nester

Which differential oil should I use for the stock GS430 '01?

Manual says "SAE 90" (or, below 0F - "SAE 80W" or "SAE 80W-90").
Basically I have here (it's not that much choice here, eh..) only Castrol Regular (SAE 80W-90) or Castrol Syntec (SAE 75W-90).
Which one should I use? Is "75W-90" same as "90"?

nester

OK, found some RTFM: http://www.substech.com/dokuwiki/doku.php?id=gear_oils

SAE Designation of gear oils by viscosity
The Society of Automotive Engineers (SAE) established a viscosity grading system for gear and Engine oils.

According to the SAE viscosity grading system all oils are divided into two classes: monograde and multigrade:

■Monograde gear oils
Monograde gear oils are designated by one number (70, 90, 140, 250, etc.). The number indicates a level of the oil viscosity at a particular temperature. The higher the grade number, the higher the oil viscosity.
Viscosity of gear oils designated with a number only without the letter “W” (SAE 80, SAE 90, SAE 140 etc.) was specified at the temperature 212°F (100°C). These gear oils are suitable for use at high ambient temperatures.
Viscosity of gear oils designated with a number followed by the letter “W” (SAE 70W, SAE 75W, SAE 80W etc.) was specified at the temperature 0°F (-18°C). The letter “W” means winter. These grades are used at low ambient temperatures.

■Multigrade gear oils
Viscosity of gear oils may be stabilized by polymeric additives (viscosity index improvers). Viscosity of such gear oils is specified at both high and low temperature. These oils are called multigrades and they are designated by two numbers and the letter “W” (SAE 75W-90, SAE 80W-90, SAE 85W-140 etc.). The first number of the designation specify the oil viscosity at cold temperature, the second number specifies the oil viscosity at high temperature.
For example: SAE 85W-140 oil has a low temperature viscosity similar to that of SAE 85W, but it has a high temperature viscosity similar to that of SAE 140.
Multigrade gear oils are used in a wide temperature range.


Now viscosity is clear - any suggestions about brand and should I choose regular or syntetic?

jz4203

Everyone has their own opinion but I've been using the Mobil 1 Synthetic 75W-90 with no issues. When changed out after using Mobil 1, I've seen no metal filings.