Gearbox / Centre Differential gear oil
Subaru Extra-S 75W-90 is a highly refined mineral gear oil. The gear oil is manufactured by a subsidiary of Shell in Japan and only sold in 25L drums. Extra-S is not only made to Subaru specs but is the factory full in the gearbox / centre diff and rear diff for the WRX. Whille Extra-S is not sold in Australia, I import it by the litre from U.S.A. The gearbox of the WRX is really fussy so don’t use a fully synthetic gear oil or you will differently get grind. Since this oil isn’t synthetic I would change it more frequently. Extra-S doesn’t like the cold so don’t use it is you live where is snows. I change this gear oil every 25,000 KM.
Rear Differential gear oil
Motul Gear 300 75W-90 is a fully synthetic ester (grade 5) gear oil. This oil works very well in the cold and hot temps. Gear 300 handles the heat really well which is important since the rear diff is small, only taking 0.8L or 1L for Australian models. Gear 300 lowers the noise of the rear diff compared to OEM Extra-S. Since this gear oil is designed for rally / track use I would change it more frequently. I change this gear oil every 25,000 KM.
Engine oil for Winter
Motul 8100 X-cess 5W-40 is a fully synthetic POE (grade 4) engine oil. I change this oil every 6,500-7,500 KM. Personally I be leave the oil change interval of 12,500 KM for a turbo charged Subaru is far to high. I use an engine oil with a 5W to help with the cold starts in the morning (4*C to 4*C). I’ve had good results with this engine oil and will continue to use it next winter. This fully synthetic engine oil with multiple manufacture approvals performs very well and I highly recommend it. I use an OEM Subaru oil filter.
Engine oil for Summer
Motul 8100 X-max 10W40 is a fully synthetic POE (grade 4) engine oil. I began using X-max to combat my thermal stress causing shearing issue I had when using X-cess during summer. With multi-grade SAE oils, the broader the SAE numbers the more viscosity improver needed. In a engine oil with a very broad multi-grade SAE such as 0W-40 or 5W-50, more viscosity improver is used. Viscosity improver (VI) is often the first component to degrade in fully synthetic oils, well before the base oil degrades. I use a 10W-40 SAE to to help with the hot summer days (28*C to 45*C with an average of 32*C). I change this oil every 8,000-9,000 KM. On paper this oil is very close to the specs of Shell Rotella 5W-40 full synthetic which has been raved about on most U.S Subaru forums but isn’t sold in Australia. I use an OEM Subaru oil filter.
Engine oil for Track Days
Motul 300V Chrono 10W-40 is a fully synthetic ester (grade 5) engine oil. This is a racing oil and should be used as such. I wouldn’t recommend using it for daily use as it lacks the amount of detergents normal engine oils would contain. Before a track day I would dump out the existing oil and fill it with 300V. I change this oil every 5,000 KM. The use of an ester base stock means the oil will be able to withstand high engine temps without shearing. I would recommend using a pink STI oil filter when using this oil.