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21 Posts
Discussion Starter #1
On my Acura I ran GM syncromesh FM. Very smooth shifting. Looking for similar shift feel on the m3. Not going to track the car, just spirited DD. I don't abuse my syncros, double clutch, and live in a temperate climate.

What MT oil does everyone recommend on the m3 for smooth shifting?

Motorcraft XT-M5-QS "Honey" (75w90) has a following and only a few issues mainly with track cars. It's just barely a 75w90 so better shift feel vs. most 75w90s.

Redline MTF (75w80) seems like the default pick now for under warranty cars, esp. since Mazda derated from 75w90 to 75w80 a few years back. Does Redline 75w80 have smoother shifting vs. Motorcraft?

Amsoil MTF (75w80) and MTG (75w90) are popular on the Miata boards and other Mazda 3 boards. Amsoil MTF has slightly lower viscosity vs. Redline 75w80 and others have said it's much smoother shifting. Anybody running Amsoil MTF on the m3?

21 Posts
Discussion Starter #2
background info

From miata.net
oldboy said:
I have tried the two holy grail GL-4 fluids (Redline & Ford). I never had that great shifting that everyone was talking about. So, I recently switched to Amsoil MTG GL-4 to give it a whorl. For me, the Amsoil, by far, the best of the three. I've had it in the car for a little over 2 months now and the shifting is much smoother and better than the other two. :thumbs:
From miata.net:
prb said:
I've had the 'wrong' Amsoil fluid in the transmission for a week now.


(This is MTF, the recommended Amsoil product would be MTG)

This transmission has never shifted this good. The 5W-30 Manual Synchromesh Transmission fluid has transformed the shifting. Rapid shifts between gears are just that. It goes right into gear even if you push it hard. No grind, no clunk, no anything but the snick of the next gear. It shifts perfectly when the transmission is cold. No more 2nd gear notchy behavior at any time.

I'm going to stop short of recommending because it's not the recommended lubricant grade for our manual transmissions. You make your own decisions if this is a risk you are willing to take.

The Viscosity Index of the Synchromesh MTF @ 100C is 9.7

The Viscosity Index @ 100C of a few 75W90 GL-4 lubes I have looked up are:

Redline 15.6
Pennsoil 15.3
Amsoil 14.8

So it's a considerably lighter oil than 75w90 GL-4.
From skyativ-mtf-choices:
I know MTF isn't specific to the skyactiv vehicles but since the transmission is, I thought it might be nice to have a thread of compatible MTFs and people's thoughts on what they have used in their skyactiv MTXs.

The OM specifies a 75W-80, GL-4 MTF. The GL-4 is what specifies the additive package protection requirements. This is probably the most important piece of the specification and I'd recommend avoiding any fluids that are dual rated for both GL-4 and GL-5 to be on the safe side (GL-5 fluids can harm soft synchro metals). The 75W-80 is a rather broad specification and many different types of fluid will work with this specification. The 100C viscosity for this spec can range from ~6 cSt all the way up to 10+ cSt. That is a fairly drastic difference in MTF viscosity to consider (67%+). Obviously the thinner fluids should have an advantage in severe cold starts and MPGs and thicker fluids could arguably provide more protection in extreme heat/hard usage at the cost of MPG.

Here are some common MTF GL-4 choices starting with the thinnest and moving to the thickest (40C cSt, 100C cSt):

1) Fuchs Sintofluid FE 75W (40.8, 6.7)
2) Royal Purple Synchromax (38.0, 7.7)
3) Pentosin MTF2 75W-80 (38.3, 7.7)
4) Pennzoil Synchromesh (41.6, 9.08)
5) Shell Spirax S6 75W-80 (56, 9.1)
6) Amsoil Synchromesh 5W-30 (48.3, 9.7) [Doesn't list GL-4 protection, but additive package apparently fits GL-4 protection levels]
7) Chevron Multigear 75W-80 (57, 9.6)
8) Redline MTL 75W-80 (54.1, 10.4)
10) Mazda OEM fluid (unknown)

Other fluids that could work well depending on your application are the dual clutch transmission (DCT) fluids. They usually run on the thin side but there are several that carry GL-4 protection ratings. I'm guessing the DCT fluids made for dry clutch applications would be the best best of the DCT fluids.

