Oil for differential gears

[Azraelo]

Hi!
I've got a Chinese light truck, in its rear axle differential service manual it says "Use 85W-90 GL4 oil". In the repair shop I have 80W-140 GL-5 oil, so I decided to use it. The enviromental temperatures here is around 30° C average so I think the viscosity difference is not an issue. Since there are not "yellow metals" such as brass or copper in the diff, think it will be no problem with GL5 instead of GL4.

Please your comments and suggestions about my decision.
Guess I'm still learning.
Thanks!

 

[TheBlacksmith]

Unless you are addressing a known problem with a systematic approach, following the manufacturer's recommendations is always a prudent course.

 

[romke]

i do not see a problem that you use a GL5 lubricant in stead of the prescribed GL4 in this particular case.

replacing the 85W-90 viscosity with a 80w-140 is a different matter. a 85W-90 can be regarded as a 90 with a guaranteed low pourpoint, the viscosity at operating temperature will hardly differ from "just a 90".

a 80W-140 however is a less temperature sensitive oil that includes a viscosity index improver to make it less prone to viscosity change when the temperature varies. that means that in actual service it more or less behaves as a 140 oil with a much higher viscosity then the manufacturer anticipated or deemed necessary. it also means operating temperature may well be higher due to churning losses resulting in a somewhat higher fuel consumption. thus, the oil is more viscous and that may also lead to problems with foaming.

if a 80w-90 is unavailable i would rather prefer a 90. it will be very hard to find a 80W-90 GL4 anyway, most if not all of the available 80W-90 oils are GL5, whereas most of the GL4 oils are 80W.

 

[RossABQ]

NAPA or Farm/Fleet stores carry "odd duck" oils in Gl-3, and -4. Not clear if you are in the US or China? Farm machinery from as far back as the '30's is still in use and lots of them need older spec lubes.

 

[drwebb]

GL-5 is for more severe service than GL-4, in some cases having exactly 2-times the same EP/AW chemistry. So if the GL-5 claims yellow metal compatiblity (as most modern ones do) then I would consider it generally 'backwards compatible.' But the viscosity is significantly higher than recommended, as others have noted.