Best fluid for BMW 6 speed Manual?

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TheRuss

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Hi folks,

I have a 2009 BMW 135i manual 6 speed and want to change out the rubbish "lifetime fill" in the transmission and diff.

However, I'm getting conflicting information from all over the place, so am utterly confused.

A lot of the advice I read is to use Redline products (probably because they're highly revered in the BMW world), however nobody seems to agree on exactly which product to use.

I believe that my trans comes with an ATF as standard, and Redline themselves recommend their D6 ATF, as it most closely matches the BMW specs.
However, my oil dealer recommended I use the Redline MTL fluid, which is thicker, and as I understand, lubricates better. I mentioned that cold weather shifting was pretty important to me, and was then recommended to mix Redline D4 ATF with the MTL for the best of both worlds.

I've also seen elsewhere that running just MTL is apparently what gearbox builders have been recommending and what they've been filling the gearboxes with after rebuilding.

There seem to be anecdotal accounts of MTL, D4, and D6 all being used, but I just really want to know which is best. I read an article by Mike Miller (supposedly a BMW guru of sorts?) stating that ATFs aren't really very good at lubricating bearings. He said that he'd always use MTL unless he couldn't trust the driver to shift proerply in cold weather, in which case he'd use the D4.

My car currently has approx 38,000 miles on the clock and shifts OK, though could be better betwen 1st-2nd and sometimes requires me to lift and re-depress the clutch to get into first, although this only happens occasionally. I understand that some have experienced this from new on more BMWs, so I think it's just a gearbox trait.

I'm also in the UK where it can get to around -10 centigrade in winter sometimes, but mostly sits around 0 - 5 degrees through winter and winters seem to be lasting longer and longer these days! Today it's supposed to get up to 20 degrees though (still centigrade) so it's not the coldest place around - probably similar temps to New York, I suppose.

My daily journeys see the car warming up just by the end of the journey (about 15 miles each way) so it spends most of its time cold or cold-ish, however, I don't want to just plump for an ATF for the cold shifting qualities if it doesn't have great lubrication for the bearings, so based on the above, what would be the best fluid for my car's transmission? Or what would you recommend?

Thanks in advance for any help you can offer.

Russ
 
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With the conflicting information, I would call Red Line and ask them. Bavauto.com is a RL dealer and the only do BMW and Mini so they would be a great reference.

Personally, I would use D4 or D6 because I had a manual that spec'd ATF and worked great. RL D4 is GL-4.
 
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So Amsoil say to use BMW's own oil? Or just one similar to that spec?
 
Yeah, I read that yesterday amongst all my other hours of research that lead to nowhere!

There's plenty of anecdotal evidence for all three fluids, sure. But I just want to know which one is likely to be "best" for my tranmission and keep it happiest. My car is modified already and will soon be modified further, putting more power and torque through the drivetrain than stock, so I want to keep it as happy as possible with the right fluid, rather than leaving the lifetime fill junk in there.

My oil supplier is suggesting a mix of either D4 or D6 with the MTL. I've also read anecdotal reports of folks living in southern Canada and happily running the MTL. The Redline link you posted even said that Mike Miller and others heartily recommend the MTL as well, even though Redline themselves stick as close as possible to the factory fill. They don't really explain why they stick close to the factory fill though, but my guess is that they want to avoid any litigation that might arise from suggesting something not particularly similar to the standard fill and then having a customer's gearbox blow up.

When it comes to the ATFs though, are they really not great lubricants for the bearings, as Mike Miller suggests? If it wasn't for that comment and saying that MTL protects the gears better as well, I'd probably have just gone with the D6 and (I guess) enjoyed the smoother cold shifting properties. Instead I'm wondering if MTL or a mix of the two is a better option that will keep my transmission happier?
 
Originally Posted By: TheRuss
A lot of the advice I read is to use Redline products (probably because they're highly revered in the BMW world), however nobody seems to agree on exactly which product to use.

Same thing happened to me when I got my car. Everyone said to use Red Line D4 ATF in the transmission and Red Line 75w-90 in the differential, so that's what I did.

I now use Motul fluids. Motul Multi-ATF shifts at least as well as Red Line D4 did, and its shift quality never seems to degrade (which is vastly more than I can say of Red Line D4).

Of the fluids I've tried, though, Red Line seems to be the best of the rest.


Originally Posted By: TheRuss
I believe that my trans comes with an ATF as standard, and Redline themselves recommend their D6 ATF, as it most closely matches the BMW specs.
However, my oil dealer recommended I use the Redline MTL fluid, which is thicker, and as I understand, lubricates better. I mentioned that cold weather shifting was pretty important to me, and was then recommended to mix Redline D4 ATF with the MTL for the best of both worlds.

I've also seen elsewhere that running just MTL is apparently what gearbox builders have been recommending and what they've been filling the gearboxes with after rebuilding.

I've heard similar.

On the flip side, the fact remains that ATF is what BMW have specced. As far as I know, BMW has specced specialty fluids for its transmissions in the past, so they are not incapable of it when it is warranted.


Originally Posted By: TheRuss
There seem to be anecdotal accounts of MTL, D4, and D6 all being used, but I just really want to know which is best. I read an article by Mike Miller (supposedly a BMW guru of sorts?) stating that ATFs aren't really very good at lubricating bearings. He said that he'd always use MTL unless he couldn't trust the driver to shift proerply in cold weather, in which case he'd use the D4.