Other things to consider would be that a 75W-85 or 75W-90 GL-4 fluid would also work if preferred for some reason.
From mazdas242 best trans fluid used:
shpankey said:
I posted this on another forum, but figured I'd add it to this thread as it's a good thread with a lot of info...

I was a big believer in the Ford XT-M5-QS honey too, but eventually I had the 3rd gear synchros go bad while on it. When they tore it down the Ford fluid was near black and extremely thinned out. I had about the best person out there (Molakule at BitoG) recommend the GM Synthetic 12346190 fluid. His post...

"You might also want to try the GM Synthetic Manual Transmission Fluid, # 12346190. And it IS a real synthetic MT fluid with PAO's and esters and none of the pseudo-synthetic GroupIII oils.

It was specially designed for cold weather shifting."

...I asked it's kv 40 and 100 cSt stats...

"75 and 11.5 cSt, respectively."

...this is a GL-4 75w90 fully synthetic fluid btw, so it keeps you in warranty. Alternatively, Red Line has a new product out, MT-85, which lands in-between their MTL and MT-90 fluids... though it's not a 75w90 so it's not technically in warranty.

I have seen 3 of us now have synchros go out on the Ford Motorcraft XT-M5-QS honey, me being one of them, and after it sheared like that and came out so black I have no plans to put it in my brand new transmission. Sure, it does work miracles for shifting, I'm just not convinced it provides the long term extended protection I'm wanting. Molakule is probably THE most respected person on the internet about transmission and gear oils so when he recommends something, I definitely am listening. Those are some pretty high words from him about the GM Synthetic Manual Transmission Fluid, # 12346190 so I'm game. I love that lighter kv 100 cSt spec too (makes for easier shifting) and it's technically a true GL-4 75w90 fluid so that is important for getting the protection you need.

I won't lie, it's EXPENSIVE as heck at $22 a quart but for smooth easy shifting AND longterm quality protection, I'm IN. Being a true group IV and V synthetic is nice to know too. I don't like my gear oils having to use VII's.

Update to my above post, for reference so you can see this all side by side...

GM Synthetic MTF 12346190:
GL-4 75w90 ===== kv 40 cSt: 75, kv 100 cSt: 11.5, VI: , PP (c): , FP (c):

Red Line:
D4 ATF ======== kv 40 cSt: 34.0, kv 100 cSt: 7.5, VI: 198, PP (c): -60, FP (c): 225 (<- Automatic Transmission Fluid, you can see how thin it is)
GL-4 MTL 70w80 == kv 40 cSt: 56.2, kv 100 cSt: 10.6, VI: 183, PP (c): -50, FP (c): 232 (<- Basically a Synchromesh/max range of fluid)
GL-4 MT-85 75w85 = kv 40 cSt: 64.3, kv 100 cSt: 12.0, VI: 172, PP (c): -48, FP (c): 236 (<- Their new "in-between" stuff)
GL-4 MT-90 75w90 = kv 40 cSt: 90.0, kv 100 cSt: 15.6, VI: 185, PP (c): -45, FP (c): 240 (<- A "normal" ranged GL-4 75w90)
GL-5+ 75w90 NS == kv 40 cSt: 95.0, kv 100 cSt: 15.6, VI: 176, PP (c): -45, FP (c): 221 (<- A GL-5 fluid for transmissions)
GL-5 75w90 ===== kv 40 cSt: 115., kv 100 cSt: 16.4, VI: 155, PP (c): -45, FP (c): 227 (<- For differentials, you can see how much thicker it is)

Ford Motorcraft XT-M5-QS:
GL-4 75w90 ===== kv 40 cSt: 76.0, kv 100 cSt: 15.4, VI: 211, PP (c): -54, FP (c): 186

Amsoil MTG:
GL-4 75w90 ===== kv 40 cSt: 84.5, kv 100 cSt: 14.7, VI: 181, PP (c): -46, FP (c): 204
From bobistheoilguy Redline 75w80 in the mazda:
martinq said:
The Amsoil 75w80 MTF product is:

Synthetic Manual Synchromesh Transmission Fluid (MTF)

Very similar in spec to Redline MTL but with significantly better flow at -40C.
https://www.redlineoil.com/content/files/tech/Man Trans Lubes 10-13-1.pdf

From bobistheoilguy:
martinq said:
75w80 can be a 5w20, 0w30, 5w30.... Amsoil calls their MTF a 5w30 helps narrow down the visc range it falls into.

