there seems to be some confusions as to which ATF to use. Here is a general break down. Check the ATF dipstick, and it will specify which one to use.
1. Dex III/IV is for the non-electronic transmission, sort of the pre-99 ES300
2. Type T-IV is for the electronic transmission, 99 ES300 w/VVTi engines or later models
3. If you are confused or uncertain which ATF to use, use Amsoil ATF. It's a synthetic ATF and compatible w/numerous ATF systems. Good for 50K miles. I actually go even longer than 50K on Amsoil ATF because I drive 95% freeway.
By the way, I find it very odd that coolant mixes w/ATF. Typically ATF passes thru the cooling hoses surrounding the radiator and returns into the transmission. Unless you have a crack radiator and crack ATF cooling hoses right at the same contacting point, I find it hard to see how ATF mixes w/coolant. For argument sake, the car might have a front accident impact at that point.