anyone flushed their tranny?

[Lubehead]

Not in my vehicle. I will be changing mine at 50k. One always want to change "good fluid". No sense changing a fluid after it has deteriorated and caused damage-potential or otherwise.

[JCL]

Originally Posted by Lubehead

Actually, I don't think there's anything low grade about modern automatic transmission fluids. In fact they are amongst the most complex fluids available. Automatic transmission fluids typically contain antioxidants, antifoam agents, viscosity modifiers, antiwear additives, friction modifiers, and seal swell modifiers.

Formulations vary from manufacturer to manufacturer with sometimes subtle differences in friction modifier chemistry. The oxidation resistance of these fluids is especially high, allowing the long service life now generally reccommended by most OEM's.

In addition to acting as a hydraulic fluid, these products also lubricate gears and bearings, and must be able to withstand severely low start up temperatures as well as extremely high bulk oil temperatures particularly in severe service like towing.

The high temperatures ultimately take a toll on the fluids life as byproducts of oxidation accumulate in the form of depleted antioxidant inhibitors and contaminants from the clutch plates, as well as oxidized base oil.

Changing the fluid in a timely fashion cannot help but provide extended component life. Keeping the fluid relatively clean and fresh enables it to effectively deal with preventing the inevitable results that would occur if it was not changed. Reduced wear, reduced deposit formation and superior performance in both cold and hot temperatures is ensured by a proactive approach to fluid maintenance.

I don't think there is anything low-grade about these ATF fluids either. I just think that the lubrication requirements are not particularly demanding. That is why a straight 5w oil like an ATF works fine. It is a sealed system, with a pressurized oil bath. It is heated when cold, and cooled when hot. All of the other requirements are very specific, and critical, but they are not as related to the lubrication aspect. And when people talk about changing the fluid, they tend to focus on the lubrication requirement.

I do think that the friction modifiers are more critical than you give them credit for.

I also think that the thermostatically controlled heat exchangers in the X5 deal quite successfully with the high temperatures that used to make transmission fluid changes much more critical.

A lot of the transmission failures we have seen reported have been in the transmission valve bodies. Those aren't caused by lubrication failures. Many other transmission failures have been caused by electrical failures, either wiring harnesses, solenoids, or sensors. I suggest that changing the transmission fluid regularly will have little to no effect on transmission life considering these common failure modes. If we were seeing burnt clutch plates and other signs of overheating, I would fully agree with you that changing the fluid regularly would be of benefit.

[ard]

Originally Posted by Lubehead

Not in my vehicle. I will be changing mine at 50k. One always want to change "good fluid". No sense changing a fluid after it has deteriorated and caused damage-potential or otherwise.

Agree

[diesaroo]

Well according to the attached documentation from ZF, maker of the transmission, the severe service schedule including frequent high speed driving, sporty agressive driving, and/or towing says fluid change every 80-120,000 km or 8 years. So in good ole american miles, 50-75k miles with only the proper fluid listed.

Everyone may not fall into that category, but I think it a good idea to be preventative and follow the earliest manufacturer recommended change at 50k miles.

Also interesting to note the recommended fluid is not fully synthetic, but a blend.

[Lubehead]

Diesaroo, which transmission is in our 35d's?

[diesaroo]

Originally Posted by Lubehead

Diesaroo, which transmission is in our 35d's?

Well the 6-speed automatic in the E70 is the GA6HP26ZTU. This I interpret corresponds to 6HP26X in the document.

I am not sure of the 8-speed designation, but according to the ZF publication that I posted, they are both under the same interval.

[JCL]

Originally Posted by diesaroo

Well according to the attached documentation from ZF, maker of the transmission, the severe service schedule including frequent high speed driving, sporty agressive driving, and/or towing says fluid change every 80-120,000 km or 8 years. So in good ole american miles, 50-75k miles with only the proper fluid listed.

Everyone may not fall into that category, but I think it a good idea to be preventative and follow the earliest manufacturer recommended change at 50k miles.