Redline's MTL is both... a 5w30 and 75w80.

GL3... not stressed enough to require GL4, but GL4 can be used.

Quit worrying. Just pick a fluid and use it.
I would stick with the 75w-80. Anything thicker for no real reason is just adding drag. If you said full on race car and beat the life out of it then perhaps something thicker. But for DD I say OEM weight.
From bobistheoilguy:

unDummy said:
With the move toward MPG, Mazda dropped the weight from 75w90 to 75w80 in 2010 for some of their manuals.

The real question, "is this the best weight, all else being equal?"

Was it for MPG? was it to reduce shift quality complaints and replacements?

Maybe they changed the gear material formula, or improved the gear heat-treat and decided to pay the supplier 'more' for the transmission wink2 ...... maybe they decided that an increase in wear is worth the risk for better MPG and statistically wouldn't affect warranty claims? maybe the easier/improved shift quality will make up for some of the warranty claims shrug ?

Give you a little hint from my days of manufacturing for certain automakers. Its all a give/take relationship with everything. If you get 1000 shift quality complaints within a given time interval, along with 25 failed gearboxes and are replacing all 1025 transmissions, imagine the number of "shift quality complaints" eliminated with a thinner fluid; maybe 500 limp-wristed shift quality complaints eliminated and 100 new failed gearboxes = 600 units replaced compared to 1025 the previous time interval! Cut 1 complaint issue in half even though we get 4x as many hard failures saves the automaker ~425 replacements. Hang out with some accountants and statisticians.

If you're happy with the possible misprint in your owners manual, then use the 80 weight GL4 gear oils. These are pretty much equivalent to any synchromesh fluid.

If you believe that maybe the automaker could care less if the transmission lasts more than a week after the warranty expires, or if you plan on keeping the vehicle long past its last payment, then maybe a 90 weight GL4 fluid should be used. Amsoil MTG and Redline MT90 are easy choices. Ford/Pennzoil/... also have options.

If you don't won't to wrestle the shifter with the 90 weight when cold, another option, is to step down to an 85 weight gear oil. Nissan/Kia/Hyundai/Mitsubishi.... have GL4 85 weight gear oil(75w85).
Or, do what we've being doing for years and blend your own weight by mixing Redline's MTL and MT90 in some ratio, or Amsoils MTF & MTG.
From bobistheoilguy Mixing Amsoil MTF and MTG:

MolaKule said:
Synchromesh is not a viscosity but a type of gear engagement system for manual transmissions.

The two fluids can be mixed to get the viscosity you need by experimentation.

They contain the same synchro friction modifier compounds and similar Anti-Wear additives; just different viscosities of base oils.

MTL or MTG can used in all kinds of synchromesh-type transmissions that use low or high viscosity fluids.

Historically, I think the reason the lighter fluids has been seen as the "synchromesh" fluid is that GM's original synchromesh fluid had a viscosity of about 9.5 cSt, so any MTL between about 9.0 cSt and 11 cSt is seen as a synchromesh fluid. And then of course, Pennzoil and Texaco picked up on it with a similar fluids.

*The Electrician*
905 Posts
that is alot to absorb lol, @arathol what do you think?

Super Moderator
5,977 Posts
I use Ford XT-M5-QS in my MX-5. It made a real difference despite what the few naysayers claim. It seems to work well in warm weather and cooler weather, don't drive it in the winter though so I don't know about that. From what I hear its pretty good all year though.
Redline isn't any good in colder weather it seems. The GM stuff is good for colder temperatures according to those who have used it.

Haven't done the fluid in the 3 yet so nothing there.

10 Posts
I just drained the factory fluid and re-filled with the Ford 75W-90 at 38,000 miles. Seems to be a little bit smoother but that might just be placebo effect or just from being clean fluid.

Overall haven't noticed an enormous difference.

44 Posts
I've replaced my transmission fluid with Redline, and I couldn't feel any difference. The shifts are already pretty smooth as is, it's hard to imagine them getting much smoother.
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