[Yoully]

My 2015 435i is on 134,000 miles and has not had the transmission fluid changed. I’ve read/watched a lot about changing or not changing the transmission fluid on high-mileage ZF 8HP due to causing more harm than good. The gear changes feel fine, no harsh changes, no slippage that I’ve felt.
I’m wondering if there is a cut-off point, after which I should just leave the old oil in, or if there are any signs I can look for to determine if I should change it?
Also, I recently changed the HPFP, so I took the opportunity to get a look in the air intakes. Looking at the photo below, do you think I’m due a walnut blast or can I hold off?

[Billfitz]

Don't believe everything you read, especially on line. You won't hurt the tranny with a fluid change, provided it's done correctly. You valves aren't that bad, use this to clean them up. https://www.crcindustries.com/gdi-iv...valve-cleaner/

[Jvac]

Originally Posted by Billfitz

Don't believe everything you read, especially on line. You won't hurt the tranny with a fluid change, provided it's done correctly. You valves aren't that bad, use this to clean them up. https://www.crcindustries.com/gdi-ivd-intake-valve-cleaner/

That stuff actually work just by sending it through the intake, or do you need to get it directly on the valves?

[Jvac]

Originally Posted by Yoully

My 2015 435i is on 134,000 miles and has not had the transmission fluid changed. I’ve read/watched a lot about changing or not changing the transmission fluid on high-mileage ZF 8HP due to causing more harm than good. The gear changes feel fine, no harsh changes, no slippage that I’ve felt.
I’m wondering if there is a cut-off point, after which I should just leave the old oil in, or if there are any signs I can look for to determine if I should change it?
Also, I recently changed the HPFP, so I took the opportunity to get a look in the air intakes. Looking at the photo below, do you think I’m due a walnut blast or can I hold off?

I thought about skipping the service once I got past a certain point for the same fears you describe. But, people wiser than me have pointed out that there are more documented cases of failure in transmissions when the fluid isn't changed. Any fluid will eventually fail. Then the tranny will go along with it. Replacing the fluid, if done correctly, is the way to ensure longevity. At some point, the fluid degrades enough as to no longer be effective and then the metal parts start wearing on each other. The only way to know is to drain the fluid and inspect. If there's excessive metal buildup in the fluid or pan then a rebuild is recommended. If that's what you find then it was likely going to fail soon anyway. Leaving the old degraded fluid in there won't extend the life of the tranny past the failure point, despite what the service advisers at the dealerships say. They are most likely trying to cover their asses in case the service is botched or the transmission is worn beyond repair

[scubajim]

I agree a simple drain replace the filter and cover and refill is harmless and necessary. I have heard of a power flush which I think would be a risky procedure but even then, who knows.

[cfm56d7b]

ZF recommends fluid changes every 8 years or 50K miles whichever comes first.

Since there are no apparent symptoms of transmission wear (slippage, harsh shifts), changing transmission fluid + pan + filter would my recommendation. Use Lifeguard 8 transmission fluid.

However, who performs the fluid change and how makes all the difference.

Keep in mind that changing the transmission fluid does not mean that all fluid will be replaced. It takes 3 drain-and-fill cycles to replace about 80-85% of transmission fluid.

There are persistent myths which suggest that changing the transmission fluid can make things worse in a high mileage transmission. What is more likely instead: an improper fluid change leading to air pockets and component failure.

[Yoully]

cfm56d7b I’m glad you’re pointing this out! I was under the impression that I could simply drain off the old fluid by removing the plug(s) remove and replace the filter cover and refill the though the filling port.

[cfm56d7b]

Originally Posted by Yoully

cfm56d7b I’m glad you’re pointing this out! I was under the impression that I could simply drain off the old fluid by removing the plug(s) remove and replace the filter cover and refill the though the filling port.

The ZF transmission fluid change procedure is very precise, has multiple steps, and not for a novice. Please study all steps prior to doing anything.

[cfm56d7b]

Although this topic has been discussed extensively in many forums, it's helpful to share why BMW suggests that transmission fluid lasts a lifetime while ZF - the actual manufacturer of the transmission - suggests that transmission fluid has to be replaced at a certain interval.

ZF sends to BMW ready-to-install, fully assembled, sealed transmissions with all the fluid inside. BMW just installs it.

So why a difference in guidelines?

- In BMW speak, lifetime means around 100K miles
- Many cars are leased
- Most cars are sold prior to reaching 100K miles
- if BMW indicated that transmission will require services at 50K-60K miles, the consumer will see it as a future, potentially expensive required maintenance item
- BMW does not want to include transmission fluid change in service packages
- Warranty cost control: the transmission has to survive the warranty period or an average lease / ownership cycle

ZF transmissions have very tight clutch tolerances. The fluid will degrade with age and heat. So it has to be changed.

If you plan to keep you car beyond 100K miles, simply change the transmission fluid and find a shop that knows how to perform this procedure correctly.

[Yoully]

ZF 8HP Service Guid

Having looked through the service guide it seems strait forward. Unless there are any steps missing from this guide?

[Jvac]

Originally Posted by Yoully

ZF 8HP Service Guid

Having looked through the service guide it seems strait forward. Unless there are any steps missing from this guide?

That's the right document. Car must be on level surface or lift, run through the shifts as it states, and the big thing is to have the correct temperature before final filling. Fluid needs to be circulating through all the lines and coolers in addition to what's in the pan. Most common problems are related to underfilling because they didn't observe this part.
Zf has a video somewhere on YouTube demonstrating the service; might be helpful to watch them do it.

[perezr10]

I had an E90 with the 8-Speed Auto and I changed the ATX at 115,000 and never had any issues after that.