Will you be tracking your car? And how often do you plan to change fluids?

 

"The diff" is two parts, the final drive and the Torsen LSD.
According to Torsen the LSD will funcion using ATF fluid but the final drive in the S2000 certainly DOES NOT (maybe for a kilometer).
The OEM recommendation is for the final drive, GL6 is an absolete spec and was intended for high offset hypoid gears.
And guess what we have in the S2000?
High offset hypoid gears have the pinion gear relatively far away from the center of the ring gear, this results in a lot of sliding between teeth, it closer to a worm gear drive.
GL6 was never actual as GL5 gear oils at the time increased their film strenght enough to cover for GL6.
Is any GL5 good enough then?
Well... not for a long time.
Multigrade oils tend to shear and because of the high offset gears this happens even more so a thinner oil to begin with with end up too thin after a while.
Add, what was already mentioned, that in 1999 SAE 90 could be almost as thick as current SAE 140 as there was no step in between 90-140.
And add that the OEM SAE 90 was a single grade oil.
I do remember posts of people showing parts falling out the diff drain, they were thrust washer 'ears', and they never noticed anything from the diff in how it acts.
There were posts saying "Oh yeah, I've seen this before, it's no problem, the diff still works"
All those people were using 75W90 diffwater because it's soo easy to find.
Sure, it's your car.
The diff oil does also plays a role in how the Torsen locks.
I've mailed Torsen about this (long time ago) and they confirmed and also said (as was mentioned here) I would not notice it.
But I did, and do.
Take a tight turn, low speed, get on the throttle a bit half way through (no drifting) and if the front pushes out your Torsen can't handle the wheels turning at different speeds.
Or, better said, it can handle it but the locking bias has changed.
Fresh diff oil will fix this.

So in short:
Yes, diff oil is important.
Stay close to the original SAE 90 and NO that's NOT 75/80W90, it's better to use SAE110 or 75W140.
You can get Amsoil in the Netherlands and not for the prices posted.
But in the very end: it's your car.

 

This is the wrong place to save that small amount of money. You don't need super expensive Amsoil or the crazy priced Honda stuff.
I'm using Castrol syntrax longlife in mine and I didn't pay much more than 15 euro for that.
Like stated before, Honda recommendations translated to today's spec would be SAE90-110, if you think a 75W-140 seems too thick then mix it up with some 75W-90.

About the transmission fluid, I'm not sure MTF3 is really a mineral but it's know to break down during hard track use so I wouldn't be surprised if it's true.

Show us any brand oil that has the same cold viscosity on both 75W-90 and 75W-140, I have never seen it and I highly doubt it exists

 

thanks for this info! Very informative. I will stay away from the 80w90 and go for something like the 75 or 85w140. But first of all, where can i find the amsoil cheaper in netherlands??? I think that is what you suggested.
About the front push, i have some questions.
My front pushes wide if I accelerate mid corner, but especially at moderate and higher speeds. Like long bending turns on the highway, if I accelerate during those long curves my front pushes out and I dont feel comfortable accelerating. It doesnt give confidence. And i see regular cars passing me...

At low speeds the nose grabs well and turns true the corner tightly, and turns better with some throttle.

If I enter a moderate corner at say 50 kmh steady speed and start to accelerate midcorner it pushes wide as well.

If I would enter the same corner at higher speed lets say 60-70 and let it roll into the corner off throtle or just a tiny bit I will go midcorner about 50, and if I accelerate then the car behaves better and doesnt always go wide at the front. It seems to have a tighter line like equal what the steering input is.

is this behaviour normal, or am I doing something wrong? Or could the diff be involved on this?

i hate the front going wide (understeer i guess) because it kills confidence! In all scenarios I described of the front going wide in a turn under accelerarion, letting of the trottle the front immediately dives into the corner. Making a sharper turn, but loosing acceleration. Accelerate again and its going wider again.

please help!
at any given speed, especially noticeable except low speed.

 

Hi no tracking. Only spirited driving, no granny driving haha. Lots of vtec, not sure if that relates to the diff as well.
Changing the least possible, without bringing problems to the car! Can the diff be filled with only raising the rear of the car? That would make it much easier, less hasle. What do you recommend? Thanks

 

I found the castrol syntax 75w140 but it says Limited Slip. Is that a problem? Or is that what you use as well?

 

The Limited slip additive is not a problem but it's not needed for our type of LSD.
This is what I use, 50/50 mix in a empty pear lemonade bottle

 

SAE90 fom the year 2000 is SAE 110 Today? Huh?

I am reading a lot in dedicated Oil forums (BITOG..) but i never noticed this.

Where could i find this Information?


EDIT: Found it. SAE 90 has a kinematic viscosity range form 13,5 to 24 at 100°C back then when the owners manual of the S2000 was printed.
Revised in 2005, SAE 110 was additional introduced. SAE 90 is now 13,5 to 18,5, the new introduced SAE110 range is 18,5 to 24.

Cougar Lubricants International Ltd | SAE Viscosity Grades For Gear Oils

So, SAE 90 and SAE 110 are fine today, but thicker is better.

 

The diff on this car is one component that generally shows lower wear with higher viscosity fluids pretty consistently. Not pushing any fluid but going thicker should protect better in warm weather conditions. I never drove my car in winter so I don't know if that holds true in winter conditions.

 

I like to compare stuff so I made this table with a few different and commonly available (in Europe at least) diff oils.
Maybe interesting for others as well