[citizen_insane]

I'm looking to change out the transmission fluid on my 6-spd E90 328i. I've seen 3 main suggestions: Redline ATF D6 (not D4, I live in Iowa, it gets cold), Redline MTL and OEM Bmw MTF.

I've heard people saying they prefer both the Redline products over OEM, but there doesn't seem to be much of a consensus. I've read NOT to use Royal Purple since the OEM fluid left in the tranny/diff will degrade it after a few months.

ECS tuning recommends the Redline MTL and I'm somewhat inclined to listen to them since I assume they know what they're doing (they've been in business for quite a while).

I'm also planning on using Redline 75w90 for my diff. It matches the spec for the OEM non-LSD fluid from what I've seen.

Anyone want to chime in on what to use?

[Surly73]

Originally Posted by citizen_insane

I'm looking to change out the transmission fluid on my 6-spd E90 328i. I've seen 3 main suggestions: Redline ATF D6 (not D4, I live in Iowa, it gets cold), Redline MTL and OEM Bmw MTF.

I've heard people saying they prefer both the Redline products over OEM, but there doesn't seem to be much of a consensus. I've read NOT to use Royal Purple since the OEM fluid left in the tranny/diff will degrade it after a few months.

ECS tuning recommends the Redline MTL and I'm somewhat inclined to listen to them since I assume they know what they're doing (they've been in business for quite a while).

I'm also planning on using Redline 75w90 for my diff. It matches the spec for the OEM non-LSD fluid from what I've seen.

Anyone want to chime in on what to use?

If you're rejecting D4ATF because you feel it's too thick for your climate, MTL will be even worse as it's thicker. Now, I've used 9cSt fluids like Redline MTL and Amsoil MTF in my E39 in a (southern) Canadian winter with no problems whatsoever so....

Your Amsoil equivalents would be Amsoil MTF and Amsoil 75W90 (SVG) for the rear end. I've used both Amsoil and Redline in BMW drivelines and I've been happy. My E90 has Amsoil in it right now.

[citizen_insane]

Originally Posted by Surly73

If you're rejecting D4ATF because you feel it's too thick for your climate, MTL will be even worse as it's thicker. Now, I've used 9cSt fluids like Redline MTL and Amsoil MTF in my E39 in a (southern) Canadian winter with no problems whatsoever so....

Your Amsoil equivalents would be Amsoil MTF and Amsoil 75W90 (SVG) for the rear end. I've used both Amsoil and Redline in BMW drivelines and I've been happy. My E90 has Amsoil in it right now.

I did not realize that thanks. I've just heard people say that D6 is better than D4 for colder climates, but there isn't a whole lot of info out there. I guess I don't know much about how the thickness of the lubricant will effect the longevity of the transmission.

[Surly73]

Originally Posted by citizen_insane

I did not realize that thanks. I've just heard people say that D6 is better than D4 for colder climates, but there isn't a whole lot of info out there. I guess I don't know much about how the thickness of the lubricant will effect the longevity of the transmission.

If I remember correctly, MTF-LT1 was around 9 cSt. I've seen conflicting information about whether MTF-LT2 was ~7 cSt or ~9 cSt. MTF-LT3 is definitely a lower viscosity fluid <7 cSt.

BMW's trend is thinner, just like all car manufacturers obsessed with meeting CAFE requirements. Aftermarket fluid suppliers like Redline recommend fluids on the thinner side so they're sure that people don't complain about poor shifting with their fluids.

That being said - thinner MIGHT shift better, as long as it's still within operating range for the transmission. There are lots of other car brands out there where people complain about shifting getting worse when hot - it's too thin.

Generalizing, slightly thicker fluids will do a better job protecting bearings and the gears themselves. One might say that it's best to use a fluid "as thick as possible" which still preserves acceptable shift quality in your normal temperature range.

Furthermore, friction modifiers are added to transmission fluids which dramatically affect shift quality and how the synchros behave. Synchros need to be "grippy" and without added friction modifiers, gear/engine oils are not "grippy" and shift quality will suffer.

I prefer to select a fluid which is designed from the get-go as a manual transmission fluid, not an ATF which happens to work OK. This is why I usually stick with Redline MTL or Amsoil MTF - designed for MTs from the start. ATF does have friction modifiers too, but the design parameters don't necessarily match MTs.

The thinner fluids in the 7 cSt range are in the same range as ATF. D6 ATF is thinner than D4 ATF (because the Dexron VI spec is thinner) and may be a better match for MTF-LT3 (if that's important to you). I care more about longevity and shift quality than precisely matching a particular target viscosity.

Both RL MTL and Amsoil MTF are ~9cSt fluids which are a little thicker (better bearing and gear protection) and match the characteristics of MTF-LT1 reasonably closely.

Redline MT90 is substantially thicker and matches a 75W90 gear oil in terms of viscosity. I know people in warmer climates running MT90 in BMWs with great results too but the average Joe may run into issues. If you DIY, it's about $15 a pop to try all the gear oils you want. If you don't DIY it's far more annoying and costly to play around.

As with most of the fluids in the car - it's more important to change it regularly than to obsess about exactly which fluid you're using.

[citizen_insane]

Thanks for taking the time to further explain it, looks like I won't sweat it as much and I'll probably end up going with the Redline MTL. I'll post again to report how it works after I change the fluid.

[Tom K.]

Originally Posted by Surly73

I prefer to select a fluid which is designed from the get-go as a manual transmission fluid, not an ATF which happens to work OK. This is why I usually stick with Redline MTL or Amsoil MTF - designed for MTs from the start. ATF does have friction modifiers too, but the design parameters don't necessarily match MTs.

I appreciate your reasoning and will be deciding on a fluid next year for my E91 and 128i. MTL worked very well on my E46 5 speed, but why do you think Red Line recommends D6 for the E90, rather than MTL?

Tom

[Surly73]

Originally Posted by Tom K.

I appreciate your reasoning and will be deciding on a fluid next year for my E91 and 128i. MTL worked very well on my E46 5 speed, but why do you think Red Line recommends D6 for the E90, rather than MTL?

Tom

My E90 came with MTF-LT2 according to the sticker on the transmission. I know that later ones seemed to come with MTF-LT3 from the factory.

MTF-LT3 is thin, and D6 ATF is the closest match in that regard. Notice that the transmission didn't change when the sticker changed - it's still the same as when the E90 was launched.

I spoke/emailed with Dave @ Redline once about MT fluid recommendations and he basically told me that they spec ATF because it's the thinnest and they don't want any BMW owners from Alaska complaining (possibly publicly) that Redline caused hard shifting. He told me that MTL and MT90 would also be perfectly fine to use in my E39 but that I *might* have some shift feel degradation depending on how cold it gets where I am.

So, all that being said, I like MT-dedicated fluids the best and have run MTL through Toronto winters for years with no problems whatsoever. Ditto for Amsoil MTF.