according to the manual i'm only supposed to run SAE 90 gear oil in my GSL-SE differential and was wondering if this was the correct oil since a) couldn't find it in any store in austin and b) i'm ordering from what looks like an industrial supply site. anyway, here's the link
http://secure.data-comm.com/DC/Detail.bok?no=7213

 

Yeah its the correct stuff... should be able to find it in the gear oil section of any suto part chain store.. back by the grease guns

 

For Austin Texas I would suggest SAE 85W-140 due to your typical temperatures. For cooler areas SAE 75W-90 would be fine. Lucas or Redline preferred but generic parts store brand is OK unless it is a dedicated track car.
Whatever you use you will also need a friction modifier due to the limited slip differential on the SE. Sta-Lube Equa-Torque Limited Slip Additive (by CRC) is available at most chain auto parts stores.

 

yeah but going through the manual, it says just to use SAE 90 and not any kind of XXW-XX oil. or is that just a suggestion by mazda?

 

Redline and Amsoil LSD lube should be easily available in any metro area.

 

order some royal purple 75 90 from racing beat. ive had no trouble out of it in all my cars.

 

The ##W is part of the SAE grade. 75W-90 is SAE 90. The 75 means it's effective above 75 degrees (I'm pretty sure). Royal Purple is good stuff, you can find it at any O'Reilly's store in Austin, it'll be behind counter.

 

UNDERSTANDING VISCOSITY
"Viscosity" refers to how easily oil pours at a specified temperature. Thinner oils have a water-like consistency and pour more easily at low temperatures than heavier, thicker oils that have a more honey-like consistency. Thin is good for easier cold weather starting and reducing friction, while thick is better for maintaining film strength and oil pressure at high temperatures and loads.
The viscosity rating of a motor oil is determined in a laboratory by a Society of Automotive Engineers (SAE) test procedure. The viscosity of the oil is measured and given a number, which some people also refer to as the "weight" (thickness) of the oil. The lower the viscosity rating or weight, the thinner the oil. The higher the viscosity rating, the thicker the oil. Viscosity ratings for commonly used motor oils typically range from 0 up to 50. A "W" after the number stands for "Winter" grade oil, and represents the oil's viscosity at zero degrees F. Low viscosity motor oils that pour easily at low temperatures typically have a "5W" or "10W" rating. There are also 15W and 20W grade motor oils. Higher viscosity motor oils that are thicker and better suited for high temperature operation typically have an SAE 30, 40 or even 50 grade rating. These numbers, by the way, are for "single" or "straight" weight oils. Such oils are rarely used in late model automotive engines but may be required for use in some vintage and antique engines.

MULTI-VISCOSITY OILS
Most modern motor oils are formulated from various base stocks so the oil will have the best characteristics of both thick and thin viscosity oils. Multi-viscosity oils flow well at low temperature for easier starting yet retain enough thickness and film strength at high temperature to provide adequate lubrication. A thin oil such as a straight 10W or even a 20W oil designed for cold weather use would probably not provide adequate lubrication for hot weather, high speed driving. Likewise, a thicker high temperature oil such as SAE 30 or 40 would probably become so stiff at sub-zero temperatures the engine might not crank fast enough to start. Multi-viscosity grade oils have a wide viscosity range which is indicated by a two-number rating. Popular multi-viscosity grades today include 5W-20, 5W-30, 10W-30, 10W-40 and 20W-50. The first number with the "W" refers to the oil's cold temperature viscosity, while the second number refers to its high temperature viscosity.

 

thanks wecycle. i get it now. so i would just want to avoid anything with friction modifiers since it's essentially a wet clutch like a motorcycle for a gslse LSD right?

 

When I installed my SE rear end a few months ago, I used the Royal Purple lube (found it at Pep Boys auto parts). I had some chatter with it, so I added a modifier a few weeks later and that took care of it.

 

"Multi-viscosity grade oils have a wide viscosity range which is indicated by a two-number rating. Popular multi-viscosity grades today include 5W-20, 5W-30, 10W-30, 10W-40 and 20W-50. The first number with the "W" refers to the oil's cold temperature viscosity, while the second number refers to its high temperature viscosity."

Wecycle essentially has it right, but I think the term "multiviscosity" is misleading. All lubricating oils have "multiviscosity". The viscosity varies with temperature. What are commonly called "multigrade" oils are oils that have had their molecular structure modified so that the viscosity VARIES LESS with temperature. The attached curve has the kinematic viscosity on a logarithmic scale, so the the curve versus temperature is virtually a straight line. You can see in the example that SAE 10 and SAE 40 curves have about the same slope, whereas the 10w-40 has a flatter curve. This simply means the oil retains more of its viscosity as it heats up. The standard measurement points are 0 degrees F and 210 degrees F. So the 10w-40 has the viscosity of a 10 weight mineral oil at 0 degrees F and the viscosity of a 40 weight mineral oil at 210 degrees F.

If they want to spend enough money, it is possible to get some very impressive numbers. I can recall seeing 10w-50 for sale.