Is there a significant advantage to replacing Mercon V with Mercon LV ATF? From what I have read, they can't be mixed. So a flush of the AT would be necessary to use Mercon LV.
Only use what the owner's manual says to put in the transmission. If something gets released as being compatible with the OEM fluid by the manufacturer in a Technical Service Bulletin, maybe use it, but that's it. It doesn't matter if you fully rebuilt a transmission and cleaned everything out, it was designed to use a specific fluid, or anything deemed backwards compatible. The transmission in my truck was rebuilt and the shop still filled it with Mercon V. Different fluids have different flow properties, lubrication capability, hydraulic performance, cooling capacity, etc. Incompatible fluids will make the transmission malfunction and possibly damage it.
I was simply wondering if it were possible to completely flush the tranny and use the Mercon LV if and only if it could be done and provided better performance. Gotta be careful with this stuff - Valvoline has a tranny fluid that says it's compatible with Mercon LV but made no mention of Mercon V while Amazon says it's compatible with my 02 Mustang GT and some expert (?) in the Q&A section says it's compatible with Mercon V trannys. Of course, when I researched this, Mercon LV and Mercon V can't be mixed. It seems like Mercon LV is an improvement over Mercon V though. The Valvoline multi-vehicle synthetic is compatible with my Nissan though. I have both SuperTech Mercon V specific fluid and the Valvoline in my garage - I hope I don't grab the wrong container..........
My '99 Ranger says Mercon V only on the dipstick. I put Valvoline Mercon V in, I was exploring a possible over-fill problem and bought a new quart just in case I needed to add fluid back. It hasn't given me any issues, so you're probably good to use it in your Mustang. The only vehicle I've seen firsthand that takes the LV formulation is my girlfriend's parents' 2010 Focus. I'm guessing it's a lighter fluid than V and made for very light duty use. Being a more complex 5-speed auto, it could also be thinner to help flow through the system better. My Ranger is a 4-speed, and I think your '02 Stang is as well. Seals, etc. Could be sources of problems if the additives or fluid base itself messes with old Mercon V seals. That's a problem with different brake fluids. All this is speculative, as I'm not sure why they are actually incompatible, but would probably be some mix of that.
I checked at Valvolines website and it specifically states that the MaxLife Multi-vehicle Full Synthetic ATF is compatible with Mercon LV, Mercon SP and Mercon V (even though the container only mentions Mercon LV). I don't know how that's possible since every source I've read says you can't mix LV with V.
That Valvoline Maxlife Full Synthetic is good stuff. I use it in all my vehicles even my mercedes s500 and they all shift really good with it. I think you can use it with everything but CVT and Ford's.
My 02 Mustang GT takes Mercon V - actually the owners manual says Mercon but Mercon V can be used. Mercon LV on the other hand isn't compatible. It's confusing since the Valvoline website says that MaxLife Multi-vehicle Full Synthetic ATF is compatible with Mercon LV and Mercon V. Since you can't mix Mercon LV with Mercon V, how is that possible?