If you want to change your fluid to be as conservative as possible, that is fair. It is your transmission, and your call.

However, you are taking the guidance of the component manufacturer over the guidance of the system manufacturer.

The document says that very high fluid temperatures will age the fluid prematurely, and I fully agree. It then goes on to say that various types of severe service (as listed above) can cause such high temperatures, justifying early changes of the fluid (every 65,000 miles or 8 years). One thing to keep in mind is that BMW addressed the high temperature issue with the cooler that they designed in to the vehicle. We can discuss whether or not that cooler is sufficient I suppose. I would be more worried about high ambients, trailer towing, etc, if that cooler wasn't there. It is because of the total system design (the cooler, the engine software that backs off engine power momentarily to soften the shifts, the torque converter lock-up clutch strategy that reduces heat from the torque converter, etc) that I would look to BMW's guidelines as more relevant than ZF's.

It would be interesting is to see what actual fluid temperatures climb to compared to ZF's application guidelines. If the BMW cooler isn't able to maintain them within ZF guidelines, then the ZF fluid change recommendation would be very relevant. If the BMW cooler is able to maintain fluid temperatures to the design specification, then there is no severe service recommendation applicable.

[diesaroo]

Originally Posted by JCL

If you want to change your fluid to be as conservative as possible, that is fair. It is your transmission, and your call.

However, you are taking the guidance of the component manufacturer over the guidance of the system manufacturer.

The document says that very high fluid temperatures will age the fluid prematurely, and I fully agree. It then goes on to say that various types of severe service (as listed above) can cause such high temperatures, justifying early changes of the fluid (every 65,000 miles or 8 years). One thing to keep in mind is that BMW addressed the high temperature issue with the cooler that they designed in to the vehicle. We can discuss whether or not that cooler is sufficient I suppose. I would be more worried about high ambients, trailer towing, etc, if that cooler wasn't there. It is because of the total system design (the cooler, the engine software that backs off engine power momentarily to soften the shifts, the torque converter lock-up clutch strategy that reduces heat from the torque converter, etc) that I would look to BMW's guidelines as more relevant than ZF's.

It would be interesting is to see what actual fluid temperatures climb to compared to ZF's application guidelines. If the BMW cooler isn't able to maintain them within ZF guidelines, then the ZF fluid change recommendation would be very relevant. If the BMW cooler is able to maintain fluid temperatures to the design specification, then there is no severe service recommendation applicable.

The thing is, we'll never know. I have never seen a modern vehicle without a transmission cooler. If we can take that as fact, I think ZF is providing the severe service schedule with that in mind.

Now if BMW installed a larger transmission cooler or an auxiliary cooler as part of the tow package, I might be more apt to agree. But they don't. Also, why has BMW not included transmission fluid as part of CBS? This tells me they are not tracking individual fluid condition that may vary widely depending on usage: towing, aggressive driving etc.

Another part of the equation that you have to think about is: who stands to profit if your transmission fails prematurely? I guess you could include ZF since they're providing the transmissions, but I think we would all agree BMW dealers have more to gain.

So, maybe I'm a little conservative, but I count the ZF people to be a little more accurate in this case.

[JCL]

Originally Posted by diesaroo

The thing is, we'll never know. I have never seen a modern vehicle without a transmission cooler. If we can take that as fact, I think ZF is providing the severe service schedule with that in mind.

Now if BMW installed a larger transmission cooler or an auxiliary cooler as part of the tow package, I might be more apt to agree. But they don't. Also, why has BMW not included transmission fluid as part of CBS? This tells me they are not tracking individual fluid condition that may vary widely depending on usage: towing, aggressive driving etc.

Another part of the equation that you have to think about is: who stands to profit if your transmission fails prematurely? I guess you could include ZF since they're providing the transmissions, but I think we would all agree BMW dealers have more to gain.

So, maybe I'm a little conservative, but I count the ZF people to be a little more accurate in this case.

What is really cool is having a very civil discussion about this. That hasn't always happened on threads on this topic.

