Coastal 75w-90 vs. Castrol Hypoy-C

[Narcoleptic]

I was looking for a 75w-90 gear oil to do a flush on my '96 Subaru Outback before swtiching to synthetic. Now, normally I would just switch but this transmission had recently been split apart for a re-seal. Subaru manual transmissions have a center differential inside the transmission case and the transmission and differential share oil, so I thought a GL-5 was required.

The only two 75w-90 oils I could find were Coastal which is rated GL-3, 4, and 5. The other was Castrol Hypoy-C which is rated only GL-5.

The Castrol bottle stated it was for "service fill" of limited-slip differentials. The Coastal stated it was only to be used for top offs of limited-slips. This is a significant issue, as if the oil has friction modifiers for a limited-slip, the syncros don't like it.

I chose the Coastal oil, but the wording of the Castrol bottle left me wondering. Does "service fill" in Castrolese mean drain and refill with no friction modifier needed, or just top offs?

 

[Drew99GT]

Service fill probably means it has the required friction modifiers for limited slips.

I have tried about every 75w-90 out there for my Corollas 5 speed manual, and Castrol Hypoy C GL-5 feels and shifts by far the best, even better than Redline

 

[weatherdude]

quote:

---

Originally posted by Narcoleptic:
I was looking for a 75w-90 gear oil to do a flush on my '96 Subaru Outback before swtiching to synthetic. Now, normally I would just switch but this transmission had recently been split apart for a re-seal. Subaru manual transmissions have a center differential inside the transmission case and the transmission and differential share oil, so I thought a GL-5 was required.

The only two 75w-90 oils I could find were Coastal which is rated GL-3, 4, and 5. The other was Castrol Hypoy-C which is rated only GL-5.

The Castrol bottle stated it was for "service fill" of limited-slip differentials. The Coastal stated it was only to be used for top offs of limited-slips. This is a significant issue, as if the oil has friction modifiers for a limited-slip, the syncros don't like it.

I chose the Coastal oil, but the wording of the Castrol bottle left me wondering. Does "service fill" in Castrolese mean drain and refill with no friction modifier needed, or just top offs?

---

If you have Mystik lubricants in your area, the JT-7 80w90 Gear Lube would be a good choice (better than the costal, and most likely cheaper too.. I can pick up the Mystik at around 1.10 to 1.50 a qt here).

Here's the specs: Mystik JT-7 Gear Oil (PDF FILE)

Of course, if you don't mind spending some more for an even better lube, give MolaKule a yell at his company, Specialty Formulations. That way you get a great lube and support a BITOG site sponsor as well!