I haven't seen a post for anything about wanting to switch from oem fluid to Mobil1 ATF. I was wondering if it would just be a drain and fill every 1k miles or would it have to complete flushed and refilled. I was planning on getting OEM T-IV from toyota for $6/qt. But if I can get the Mobil1 ATF instead then I'll make the switch. Going to do some maintenance this Wednesday, Oil Change with Mobil1 5w-30, Differential Fluid change with Mobil1 75w-90, and incremental P/S fluid change. This is for a 98 GS400. coming up on 120k and had the car for a year, I know the last owner said the car sat and only driven on weekends so Definitely want to swap out some fluids for fresh.

So question is there anything different going from OEM to Synthetic ATF? Let me know Thanks in advanced!

 

I went with redline synthetic for my old cars transmission, to be honest I dont feel anything, it's important to keep it clean but beyond that, it makes little difference.

It's like asking if you feel a difference when you switched from regular motor oil to synthetic motor oil. There might be a slight difference, but not enough to be sure.