Originally Posted By: Jax_RX8
I have two words for all those with the 6F35 transmissions to cure your woes - Redline D6.
Now for the supporting data - I am also an owner of a 2012 Fusion, 2.5l, with the 6F35 transmission. I have had this car a little over a year now and have 21,000 miles on it now. I have not had ANY programming updates since I bought the car.
After buying the car, I went to the fusion forum and found out these trans were finicky. I also had the hard 1-2 shift when the trans was cold and the occasional flare on 3-4 shifts. If I drive it more aggressively, this happened less, but still on occasion occurred.
I decided to try out a top notch trans fluid as I was concerned with the longevity of this trans and I intend to keep this car a very long time. So at 10k miles, I substituted 3.7 quarts of trans fluid (using a Pela extractor) and put in Redline D6 (this is the most you can get out of the sump at one time).
I noticed and immediate difference, even though I only replaced about 1/3 of the total fluid. The whole trans was smoother. After running a few hundred miles to allow the programming to adjust, I had no more hard shifts or flares. At 20k, I did the same, and the trans has gotten even better - I have not had a hard shift or flare for over 10k miles since I put in the D6.
While Ford keeps attributing this to programming, I actually think it is more fluid related. This trans is very hard on fluids as you can tell by how quickly it dirties it up and shear it down in a very short period of time. RL D6 is an ester formula that starts at 6.4 cst and will not shear down below 6.1 cst during its life (Ford spec for Mercon LV is not less that 5.5). I think that while MLV is a good fluid, it is not near as good as RL D6, and thus the much better performance of my transmission.
I intend to keep replacing 3.7 qts every 10k miles and expect a long life and very good trans performance on out. If you have a problem now, you might consider doing 2 -3.7 qt fluid changes (with a short drive in between to mix the fluids) and see what it does for you - I bet it will surprise you the difference it makes.
In the FWIW department, I am also using RL 5W20 in the sump (started at 5k miles and doing 5k OCIs) and this engine is much quieter and smoother than it was on the motorcraft 5W20 (still using MC filters though).
This is not a sales pitch and I am a veteran of this site that has used many different oils over the years, but have to say that I switched to RL about 2 years ago (it took me years to try it as I did not believe all the hype) and it has far exceeded what I have seen in ANY other brands I have used, which if you look back through posts you will see a lot of them.
Hope this helps out any 6F35 owners as it sure worked for me.
This is great advice. I may just do this. The only downside is that RL D6 is quite pricey, but if it works, it'd definitely be worthwhile to do.