Whats the best gear oil and diff oil you can use on an 2010 RX8 GT 6spd manual? Is using synthetic ok?

 

Some very good information on this here.

Manual Transmission: Motorcraft XT-M5-QS
This stuff is magical. I use it in the S2 gearbox in my S1 and it's awesome.

Differential: Any 75w90 GL5 will do. Opinions on the best will differ significantly.

 

I changed both Trans and Diff to Redline and it worked great. Transmission feels a lot less crunchy when cold and hot.

 

I've seen some significant hype around that M/T oil. Is that stuff GL-4/okay to use in an S1 transmission?

 

Just use OEM fluid, there is no reason at all to use anything else.

 

It depends on your goals.

OE fluid is fine.

The referenced Motorcraft fluids are well-liked in Miatas and RX-8s.

If you are tracking the car, Redline MT-90 in the trans and 75W90 in the diff is a popular combination.

If you are wealthy, Amsoil makes wonderful gear oils.

 

I've seen quite a significant amount of good things about this as well, my only hesitation was that it's apparently a GL5 oil, and as far as I know GL4 is what most folks recommend in the S1 transmission.

 

So your customers use it in both the m/t and the differential? How does it compare to just using redline for example? I'll check out the results on your site as well. Thanks for the information.

 

Sounds good. I like the idea of only having to order one fluid for both the transmission and differential. Maybe I'll change my fluids early and try this next summer.

 

Im trying to get one that has a long service life but wont compromise protection and performance...heck If I can get one that's like on newer cars where the Tranny is pretty much sealed and don't have to worry about fluid change until you replace clutch that would be great.

 

I hate to resurrect a dead thread just to say this, but the results were so good I had to let you know, Charles.

I noticed that when I changed my differential and trans fluid I was missing a crush washer for the fill plug on the trans. I tried not to worry too much about it, but my cautious side got the best of me and with the semester being over I decided to change my fluids again and replaced the crush washers and bolts with OEM mazda parts that I got when I went to have my warranties serviced.

The eneos stuff is unreal. The shifting wasn't bad before, but with this new gear oil I go into reverse at least 100 times better, and shifting is just silky smooth with minimal force. I couldn't be happier. Appreciate the wisdom, my friend.

 

9K - what is the OEM fluid. 3 Mazda dealers told me they use whatever is in bulk - all 3 had Mobil GL-5 75W90 in 55 gal - the wrong fluid. They didn't have a part number for unit containers either.

 

Some feedback on the Eneos...

I put it in my trans a few days before a track day and on the street I experienced all the buttery shifty goodness that's described in this thread. However, when I got on the track and things got a little warm (engine coolant temps around 210 F), the shifts got difficult. I had to be patient and double-clutch every downshift as if I had no synchros. This wasn't an issue before with fresh Neo Synthetic gear oil (my previous two trans fills). Thoughts?

 

The Motorcraft XT-M5-QS in my S2 gearbox is a little notchy on cold winter mornings (<32°F) but works fine after a few miles driving all the way up to the end of a 20-minute session on the track.

 

Thanks for the reply guys...Ive been reading about AmsOil Synthetic and its seems pretty good reviews and it actually can go past 500,000 miles without changing it...not that i wont change my Tranny and Diff Oil but its nice to see that the oil dont breakdown much.

I guess thats why newer cars have the tranny sealed cause gear oil made it a long way...

 

Swepco SW210 is what save my tranxale desert racing, everything else has me rebuilding earlier

 

Sorry to revive a dead thread, but I have to ask, does amsoil still make oe fluids? I drive my rx8 on namely street and make a couple donuts every once in a while but never enough to consider it track worthy. Specific suggestions for me? Aiming for smoother transitions between each shift.

 

I just put Amsoil in my tans and diff about a month ago. The trans feels noticeably better shifting. The ideal shift feel minus possibly a slightly worn shift bushing which I haven't dug into yet, but wouldn't have noticed were it not for the fluid. I live about 2/3 up a windy canyon road, and on the original fluid, the diff would be noticeably hot when I pulled into the garage (I could smell the hot metal). I checked the fluid level, and it was full. Haven't had that happen since the Amsoil went in.

 

I used Redline and Motorcraft in my first 8. This one is on its first fill of Amsoil and while it shifted well new it wore out after 3 track days now not shifting that great anymore. I found with my last one Redline lasted the longest so that’s my recommendation.

 

I'm going to conditionally retract my Amsoil endorsement... I've been having issues with the synchro on 6th gear below 60mph... Very weird. I just ordered a couple of quarts of the MT-90, and if that solves the problem then it was the Amsoil. It's been a while since I parked in the barn after a hard run up the canyon, but it might still get at little hot when pushed hard. One thing at a time...

 

I highly recommend the RedLine products in my 2010 Series 2 (Series II). About 18000 mi since the change in fluids in my MT and rear differential and no issues with shifting, noise, etc.

 

If the Redline cleans up the 6th gear issue, I'll just go ahead and switch over the diff as well. I've used Amsoil for a long time on a lot of vehicles and never had issues. This one is just too weird though. Synchro issues are almost always on 1st or 2nd gear, definitely not top a top gear thing... Then, it only occurs at LOWER speeds. Like if I shift into 6th from any gear below 60 or so, the synchro can't seem to spin up the input shaft enough to not crunch a little. I can't even fathom how that would happen at all in the first place... Sorta same deal with the diff getting hot enough to smell. It's a friction based TorSen, and I'm throwing it hard through a lot of tight bends, but even then... Never had a diff get that hot. The Amsoil certainly cooled it down some, but I'd still prefer the diff to continue to be the sort of thing I only think about at major service intervals, and only for a fluid change.

 

Any luck with this? Going through almost the exact symptoms and planning on doing a trans/diff fluid change as well.

 

Shipped yesterday. I've got major unplanned home repairs going on, and a baby due in... 25 days... So it may be a few weeks before I have the time to flush my trans and get some miles under it. I'll try to remember to keep you posted though.