Replacing Transmission and Differential oil in GRB WRX STI

The oil:
For gearbox/front diff and rear diff I use Motul Gear 300:

Oil Volume:

  • Gearbox and front diff: 4.1L
  • Rear diff: 1.1L

Requires 6L to purchase (or 4L can + left overs from last time), about $250 NZD for Motul Gear 300.

Before start make sure that car sits on four axle stands, and is levelled.
It is good idea to replace all the drain plug washers at same time.



Rear differential:

Relatively easy job.
Tools required:

  • Jack
  • 4x axle stands
  • 17mm socket
  • 19mm deep socket or 22mm deep socket
  • Hand pump or syringe like device

Assuming the car is already on axle stands and levelled…

To drain oil:

Remove drain plug (17mm bolt on the bottom).
Here is both drain plug and temperature sensor removed (used later for filling).

Here are plug and the sensor:

To fill oil:

Remove either 22mm nut with the sensor or sensor itself (19mm deep socket). I didn’t had 22mm deep socket so I removed the sensor. It is better to remove 22mm nut with the sensor as it is easy to over-tighten the sensor itself.
plug the drain hole and pump in the oil via temperature sensor hole, until it starts overflowing.
Remove the hose and let the excess oil drain.

Torque settings I use (found on internet):

  • 50Nm drain plug
  • 50Nm 22mm sensor nut
  • 10-20Nm??? sensor (not very tight!)


Gearbox and Front differential

A little bit harder job than rear diff…

Tools required:

  • T70 Torx bit (cannot do without it).
  • H10 Hex bit
  • 12mm socket
  • flat screw driver or some other device to remove clips (finger nails?)

Hand pump or syringe like device

Assuming the car is already on axle stands and levelled..

Remove the plastic guard (few clips and 2 12mm bolts at the front).
Although it is possible to change oil without removal (there is an inspection window), I removed the guard as it made easier to do so.

To drain oil:

There are two drain plugs, one for front diff (T70) and another for gearbox itself (H10):
Both of the drain plugs have to be removed.

Here are all plugs removed:

To fill oil:

Tighten both of the drain bolts.

Torque settings:

  • T70 Plug 70Nm
  • H10 Plug 50Nm

Unlike previous STIs the GRB STI does not have dipstick. Some might think this makes it worse, I think otherwise, as I don’t have to remove inter-cooler to change gear oil. To get correct amount of oil one must fill through side filler plug while the vehicle is levelled.
Here is the said filler plug (H10):

Using hand pump (or otherwise), oil is filled until it overflows through the filler hole:

another angle:

Once oil is overflowing remove filler tube and allow it to drain.
Tighten the filler plug to 50Nm.

Bolt/Clip on the plastic guard.

6 thoughts on “Replacing Transmission and Differential oil in GRB WRX STI

    1. iamroot Post author

      Here are Subaru part numbers for plug washers:
      803926070 Front (Torx plug)
      803918060 Pan (hex plug)
      803918040 Side (oil level)
      803920050 Rear Diff. (Drain and Sensor insert)

      As far as I know these are correct, best check with your local Subaru parts person.

  1. Adrian

    Thanks mate, I saw that some people also replace the sensor at the same time? Any recommendations on what oil to use?

    1. iamroot Post author

      No idea why you need to replace sensor.
      With JDM version the sensor is not really necessary as the LSD is of the Torsen/helical type. So if you have JDM GRB STI the oil is the same as for the front diff: any high quality GL5. I specifically use Motul Gear 300 75W90, and in the past with other vehicles (Celica GT4) I had used Castrol Syntrax 75W90.
      With other version that are fitted with friction type of LSD you will need to be careful as the oil needs to have friction modifiers for LSD to work properly. It is still has to be GL5 oil due to hypoid gear.

  2. Adrian

    Thanks I actually own a Euro spec GRF 2.5 STi, i will just go with your recommendation on using Motul, is your car a JDM 2000cc?


Leave a Reply

Your email address will not be published. Required fields are marked *