oil as most of them came in at 18.5cst or below. The other issue is the viscosity gap, say between 75w-110 and 75w-90. It will require more viscosity improvers to bridge the gap between 75w-110 than 75w-90 and viscosity improvers shear down with use, the more you have the more prone to shear it is. Technically it can be argued 75w-90 is more stable, and an SAE90 even more so again. This is why 0w-50 engine oils don't really exist because of the amount of viscosity index improver need to make it, a 0w-50 soon becomes a 0w-40 and so on.

Cheers,

Guy

 

Monograde SAE90's will be mineral, multigrade 75w-90 oils will usually be semi synthetic or fully synthetic.

Cheers,

Guy