Anecdotes are all you'll get. No one has done the necessary work to verify these claims.

As for Mike Miller, I'm pretty sure I know the article you're talking about, and it's full of fallacies. I wouldn't put much stock in it. At a bare minimum, "I can't trust the driver to shift properly in cold weather" sounds an awful lot like "I can't trust them not to complain about very bad cold shift quality." What is "proper" cold shifting anyway? Surely he's not suggesting to double-clutch and rev match every single shift until the transmission is warm, let alone that this should be an acceptable compromise in any remotely modern non-cheap car...
 
Not sure how much replacement fluid is from the dealer - if they even would have any. The tranmissions are a "lifetime fill" afterall, so why would they have any to sell to anybody?

My oil supplier is saying that a mix of the D6 and MTL would be a good idea, retaining the superior shifting qualities of the D6 with the added protection of the MTL.

Does that sound feasible?

With regards to BMW's specs for the transmission, it seems that BMW care less about the transmission's health and more about mpg and pollution targets. The thinner fluid, the less transmission losses, I guess. Whilst that's certainly a concern of mine as well (who likes using more fuel and getting less power to the wheels?!) I wouldn't want to opt for the fluid that improved those variables whilst sacrificing the transmission in terms of wear and tear.
 
Originally Posted By: TheRuss
Not sure how much replacement fluid is from the dealer - if they even would have any. The tranmissions are a "lifetime fill" afterall, so why would they have any to sell to anybody?


There are indeed stories of dealers not selling trans fluid to customers for that reason..."sir, it's lifetime, you don't need this and we don't want to be liable for any problems you might cause."
 
The other reason is that for those who have been able to get it have found it to be ridiculously expensive (most likely just because it has a BMW badge on it), but is very thin and doesn't improve shifting when you change it.
 
Pentosin MTF2 is the proper fill for your car. It doesn't get much better than this fluid. It is the OEM fluid for less cost.

Redline MTL, even though it is a 70W-80, it about 60% THICKER than what your transmission came with. I would only run that in your car if you were going to drive it really hard.
 
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Well my oil supplier is suggesting mixing D6 and MTL together and running that. I guess that'd thin it out and give me the extra lubrication of the MTL as well?

So the Pentosin stuff is good? I'll go Google it.

I'm at the point where I'd happily pay double for a fluid if it was guaranteed to be the absolute best for my car, but as usual with auto fluids, there is no "best" it's all just opinion and guesswork.
 
Did I give my 2c to this on the thread at 1addicts?

Ive not been satisfied with redline shift feel longevity in my BMW gearboxes. Ive had much better luck with Amsoil.

That said, if youre stuck with an ATF (Ive not tested an MTL type viscosity in my 135 gearbox), the D4 may be acceptable. Ive seen recommendations from GM themselves not to use Dexron VI in MTs.

Id also look at G4 rated ATFs from Amsoil and others.

But the reality is that the Pentosin and BMW products may have similar cost and performance structure, and likely arent bad fluids. The lifetime concept may not be the best, but if youre changing the fluid, then Im not sure there is a big deal.
 
I just ordered the Pentosin MTF2 for my M5 from Turner because I couldn't get a straight answer (and the testimonials/issues people have had with other fluids can be scary) on acceptable alternatives to the OEM-spec fluid.

IMHO, I'd do as JHZR2 appears to be advising and order the Pentosin product.
 
Same in the Mustang community. I've got a 2010 GT. it comes with ATF and Red Line recommends D4, but people on the Mustang sites swear by Red Line MTL. They also speak well of Amsoil products. One guy called Tremec, who made the manuals prior to 2011. He got a recommendation for Mobil 1 ATF.
 
Originally Posted By: TheRuss
Not sure how much replacement fluid is from the dealer - if they even would have any. The tranmissions are a "lifetime fill" afterall, so why would they have any to sell to anybody?



They obviously will be able to order it. There are services where replacing the transmission fluid will be required, or at least topping it off. Think a seal replacement or something similar.

I'm simply asking because you started a thread where you're considering a home-brew, when you could just order the correct fluid from BMW.

It's your car, so do as you please. But I personally got tired of trying different fluids in my Nissan. After Amsoil and Royal Purple were worse than the OE fluid, I just went with dealer fluid. All three of our cars have genuine dealer fluid in the trannies. Sometimes dealers won't have it and will have to order it, even when it's not a lifetime fluid.
 
Originally Posted By: Old Mustang Guy
Same in the Mustang community. I've got a 2010 GT. it comes with ATF and Red Line recommends D4, but people on the Mustang sites swear by Red Line MTL. They also speak well of Amsoil products. One guy called Tremec, who made the manuals prior to 2011. He got a recommendation for Mobil 1 ATF.


Some gearboxes can take it no issue. For example, the gearbox in my E30 318i is specced for Dex II. I used MTF in it for years. Always felt good at the start, but lost feel fast. Went to Amsoil MTF, which is also a 5w-30 type viscosity, and it feels great nearly forever. Still, the box was specced for ATF. It works in the coldest winter. Some boxes get stiff even in the summer, at the start, if you deviate...
 
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