I've not noticed much forum activity about replacing the transmission fluid. With my X351 having 57K miles and now 13 years old I decided to do a transmission transfusion using the process described by Don B in the X350/358 forum ZF 6HP26 / 28 Transmission Fluid Flush DIY

Method
Don B‘s method is ingenious using the coolant ports to input fresh fluid and dump old fluid. I highly recommend other members interested in doing a transmission fluid exchange to use this process. I was able to create pretty similar connections that fit the ZF6HP26 or 6HP28 like in my car.



X350 forum member Datasports surmised that if you pumped in new fluid it would just get mixed with old fluid before being ejected, so his thought was to drain the transmission prior to the transfusion method. As I wanted to install a new pan, which has an integral new filter, I elected to follow his suggestion. I was able to eject approximately 6L from the pan drain port so knew that when I started the transfusion, this 6 L would be minimally contaminated with the old fluid. When starting the transfusion, I expected old fluid to be ejected before the new fluid but contrary to my expectations the ejected fluid was already mixed with old. So in hindsight, I think I would not deviate from the Don B transfusion method and let the transmission pump eject the old fluid quart by quart until you can see new fluid coming out. Once you’re finished with the transfusion process run through the gears 3 seconds in drive, 3 seconds in park and 30 seconds idling at 2000rpm which Jaguar/ZF recommend to fill the torque converter and for the valve body to be filled with the new fluid. Final step is to verify correct fluid level by measuring fluid temperature at the fill port.

Fluids
Like many other members on the X350 forum I am convinced that Ford Mercon SP is identical to ZF lifeguard 6, except for color. I purchased a box of 12 quarts to do my transmission fluid transfusion.

Some tips, tricks and WARNINGS.
Here’s an important lesson I learned of something not to do. Do not open the fill port unless the engine is running. I mistakenly did this and dumped 2 1/2 quarts of newly installed fluid. I then had to deal with pumping that back in with the engine running, in a very tight space, with an adjacent hot exhaust. So learn from my lesson and DO NOT OPEN FILL PORT WITHOUT THE ENGINE RUNNING.

The fill plug is an 8 mm hex but the space is tight so I cut a 8 mm Allen to suit.




Measuring transmission fluid temperature accurately is a challenge. I elected to take a meat thermometer and bend the probe so I could insert it through the fill hole. As this formed a hook the probe could be suspended monitoring the gradual temperature rise while also viewing whether fluid was dripping out. If others choose to do this, just be careful to not bend the temperature probe more than 45° otherwise it might break the internal wire and no longer measure temperature.




Pumps
Don B trialed various pumps before settling on the Mityvac. I would concur that's an excellent pump and I've used mine exclusively for draining engine oil so I didn't want to risk cross contamination so looked into some cheap alternatives. I ending up using this Harbor-freight pump but would not recommend it as I found it slow, bulky and really needed to operate it much higher than the inlet port to be efficient.


However this Harbor-freight manual pump was quick and effective. You really need to support new fluid containers to avoid inadvertently tipping them over when using this pump.

 

Very nice write up!
Always better with pictures.

One BIG reminder! Get that fill plug loose BEFORE you drain the transmission! That fill plug is real tight and I thought I was gonna break my Allen wrench as I had a 15" cheater pipe on it before it would move. They all are so be prepared.

After doing this service several times and on a couple of different brands of cars I now use a fluid transfer pump for filling. It's more expensive but with the features it has the added convenience is worth it.

The key is the different adapters that come with the kit.





This allows you to get the fill hose adapter in and hang it on the transmission fill port. So it's hands free. I support the pump on a rolling platform under the car. Comes with a 40" long hose so you have some room to work.

I use this adapter on our transmissions. The valve is nice because you can pressure up the pump with the valve closed. Get everything in place and just open and close the valve as needed. The valve is also well away from the boiling hot exhaust that is directly across from the fill plug!





Here is the pump I use. Schwaben 3-Liter Multi-functional Fluid Pump Kit. It's easy to get at all the normal places.




This one runs about $100 or so. It can also be used for brake bleeding if you want. I have not used it for that so can't say how well that works.
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The 6HP28 has tube seals between the valve body "mechatronics" unit and the transmission that are known to shrink up and cause shifting issues. If I were doing a fluid change I would drop and replace the pan/filter, and preventatively change those as well as the harness seal at the top of the trans. They can be done in situ with a little difficulty.