LE1605: I called Lubriction Engineers when I noted the GL-5 notation was missing on the bottle. Customer service referred to an engineer who noted (1) the formulation had been changed (?) and (2) regardless they no longer had any means of testing for GL-5 standard which requires something like an Oldsmobile engine from the 1970s. :) Anyway, long thread elsewhere with some recommendations.

Differential oil shoundn't be too thick as it lubricates by splashing oil from the lower part of the housing onto the gears and bearings. If it's too thick it won't splash when cold. Multi-grade oil will solve that problem. I have couple year old LE1605 in my differential right now that's scheduled for replacement next month but I've not decided what to use even though I bought a couple different oils.

-- Chuck

Not all differentials are created equal, I'm not sure ALL rely on splashing of the oil from the bottom. In ours, there's enough oil in there where the bottom of the ring gear rotates in the pool of oil at the bottom, bringing oil up to the top of the diff where it can fall down onto the other gear train in there.

When he said splashing I understood that to simply mean that the oil had to 'splash' down off the ring gear to lube everything else. Hence uber thick, cold oil would not do that very well.

Not that it had to splash 'up' from something wacking into it (like the little splasher on the bottom of connecting rod on an old Briggs and Statton lawnmower).

Here's a short video of of lubrication in a differential. All differentials lubricate in the same way with the ring gear splashing lube over everything inside. Differential case interior structure includes channels to assist this. (This video is part of a series on aftermarket differential covers and explains how they're often just "truck bling" on the back end.) Excessively thick lubricant will not have the same flow patterns until/unless the temperature gets high enough.


Viscosity grades are confusingly different among different oil types. Everyone (I hope) is familiar with SAE Crankcase (engine) oil grades. They're much different for the same viscosity gear oil.

SAE 90 hypoid gear oil, as specified for the differential spans the viscosity range of SAE 40 thru 60 crankcase oil. LE-9920, a multigrade 75W-140 GL-5 gear oil spans the range from 10W to more than 60 crankcase oil and includes gear oil 90 in the range. I'm thinking, though, that a 75W-90 might be ideal since I don't expect the differential to approach engine temperatures.

-- Chuck

Chuck after that big discussion on gear oil, my moms neighbor has an s2k and we always talk etc and were discussing gear oil etc i showed him the post and what he ended up doing is he talked to mag hytec and they told them they use the new stuff in all their trucks etc that spec for gl5 with no issues. but anyway he ended up getting the "new le1605" for his MY05 as well and has 5k miles on it with no issues so far. hes gonna change it out at 10k and ill report back. @Chuck S

Been using 75/140 in diff for years. Its my preferred as well as Puddy Dads in this car.

Keep in mind though that the oil also has to be thick enough to be sufficiently picked up by the ring gear and moved, in enough quantity to provide adequate lubrication. I would not call this splashing so much as it being moved, or pumped, by the ring gear.

An old-time mechanic told me that as gear oils go, the differential needs lube which will not breakdown. And will continue to flow, under high heat. As the nature of how a differential works is much different than the how the gears work in a transmission. The diff generates more heat than a transmission, under normal operating conditions.

Yeah there is little in the way of splashing, but rather its the ring gear being partially submerged carrying the oil. Thicker is actually better to a point. Also creates more cushion/film strength on a glass diff such as ours.

The diff is one area where thicker fluid tends to correlate with lower wear. When I noted the cold temp thickness it is likely perfect for 3 season use, I would not use it in cold winter conditions if one was to drive their s2000 in winter weather. Above 32 F should be okay.