Here's a little update. I finally had a chance to dive into the O2 sensor. It was failing silently so it was not throwing a code. Until recently. A few times the engine light came on then off. I replaced it and sure enough the O2 sensor was responsible for 95% of my issue. There's still a little something going on but it's incredibly minimal and may be due to residual or learning issues.

I'm going to replace the other matching O2 sensor as well since they tent to fail around the same time. But with 255k on the clock, with original O2 sensors, I'm not complaining. I'll b replacing all of them over the next few months but at $150 a pop I'm going to take my time.

Crazy that the O2 sensor could cause such an issue to feel like my transmission was dead. I learned something new.

Very cool.

Going back to changing Transmission fluid. IMO the fluid and filter should be replaced about every 50,000 miles. Since changing the fluid doesn't empty the torque converter I remove the pan, change the filter and refill with new fluid. Drive 25-50 miles and then drain the fluid and refill with new fluid a second time. I use only the designated fluid for the transmission.

So after totally derailing this post because of that phantom failure of the O2 sensor, and now that I have that fixed, the car is running beautifully. So I'm back to my original question, should I or should I not proceed with a transmission fluid change?

As mentioned, the X has 255k on the clock and the original fluid. It runs and drives mint! But I fear if I drain the fluid, and add new fluid that the transmission will begin to slip.

I know some say that there's a certain group that says no matter whet milage, change the fluid! But what are your thoughts?

I'm leaning toward doing it, but, I wonder if perhaps I can pull the fill plug, suck some fluid out, then have the fluid tested before proceeding with the full change. This will only loose a little fluid but will show if it's filled with friction material? Thoughts on this?

Thanks!

Change it. Do a 2x 'drain-fill-. Change all the rubber bits and bridges too.


It may die in 10k. If you do the fluid change you will declare "it was doing the change that screwed me" if you DONT, you will declare "a fluid change might have saved it"


You are doing a gentle drain/fill...and NOT a "flush". Dont associate issues that can come up with an aggressive power flush with a simple fluid change.


Also. O2s are a maintenance item. For a reason. ;) Wonder what that has been doing to your motor? AFRs? Fuel dilation? hydrocarbon loads in the Cats....who knows....

Agree with ard and others. DO NOT FLUSH ANY TRANSMISSION. EVER.

If I were you, I'd drain the pan, remove the pan/filter, replace the seals and sleeve, install a new pan/filter, top off with new BMW OE or real ZF fluid. I said before, you got good miles out of that transmission and you're on the tail end. When it goes, you'll never know if it's because of the fluid/filter change OR if you did nothing.

Now that I've established some level of service with my transmission, I've decided to replace the pan/filter every other "1/2" fluid change which will occur every 50k miles. My transmission is young but coming up on 200k miles with no issues at all during my ownership. I hope this continues.

I'd run some Liqui-Moly fuel cleaner through a couple of tanks. They offer a few different types: Valve Clean, Fuel System Cleaner, Speed Tec Gasoline, Gasoline Engine System Cleaner, Injection Cleaner, which are good. Lately, I've been using Archoil products in my X5d and diesel truck and am pretty happy. Read that as nothing has blown up. Yet. Chevron Techron is a great product, also. Maybe you live in a region where Chevron w/Techron or Texaco w/Clean System3 is available at the pump. Run a few tanks with whatever you choose and then change the engine oil and filter.

You can buy Techron at any auto parts store and add to a full tank of gas.

Nice that the o2 solved most your issues. Always important to eliminate other causes for possible trans problems first.

Change the fluid, rubber seals, and service with Valvoline MaxLife multivehicle. DO NOT USE ZF LG6! LG 6 should only be used on a vehicle that has had regular maintenance. I'm one of the few who have experience with LG 6 on high mileage, not serviced, transmissions (multiple vehicles). Do not use ZF fluid. It's a waste of money and is thin resulting in not maintaining pressures.

That said, at your mileage, as others have said, changing fluid (or not changing fluid) may result in blaming a fluid change for trans errors or other erratic behavior. No way of telling. At your mileage with no service history your trans is a time bomb. If keeping the vehicle, prepare for a trans change financially.

Were it mine. Change with Valvoline fluid, not flush, just drain and fill. Replace bridge, tube, pan/filter, and mech seals. Good luck.

Thanks for the reply! Yes I totally agree on the "time bomb" part lol Stupid me I relied on a "reputable" indie shop years ago when it only had 120. I called them and said I want to change the fluid and they told me "DO NOT CHANGE IT IT'S BEYOND THE 100K MARK". He proceeded to say that at that milage there's too much friction material in the fluid and it will ruin the transmission if I change it. In retrospect I should have just gone with my gut. But a trusted friend told me to call, and they were the "experts" so I listened. Never again.

I know at some point I'll need a new transmission. I have no problem doing that job myself and it will give me an excuse to but a car lift for my shop! Transmission + lift would still be cheaper than having a shop do the job and the lift will get countless uses so it's worth it.

For now however, I'll do the change. That's my upcoming project for a not so cold day.

Can you offer any advice on where to get the kit and a possible brand you would recommend? I know "BMW" OE is the desired but I'm sure there are comparable aftermarket brands some may have experience with.

I'll go with your recommendation as well and avoid the ZF fluid. If I end up having any slipping issues there is the "Instant Shudder Fixx" stuff I could try.

Thanks!

Also, I believe I have the GA6HP19Z transmission. Is that the ZF 6HP?

Again, just trying to find the correct service kit and possibly the mechatronic service pats as well.

Thanks