My 2003 Toyota 4Runner is a V6 SR5 4×4 that has a non-sealed transmission unit. This system has a transmission fluid dipstick, unlike the later years’ 4Runners that have a sealed transmission with no dipstick. The following procedure outlines a flush and fill of the transmission fluid for my car:
First, remove the 14mm drain plug and let all the transmission fluid from the pan drain out. After everything had drained out, I replaced and tightened the drain plug.
I could find very little information online about the gasket that is needed for the transmission fluid plug. So I chose to go into my local Toyota Dealership’s Parts Department to ask for the gasket, which they were very willing to help with. I also picked up the OEM Toyota transmission fluid as well.
You can use any sort of drain pan to catch all of the fluid that comes out (about 4-5 quarts.) This kind of drain pan works nicely:
Purchase on Amazon.com: Capri Tools CP21023 Portable Oil Drain Pan, Anti-Freeze, Green (affiliate link)
For the sealed transmission of later years, the recommended fluid would be the Toyota WS Fluid. However, with non-sealed transmissions like mine, the fluid to use is the ATF T-IV Fluid from Toyota. I purchased a dozen quarts of the fluid as I would be using about 5 quarts to refill the transmission pan, and the remainder on flushing the radiator cooler lines.
Below are links to purchase by the quart or for a dozen quarts (cheaper option):
Purchase on Amazon.com: Genuine Toyota (00279-000T4-01) Automatic Transmission Fluid (affiliate link)
Purchase on Amazon.com: Genuine Toyota Lexus ATF Type T-IV Automatic Transmission Fluid OEM 12 quart Type-4 ATF (affiliate link)
In addition to draining the transmission fluid from the drain plug, I also flushed the transmission fluid that runs through the oil cooler lines to the radiator. There is an inlet oil cooler line and an outlet oil cooler line, both running between the transmission and the radiator. I removed the outlet cooler line on the radiator side, and used a 3/8″ clear hose to attach to the metal piping. The other end of the clear hose was run to the drain pan. This post helped me greatly with identifying the proper line to use.
I turned on the car for about 10 seconds (not allowing the car to warm up) so that additional transmission fluid would leave the radiator and exit through the oil cooler outlet hose. I then refilled another 2-3 quarts and re-did this several times to “flush” out the fluid. When I was finished, I removed the clear plastic hose, connected the oil cooler outlet hose back to its place, and then prepared to refill the transmission fluid to its permanent level.
To refill the transmission fluid through the dipstick, I use a funnel that specifically fits. Normal funnels don’t fit properly as it needs to be narrow enough for the lower-mounted transmission fluid dipstick location.
Purchase on Amazon.com: Plews 75-068 Super Funnel – 2 Quart Capacity (affiliate link)
Finally, refill the transmission with 4-5 quarts of transmission fluid. Turn on the car and let it run until it is warmed up. Then then fill slowly meanwhile checking the dipstick level to get it to the proper level. Then you’re all done!
These two links outline both non-sealed and sealed transmissions and are of utmost value when performing this transmission service on your vehicle. It definitely helped me out a ton: