Synthetic Oil for 4R100 transmission

Royal Purple, Redline, among others.

Do a Google search and read up, decide for yourself.

Change it when it's warm. It'll feel better running down your arm.

Spdloader

Walmart carries Mobile SYN ATF for under 6 bucks a quart. Not sure what is gian by it though because even though it can take more heat, the tranny seals cannot so if you service regularly with regular ATF and keep it cool it will last just as long (or longer if you do not regularly service it and keep it cool with SYN)

----------------- The SnoMan

I have been using Amsoil since 1987 with out any failures on any equipment until I jacked up horsepower on my 97' F-350 crew. At 160,000 the rearend bearings along with tranny have been replaced. All my fault. My 1986 350 crew with 485,000 still has all original parts. No other equipment failures on the ranch except the 97'.

I have had no failures at all in any automatic for 30 years and I have towing, plowed snow and traveled mountain passes many time in summer heat and I just you plain old dino ATF. The trick is keeping it cool and keeping fluid fresh, not that it has to be SYN. I have a 27 year old THM400 in a J20 that has had its butt worked off for years and started its life as a farm truck and then pushed snow for many years and tranny still works like new and snow plowing is hard on a tranny too.

----------------- The SnoMan