Changed rear diff and transfer case oil to Redline 75w90. I know Mazda says 80W90, but that's for crap oil with a narrow viscosity index and also leads to increased resistance to flow at cold temps, resulting in increased wear. The Redline being composed of only PAO base stocks has greater stability under hot temps, high shear loads, etc and protects and flows better at cold temps down to -50F and has a much better viscosity index across a much broader temp range and will last for the life of the vehicle, pretty much with the wife driving. Glad I did it to the wife's car because Mazda vastly underfills both units. They should both take about 0.48 qts, at which point the oil should be to the level of the fill plug on even ground. Removed both fill plugs and nothing came out of either! Measured the transfer case oil drained out and it was only about a 1/4 quart. Same for rear diff. The rear diff is a bit of a PITA, because the cross member is so close to the fill plug, you can't use a torque wrench. Replaced all four washers (they're all the same) and torqued 3 of the 4 to 35 ft*lbs, mid range in the Mazda spec. They also use a 23mm for the fill plugs and a 24mm for the drain plugs, go figure. Not much metal on the magnetic drain plugs, but the oil was definitely starting to degrade from the heat, as it was starting to dark brown to black. Only wish my CX-9 had a drain plug on the xfer case, it is a major PITA to get access to and suck out and refill. Given the hot environment the xfer case lives in and the ridiculously small oil volume of both the diff and xfer case, I feel much better now. I took it out for a pretty extreme test drive in 90+F weather and after a few miles the vehicle seemed much smoother under both partial and full throttle, not that it was bad before, but it definitely made a difference. Even the butt dyno said "yeah baby". Probably see a couple mpg's increase too. 29.3 mpg avg in combined now.
Haven't posted in a long time, so I don't know if my sig has my vehicles in it & I didn't check, so...
1994 Mazda FD3S - Owned new since Dec 1993. 24,700 miles. Lots of goodies.
1995 Eclipse GSX - Owned new since Oct 1994. 32,400 miles. Lots of goodies, too!
2005 WRX STi - Owned new since Nov 2005. 34,100 miles. A few goodies from my 94 that got totaled. Lots of stuff left to put on some day.
2012 Mazda CX9 GT AWD - Crystal Pearl White/Beige Leather Interior - Owned new since Mar 2012. 15,600 miles. Full front, hood, fenders & mirrors clear bra installed by the same guy that does the C7-R's.
Full WeatherTech liners 1st, 2nd,3rd rows and rear cargo. Mazda remote start. Upgraded rotors,pads and fluid. Latest Nav CD. Upgraded high performance all season Yokohama tires. Mazda splash guards.
2015 Mazda CX5 GT AWD - Liquid Silver Metallic/Black Leather Interior. Bought new July 2014. 25,600 miles. Wife's car. Long commute. Full WeatherTech liners 1st, 2nd rows and rear cargo. Mazda hood protector. Mazda SS bumper protector. Mazda remote start. Mazda splash guards. Latest Nav updates/fixes.
Other Mazda's: 1980 RX7 (my first car, learned about trailing throttle oversteer real quick!), 2000 Mazda Millenia S Millenium Edition, 2008 Mazda CX-7