WRX diff oil

[tom]

I'm looking to change the diff oil to a synthetic as it gets really
cold here. I've checked past posts and a lot of people seem to prefer
the Redline 75W90ns. Now, I've read the info on Redline's website and
they state the the NS is for non-limited slip diffs, though it is GL5.
Shouldn't I go with the straight 75W90 though?

 

[David & Caroline]

With the RedLine synthetics, you would want to use the 75W90NS in the
transmission (it's less slippery, and is better for the synchro's) and can
use the regular 75W90 in the rear differential - they are both GL-5 rated.
(realistically, either one is probably fine in the differential - the
limited slip part is sealed from the rest - it isn't lubricated by the gear
oil you put in there)

 

[Edward Hayes]

I looked on redlines site and some of their gear oil is listed as GL4. Be
darn sure you use a GL5 rated oil. eddie

 

[David & Caroline]

I looked on redlines site and some of their gear oil is listed as GL4. Be
darn sure you use a GL5 rated oil. eddie

As long as you stay away from the MT90 and MTL, you are fine.

from www.redlineoil.com

75W90 Gear Oil - the preferred product in nearly all car and light truck
differentials, both conventional and limited-slip. 75W90 is preferred for
most racing applications. It contains friction modifier which is recommended
for limited-slip units. 75W90 Gear Oil can be used in many transmissions and
transaxles; however, other Red Line lubricants have better frictional
properties for rapid synchronization. Exceeds API GL-5.

75W90 NS - a GL-5 which does not contain the friction modifiers for
limited-slip hypoid differentials. This makes the transmission synchronizers
come to equal speeds more quickly, allowing faster shifting and much easier
low-temperature shifting. Can also be used in racing limited-slip
differentials where weak spring design causes too much wheel spin.

80W140 Gear Oil - generally used in commercial trucks which will climb long,
steep grades and some racing applications where power is not critical.
Generally 0.5% less efficient than 75W90. Can also be used in differentials
and transmissions where excessive noise is a problem and limited-slip
differentials which vibrate excessively when turning a corner. Exceeds API
GL-5.

LightWeight Gear Oil - a 75W/80W GL-5 gear oil designed to lubricate
transmissions and transaxles which recommend 80W GL-5 gear oils. It has
excellent low- temperature flow which allows easier shifting when cold. Also
has good synchro compatibility. May be used to obtain maximum power transfer
in racing differentials which do not see high temperatures.

SuperLight Gear Oil - a 70W/75W GL-5 gear oil with the viscosity of an ATF.
This is used when temperatures are not high and when the maximum power
output is required such as in qualifying laps.

ShockProofTM Gear Oil - a unique lubricant containing a suspension of solid
microscopic particles as an extreme pressure agent. The viscosity
characteristics allow the lubricant to resist throwoff and provide a film
thickness greater than an SAE 250 grade, with the same low fluid friction as
with our 80W140. Recommended for offroad racing and problem gearboxes.

MTL® - Manual Transmission/Transaxle Lubricant. A 70W80 GL-4 gear oil which
is designed for manual transmissions which require 70W - 80W GL-4 gear oils,
motor oils, or ATFs. It provides low temperature shiftability equal to an
ATF, yet will not thin out or shear at high temperatures and provides the
substantial gear protection of a GL-4 gear oil. The higher synchronizer
coefficient of friction allows faster upshifting and downshifting and the
lubricant is non-corrosive to synchros and bushings.

MT 90 - Manual Transmission/Transaxle Lubricant. A 75W90 GL-4 gear oil which
is designed for manual transmissions which require 75W90, or 90 GL-4 gear
oils or motor oils. Uses the same chemistry as MTL , but is a 90 WT in order
to satisfy certain manufacturers which recommend SAE 90 GL-4 gear oils.

 

[tom]

Thanks, but I looked up Cobb Tuning and they recommend the MT 90 for
gear oil. Highly even. I wonder how much of a difference there is
between GL 4 and GL 5. I tried emailing Redline, but all of my emails
got bounced back. I wonder if they're going to update the MT 90.

 

[blazing lazers]

I had the same problem with redline, no answers to emails. I ended up
with Amsoil because I drive mostly highway.