Gear oil grades

[Gray]

Just wondering how many are still using the 75W-90 gear oil as recommended by Nissan or for towing or because lab gear oil analysis isn't giving good wear numbers have started using a heavier grade of gear oil.

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[amr40509]

I'm using what the manual calls for. I went with Nissan suggested grades of Mobil 1 in the rear and Valvoline in the front. Did that at 30K miles. I have 45K miles on my '06 now and tow a boat every weekend. No problems at all so far.

[LittleStevie]

Unless you're a gear designer with a PhD in Mechanical Engineering, stick with what the Nissan engineers spec out in the manual.

[08Datsun]

This is something I had been recently thinking about. I still have the factory 75w-90 in there as I have only 8k. I've never had a tow vehicle that specified the thinner lube. I know that after the 2004 Titans started having rear end problems, they upped the spec from 75w-90 to 75w-140. My Grand Wagoneer also spec'd the thicker stuff for tow package models. Synthetic is spec'd in all of these.

Has anyone ever had problems with the R200? It's such a small ring gear you'd think it'd be overburdened. However, I haven't really run across any stories of problems so perhaps the 75w-90 is all that is needed.

[Gray]

Unless you're a gear designer with a PhD in Mechanical Engineering, stick with what the Nissan engineers spec out in the manual.

Problem with that is when the Nissan engineer spec'ed 75W-90 gear oil for the rear diff in 2004 or earlier he was using the old SAE designation which had a cSt@100°C viscosity range from 13.5 to 24 with most 90W gear oils being made at that time at the midpoint of about 18 or higher cst's, old designation shown in the following table;



Since Jan 2005 SAE came out with new J306 gear oil designations, as in the following table;

http://www.finalube.com/announcements/2 ... y_2006.pdf

...which downgrades the 75W-90 oil to a range of 13.5 to 18 cSt@100°C and since about 2006 most 90W modern gear oils being made in the midpoint of about 15 cSt's. There aren't many gear oils being built yet in the 75W-110 range but these might help with high wear metals showing up if one was doing in use gear oil analysis.

Here's an interesting white paper from Amsoil showing comparision of some 75W-90's and how various stand up in testing;

http://www.amsoil.com/products/gearlube ... Paper.aspx

Interestingly the new Amsoil 75W-110 has a cSt@100°C of about 20 which means it falls well within the old range designation of a 75W-90.

http://www.amsoil.com/storefront/svt.aspx

Somewhere I've seen some comparision charts of cSt@100°C related to oil film thickness which would give some further wear information.

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[Gray]

Lubrication Engineers also makes a straight grade 110W gear oil (#1605) which would work fairly well for anyplace that doesn't get much below zero;

http://www.le-inc.com/products/document ... _flyer.pdf

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