You have no proof for your conclusion.
Generally all oils of the same type ar mixable. Or will your engine blow if you mix, just for example, Shell 5w-40 with Valvoline 10w-30? Surely not.
Both Motul Oils are rated for use in differential and transmission. My conclusion is that they have the same basic additive package. Make sense from a manufacturer point of view, saving production cost.
My guess is, the 75w-140 have added the aditional "blue" additive package. Maybe from VANDERBILT. Just my guess without proof, sure!

I will send Motul a Mail and ask them this week. Lets see if and what they answer.

 

I suspect you are not far wrong, and they will mix without issue and work fine. But still cant quite work out why the need to do this, the diff will work just fine on 75w-90 and will also work fine of 75w-140 as some feel the need to use.

Motul should reply to you no problem, but if you do not get the info you are looking for let me know as I can forward your questions on to my technical contacts at Motul.

Cheers,

Guy

 

I look forward to their answer too.

 

Download both MSDS pdf's (you need a email address) and open chapter 3 on both.
There's your proof.
Sure, the first 3 listed are the same for both although the quantaties differ. (90 - vs - 140)
CAS: 157707-86-3 (25-50% - vs - 10-25%
CAS: 68937-96-2 This is Olefinsulfid, an EP additive according to BITOG (2.5-10% - vs - 2.5-10%)
EC: 931-384-6 (0-1% - vs 1-2.5%)

But then...
The 75W140 also has this:
CAS: MIXTURE, it has the same EG description as the CAS: 157707-86-3 and is a mineral oil (1-2.5%)
and
EC: 939-591-3 (1-2.5%) with description:
REACTION PRODUCTS OF ALCOHOLS,
C14-18, C18 UNSAT., ESTERIFIED
WITH PHOSPHORUS PENTOXIDE AND
SALTED WITH AMINES
C12-14,-TERT-ALKYL

And you still believe this is all the same product?
So I did actually download the files and compared them, searched the web a bit to find what the CAS numbers mean and posted it here.
And what are you going to do?
Come up with yet another thing to convince yourself you're not depleting the sulphur based EP additive and you're doing it right?
Sorry for not sugarcoating it for you.

Motul is most likely going to answer in this way:
"Eventhough you can mix the oils and the mixture will flow (meaning it will not form weird chemical reactions and produce semisolid blobs of goo) we advise to use the product we have engineered as is to use the properties to the fullest"
Correct me if I'm wrong.

 

so i talked to mag hytech and i told them LE1605 doesnt spec for gl5 anymore and they responded

"After talking to LE they say the specs for GL5 have moved and will move again. It was a change in the specs that moved this product out of GL5.

We feel this does not preclude us from selling this for the applications we service. And yes I use it in my Truck and all the shop trucks."


So maybe because of the specs changed for for GL5 that this is still indeed the same product? basically they kept the same formula as previous and because of new GL5 specs it couldnt meet it ? so if thats the case it should still perform the same as what we have been using?




.

 

Thanks for the research you have done. Let's see if Motul's response is close to or way off from your prediction

P.S. I'm curious, do you still love your AD08R's or found something else as great/better?

 

Two (2) quarts of LE-9920 ordered from Mag-Hytec Thursday, 20 Sep 18. Delivered Monday, 24 Sep 18, by USPS. GL-5 hypoid gear oil. Enough for next month's differential oil change and one next year.

-- Chuck

 

let me know how it looks and feels compared to 1605 before putting it in the diff.

 

From what I could Google, it seems the GL-5 (ATSM-D7450) specs have not changed since 2013. So, it would seem like the LE-1605 formulation has changed.

https://www.document-center.com/stan...2013%20EDITION

 

Certainly there is a middle ground where mixing fluids has undesirable results that don't result in a catastrophic failure. It seems that is the concern being expressed with mixing oils being less than ideal.

No one is saying mixing fluids inappropriately is going to blow up your diff. But is it causing accelerated wear? Unless you do a before and after oil analysis you might never know.