Best fluid for BMW 6 speed Manual?

[TheRuss]

Originally Posted By: stephen9666
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.


But what is the "correct" fluid? BMW change the fluid as and when it suits. Generally the manufacturers are moving to thinner and thinner fluids for better mpg and emissions figures. Doesn't mean it'll protect any good, just that it'll outlast the warranty.

 

[d00df00d]

I have to imagine that BMW knows it's not in their best long-term interest to sell cars that consistently disintegrate just after the warranty period expires.

If anything, I'd expect the "lifetime" fluid to last until about when the first transmission repair would be expected in most cases.

 

[JHZR2]

Originally Posted By: TheRuss


But what is the "correct" fluid? BMW change the fluid as and when it suits. Generally the manufacturers are moving to thinner and thinner fluids for better mpg and emissions figures. Doesn't mean it'll protect any good, just that it'll outlast the warranty.


Then again, an MT isnt that complex and there isnt a lot going on in there. While the fluids surely heat up, what's to say that the fluid wont last a good long time? If the shift feels ok and there isnt lots of metal in there, whats the big deal?

Then again, diffs use a fairly heavy lube, so it would be interesting to compare bearing and gear face surface areas and see how the lubes proportion to that.

 

[NorWest5]

I just today replaced the manual transmission fluid in my 2003 M5 which I've owned since new. BMW will tell you it's a lifetime synthetic and good to go for years. I reached 30,000 miles on the oddometer about 2 weeks ago and have owned the car since new. To me this was long enough in both time and mileage.

I did a lot of reseach on this to make sure that the fluid I chose was compatible and in the end I purchased 3 litres of Pentosin MTF-2 which is exactly the same synthetic fluid that BMW sells for this car. The transmission capacity on the E39 M5 is close to 2 litres but unless you use a fluid transfer device plan on spilling some. I also changed out my limited slip differential's fluid at the same time and went with the Castrol 75W-140 product made for BMW with the FM additive.

For the BMW LS differential be very careful about the fluid you choose to use or you will end up with clutch chatter very quickly.

 

[NorWest5]

Originally Posted By: TheRuss
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.


I would strongly recommend that you DO NOT do that. Use the fluid specified by BMW's engineers and made by Pentosin. See my other post on this.

 

[d00df00d]

Originally Posted By: NorWest5
For the BMW LS differential be very careful about the fluid you choose to use or you will end up with clutch chatter very quickly.

Small side note: I'm pretty sure all non-M cars have open diffs.

 

[MolaKule]

The BMW LT-3 fluids is one of those low viscosity 6.1 cSt MTL's.

The Castrol Syntrans FE 75W is an MTL of the same viscosity.

The next closest would be the Redline MTL 70W80.

I would avoid any ATFs unless that's the only choice I had because in my view, I have not seen any ATF's with a sufficient level of anti-wear additives for MTLs.

 

[mva]

My advice is to stick with the stock fluid or something with the same viscosity range.

After trying many fluids, I found that Royal Purple Synchromesh worked best in my BMW Z3 but that doesn't mean it will work best in your car. A thicker fluid can cause serious problems, such as the shift pin issues common to my car.

 

[Old Mustang Guy]

The Synchromesh fluids are considered to be a good alternative to ATF by the Mustang folk. GM specifies their Synchromesh for their 6sp manual Tremec equipped cars.

 

[TheRuss]

Originally Posted By: NorWest5
Originally Posted By: TheRuss
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.


I would strongly recommend that you DO NOT do that. Use the fluid specified by BMW's engineers and made by Pentosin. See my other post on this.


Why do you strongly recommend not doing that mix?

As for my diff - yeah, it's an open type with the "e-LSD" which just applies the brake to a spinning wheel. I'll likely use the Redline gear fluid for the diff in the correct grade.

It's just the transmission that I'm concerned about. One man's "that should work well" is another man's "I'd strongly recommend not doing that".

Basically, I'd like to not add any extra drag to the transmission where possible, I don't want poorer mpg or BHP at the wheels from parasitic transmission drag. However, I want a fluid that will lubricate and protect my transmission well, and the protection is more of a concern as I tune the car further and ask more of the transmission than was originally intended. Is there a fluid that fits this bill?

 

[dparm]

Originally Posted By: TheRuss

Why do you strongly recommend not doing that mix?



Those are two vastly different fluids that are not designed to be mixed. The additive packs are not the same and could potentially clash.

API motor oils must be mixable with other motor oils. I don't believe the same applies here.

 

[JHZR2]

Originally Posted By: d00df00d
Originally Posted By: NorWest5
For the BMW LS differential be very careful about the fluid you choose to use or you will end up with clutch chatter very quickly.

Small side note: I'm pretty sure all non-M cars have open diffs.


Maybe recent, but my 91 e30 318i has an LSD.

 

[d00df00d]

Yeah, there were a couple of non-M cars as late as the 90s that had LSDs, but nothing since then.

 

[TheRuss]

Yeah, the 135i has an open diff. It actually has what they call "e-diff", but it's just the car using the brake to stop a spinning wheel, so not anywhere near a proper LSD.

 

[NorWest5]

Originally Posted By: dparm
Originally Posted By: TheRuss

Why do you strongly recommend not doing that mix?



Those are two vastly different fluids that are not designed to be mixed. The additive packs are not the same and could potentially clash.

API motor oils must be mixable with other motor oils. I don't believe the same applies here.


Agree. Unless your replacement fluid meets the vehicles manufacture's specs: don't use that particular brand of transmission fluid. Mixing any replacement non-spec fluid while your vehicle is still under warranty will be Russian Roulette if there is an issue with your transmission before that warranty expires. Post warranty; do what you think best.

 

[JHZR2]

Originally Posted By: TheRuss
Yeah, the 135i has an open diff. It actually has what they call "e-diff", but it's just the car using the brake to stop a spinning wheel, so not anywhere near a proper LSD.


Anywhere near?

While its not mechanically actuated, is there really much a difference between a brake and rotor, vs a clutch and friction surface in an LSD, besides the fact that the brake may be more capable??

 

[TheRuss]

Yes. Yes there is. Else the e-LSD would be fitted to the M cars and race cars. You'll put power down much better with a proper LSD.

 

[JHZR2]

Ok but I'm seriously asking - what's the difference in dynamics that makes the one better? Sure people demand the old standard, which surely has much to do with it.

But a rotor with a bake pad clamped down sure can stop a wheel and hold a vehicle well. And there is more friction surface, I'll bet.

I know when we were in a lot of snow in friends' CRV, it stunk bad from the use of brakes as an LSD. But I'd imagine that in consistent use of a mechanical LSD, parts that are consistently getting friction would also be very hot.

 

[catso]

I and many other BMW owners use Royal Purple Synchromax in my manual trans with excellent results.

 

[TheRuss]

Originally Posted By: JHZR2
Ok but I'm seriously asking - what's the difference in dynamics that makes the one better? Sure people demand the old standard, which surely has much to do with it.

But a rotor with a bake pad clamped down sure can stop a wheel and hold a vehicle well. And there is more friction surface, I'll bet.

I know when we were in a lot of snow in friends' CRV, it stunk bad from the use of brakes as an LSD. But I'd imagine that in consistent use of a mechanical LSD, parts that are consistently getting friction would also be very hot.


So you think that they use them in race cars because of nostalgia? Braking a wheel is never gonna be the best thing for acceleration. A real LSD doesn't need to brake a wheel to transfer the power. You'll get better traction and acceleration with a real LSD, among other things. I'm sure there's plenty of info online, but an e-LSD really isn't a substitute for a real one.

Anyway, we're rather off topic now.