Using the towing example, BMW has sized their transmission cooler for towing up to 6000 lbs, in high ambients. What percentage of your driving is under those conditions? I think that if BMW offered a larger cooler for towing, then we could reasonably infer that the standard cooler is closer to 'standard conditions'. On other models (primarily E53) we saw well documented examples of a member towing 8000+ lbs over the continental divide repeatedly. No transmission issues in 80,000 miles of vehicle use in that case. So, I have a suspicion that the cooler is adequate.

I think that ZF is simply covering their ass, as many manufacturers would. They don't give specific criteria, they just say that the fluid is good for the life of the transmission, but it is possible for some people to overheat the fluid requiring a change after 8 years.

Agree that BMW isn't using condition based service on the transmission fluid. Given their predisposition to do so on other fluids, including the transfer case, maybe they just can't see the need.

If your transmission fails early, I think the dealer is least likely to profit. Few owners would choose to buy a new transmission when rebuilds are available, and dealers don't offer any repairs, only replacement. They aren't in the transmission business. Dealers won't get the parts and service revenue, and if there are too many failures, they stand to lose sales. BMWNA isn't in the transmission repair business either, they carry replacement transmissions for use during the warranty period, but I don't see them selling many outside of that term. They essentially abandoned that market. ZF is the only one who stands to gain in multiple scenarios, whether they sell their rebuild kits to remanufacturing places working for BMW, or to independents buying kits to rebuilt individual transmissions.

It isn't a bad thing to be conservative about this. If I planned to keep an E70 for 10+ years, I could see changing the fluid, probably around the five year mark.

[ard]

Originally Posted by JCL

If you want to change your fluid to be as conservative as possible, that is fair. It is your transmission, and your call.

However, you are taking the guidance of the component manufacturer over the guidance of the system manufacturer.

The document says that very high fluid temperatures will age the fluid prematurely, and I fully agree. It then goes on to say that various types of severe service (as listed above) can cause such high temperatures, justifying early changes of the fluid (every 65,000 miles or 8 years). One thing to keep in mind is that BMW addressed the high temperature issue with the cooler that they designed in to the vehicle. We can discuss whether or not that cooler is sufficient I suppose. I would be more worried about high ambients, trailer towing, etc, if that cooler wasn't there. It is because of the total system design (the cooler, the engine software that backs off engine power momentarily to soften the shifts, the torque converter lock-up clutch strategy that reduces heat from the torque converter, etc) that I would look to BMW's guidelines as more relevant than ZF's.

It would be interesting is to see what actual fluid temperatures climb to compared to ZF's application guidelines. If the BMW cooler isn't able to maintain them within ZF guidelines, then the ZF fluid change recommendation would be very relevant. If the BMW cooler is able to maintain fluid temperatures to the design specification, then there is no severe service recommendation applicable.

So lets take this conversation to the extreme-

Lets say, for the sake of argument, that we agree that the conditions that are outlined in the ZF document are never achieved in our use. So never high temps, never towing, etc, etc....

The logical conclusion per the document is that the fluid will last FOREVER... how is this possible? It is flat out nonsense. I dont care if it it 100k miles, or 10 years, or 20 years or 50 years.... it is NOT POSSIBLE for oil to last forever. And for BMW and ZF to 'pretend' this is true is disingenuous.

Now, that brings us to the 'space' betwee 'forever' and '8 years or 80k KM'... I believe that degradation and damage to molecules is cumulative, and os not a binary event- it is illogical to imagine that as long as you do not hit those stated conditions that fluid will therefore remain unchanged....


One thing we can agree on is this: vanishingly few of those reading these posts today will own the car when issues with ATF come home to roost. (They will fail for other reasons, or owners will just move on.)

Finally, I am 100% convinced that the "system manufacturer" does NOT have OUR best interests at heart, and is not driven by the primary design control input of 'longest transmission life'. (IMO, they are driven by 'lowest overall ownership cost to first retail purchaser', 'lowest maintenance cost to BMW', 'lowest repair rates to BMW'...etc.)

Say, haven't we been here before?

A