s2000Junky

Because 3 "ear" shaped metal piece from some shim came out with the oil when draining. I sent pics to puddydad and he advised me that it was from one of several shims that have 4 ears and that to just keep a lookout for more metal chucks on next shorter interval change and recommended I run 75/140 as he does with all his diffs. I switched as mentioned 35k ago and diff still going strong, no more metal parts. Its seen the track a handful of times in that period too. I was running the typical 75/90w. Don't remember brand, was a long time ago. Likely mobil 1 though since im an off the shelf guy generally.

Billman250

I too have found the ear shaped pieces during dif service. None of the difs ever developed problems.

Mobil1 is a great choice, I have watched it perform wonderfully in countless S2000s over the years.

RolanTHUNDER

Oh snap! This will be the first diff oil change I will do so I will keep both eyes out for any metal pieces and sincerely hope I find none.

RolanTHUNDER

Thanks Bill. Mobil sounds really good. I have the Liqui Moly 85/90 pictured here so I'll give it a go for several months then maybe drain it to see if anything other than oil comes out. If so then I will strive to get 75/140. Not my daily by the way so she doesn't see traffic or many miles but I am going to track her soon.

RolanTHUNDER

Good points. The climate where I live is mostly warm. Even in winter we rarely see colder than 10 degrees celsius during the day. I don't daily my S2K and she doesn't see traffic. I got the car with a crappy 4 puck in the drivetrain but I got rid of that less than a month into ownership. Now I run an OEM clutch. Bear in mind I'm boosted so she puts down a lot more power and torque to the wheels than stock and my diff is stock. No strange noises at all though. I do need to upgrade my diff mounts sometime this year. I have absolutely no idea which oil weight is in there now because the previous owner has no clue - he gave it to someone to fill up for him. Must be 75/90.

As for driving habits, I haven't tracked yet. I do drive fast but not necessarily dumping clutch every single time and in every gear or stand still launches - haven't launched in a long time TBH. I drive it like an S2K is meant to be driven but with great respect of course
So based on all the above I really do desire the best protection I can get from any fluid, engine, gearbox, LSD.

SpitfireS

Yeah, I had to
Lets start with the owners manual. That's always a good start.
What does it say (in my 1999 manual) regarding differential oil?
SAE 90, API GL5/GL6 (page 198)
What does this mean?
SAE 90 is a single grade oil.
Is it the same as a multigrade 75W-90? No, it is not, for more than one reason.
Why?
Reason 1:
Because multigrade oils have additives like pour point surpressors or anti thinners or whatnot.
Those additives, needed to get the 75W-90 label, are not lubricants and they break down under mechanical stress.
An oil without them is a stronger, more stable oil.
This is not an opinion.
Reason 2:
In 2005, SAE changed the J306 gear oil specification and added SAE 110 and SAE 190.
SAE J306 - Automotive Gear Lubricant Viscosity Classification Engineering360
This is an important fact.
For the S2000 it means the SAE 90 from 1999 was most likely a much thicker oil than today's SAE 75W-90.
I say "most likely" because we have no hard data.
There is some supplementary info in the manual though: the API GL5/GL6 recomendation.
API GL6 was a gear oil spec that never became official but was intended for high offset & high loaded hypoid gears.
What is a high offset hypoid gear set?
It means the pinion gear is well below the center line of the ring gear.
This configuration allows a diff with the output shafts closer to the bottom of the diff for better ground clearance.
It also creates a hypoid gear set where the gear teeth slide a lot over eachother.
Oils that have to deal with this need to be thicker to provide the film strenght.
Please note that there is not pressurized lubrication in a diff, it all relies on film strenght (not like in engine journal bearings where the rotation itself creates oil pressure)
In my opinion, it is not overreacting to say the 7" ring&pinion set in the S2000 is high loaded and it has a high offset for sure (just measure it)

Now, combine the facts and opinions (educated guesses):
Today's equivalent for SAE 90 diff oil is NOT SAE 75W-90 but SAE 110.
People that want to use this are just following their owners manual with modern products.
If you have trouble finding it (or you just don't want to go through any trouble) 75W-110 is the next logical choice.
If you can't find that either (or if you don't want to look for it) the safest step is a step up: 75W-140.

If parts start falling out of your diff it is trying to warn you: you're doing something wrong here!
Please don't ignore it.
Especially not when the solution is an easy one: use an oil better suited to the diff.
And with that were back at the owners manual.

Chuck S

Duolec 1605 is a SAE 110 API GL-5. Meets the spec for our car taking into account the new SAE 110 appears to be the former SAE 90. Critical part is this is GL-5 gear oil.

$18 to $25 an oil change is not excessive.

-- Chuck

HarryD

I was waiting for you to reply -- I thought I covered you on Post #2:

SpitfireS

You clearly did not understand what I wrote.
Your loss.
I sincerely hope you feel happy and comfy with your 75W-90.

P.S. are you one of those alternative facts people?

HarryD

You're right, for the super anal and OG category, I mistakenly listed LE 607 (SAE 90) which I believe was replaced and should have listed LE 1605 (SAE 110) instead, per your tirade of a post.