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LSD Oil Change Time - Liqui Moly 85/90?

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LSD Oil Change Time - Liqui Moly 85/90?

Old 03-05-2017, 12:22 PM
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Overkill always works ( super anal and OG ). We're talking lunch money extra cost (one lunch) every 30,000 miles or two years (book maintenance). But why not skip two (2) lunches and do it annually or every 15,000 miles?
-- Chuck
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Old 03-06-2017, 01:31 PM
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Originally Posted by SpitfireS View Post
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.
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.

I am in this camp.

unrelated, but noteworthy is that you can prevent pitting in the cv cups by using thicker cv grease like redline or valvoline synthetic. the OEM grease is like water and the cups will pit.
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Old 03-06-2017, 01:32 PM
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i disagree that spitfires logic is overkill and super anal. i believe it is the minimum requirement for better diff protection.
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Old 03-06-2017, 02:34 PM
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Was the original spec'd oil likely conventional?
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Old 03-11-2017, 01:33 PM
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What I would like to add: the Torsen LSD will like a SAE 110 or 75W-110/140 better too.
Imagine the steering column is a cable reel and there is a cable connected with the throttle.
The more you turn the steering wheel the less you can push the throttle down and vice versa.
So halfway through a turn when your steering returns to straight, you "unwind" the cable and you can push the throttle down further and further and accelerate out of the turn.
If at that point the front won't stay into the turn, like understeer, I would say your Torsen is acting up.
Because both rear wheels have grip but rotate at different speeds: that's the way a Torsen diff creates lock.
But in this case you don't want lock: it will make the inner rear wheel push the front out.
The oil has to deal with that.
At some point I asked this question via the Torsen website and they replied that oil plays a small role in Torsen lock bias.
The Torsen will live on thin oil, even on ATF as far as they claim on their website back then (maybe they still do) but thinner oil, with less film strenght, will change the lock bias.

For me this all started in 2006, about a year after I bought the car.
I remember the car changed behavior and I went to a Honda dealer and asked if they could check the electric power steering and/or alignment.
When I picked up the car the next day they said they only changed diff oil and the behavior changed back to normal.
That Honda dealer used SAE 90 GL5 used in the Honda Marine outboard motors (the hypoid gears that drive the prop).
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Old 03-14-2017, 04:17 PM
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I use amsoil 75w-110 based on research done on this site.
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Old 03-14-2017, 06:01 PM
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Advance auto parts has 75w-140 Mobil 1 for $14.99 6 blocks away. I put my pan under the diff, take off the fill, then the drain bolt, then ride my bike to the store, and have a coffee down the street, and by the time I get back, it's all nice and drained, then just fill'er up. Don't even have to jack up the car, just slide on down there, since I'm not a tub of lard.
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