Choosing a Gear Oil

[Scott P]

I plan on changing out the fluids in my recently purchased MazdaSpeed 6. I am going to use Red Line MT-90 in the transmission. For the rest of the driveline, I'm not so sure. The manual calls for 80W-90 GL-5 for the transfer case and rear differential.

Is there a major difference between the various synthetic gear oils? I know of Redline, Amsoil and Royal Purple. Is one better than the other? The car is a daily driver and doesn't get raced . I just want to upgrade the fluids int he car.

 

[mechtech2]

It seems that individual cars like certain lubes. They simply shift better with one over another, sometimes.
Redline is OK, but dated. Amsoil sounds VERY good, but I haven't tried it yet. I've heard iffy reports about the RP.

 

[unDummy]

I've never found MT90 outdated. Redline fluids work excellently. Amsoil also makes a GL4 MTG for manuals.

If buying online, pick one brand and use their products everywhere. Grab some 75w90 for the x-case/'end and practice a sensible change interval, 30k or less. Since this vehicle has a bunch of HP, I'd consider 20k intervals.

IMO, there isn't much of a difference between the brands. Neo, Motul, Redline, Amsoil, Royalpurple, Synlube........ all make excellent fluids. I do find that some transmissions do better with one over the other. But, this tends to be vehicle specific. 2 identical cars might shift better with different fluids.

Since this is simply a daily driver, flip a coin and don't worry about it. If shifting becomes worse or annoying, pick a different brand at your next maintenance interval.

I also find that the 2nd fill of a fluid usually works better then the initial fill. Too many here abandon or slam a fluid without giving it a good rinse and long enough run.

 

[Scott P]

Thanks for the tips. I guess I'll just price shop and see what I come up with. Royal Purple is based in my little town, maybe I'll support the local economy.

 

[wileyE]

If you know what's in there now, and notice it shifts better colder than hotter, you next oil selection might be one with a slightly higher cst. Or visas versa, if it now shifts better when good and hot you next pick may want to choose thinner. So much of it is personal preference on shift feel, some like buttery smooth feel, some prefer the snick-snick feeling.

 

[aquariuscsm]

I`ve noticed my manual tranny shifts much smoother when it`s cold (on first drives of the day),then gets notchy once it`s hot. I`m sure it`s the synchro issues,but I`ve considered a heavy gear oil (85W140) to maybe smooth it out till I install my new tranny.

 

[CBDFrontier06]

There has been a recurring issue on some of the Mazda6 boards citing a rear differential 'whine' at 40-50mph and those who have replaced the rear diff fluid with synthetics are now advising against it. While it protects the diff fine, it in some cases caused the whine to become louder. They guys on the boards who are changing their own fluids are highly recommending sticking with a dino oil for the rear diff. I changed mine over to Lucas 80W-90 and the whine has been greatly silenced.

Changed my transmission over to Redline MT-90 and haven't had any further protest from 2nd gear, so that seemed to work well.

Haven't changed out the transfer case fluid yet...the jury is still out on what I plan to use there.

Good luck!

 

[Scott P]

My MS6 is a late build, May 06, so it seems to have escaped the few issues with the other cars.

 

[pp_rp]

Support your local economy. Use Royal Purple Max Gear. It's what I use and Like.

 

[unDummy]

Synthetics don't cause diff whine.
I know Mazda well enough and can say that 'undersized' price cutted components is an issue.
If the rearend has issues, make sure oil level is perfect. If it still 'whines', use a thicker gear oil, add a shot of LSD additive, simply exercise the warranty, or any combination that works for you.

Since RoyalPurple is local to you, and your location is Houston, I would definitely consider their 75w90 for the manual, and either the 80w90 or SAE90 for the rearend.

If it were mine, I'd use the 75w140 in the rear. Or, minimally a 50:50 blend of the 90wt and 140wt gear oils.