I found this interesting TSB released by Toyota regarding their T-IV ATF:

http://www.ncttora.com/fsm/2000/Service%20Bulletins/tc001t02%20ATF%20Fluid%20Requirements.pdf

TSB: TC001-02
Title:
AUTOMATIC TRANSMISSION FLUID REQUIREMENTS
Models:
All ’00 – ’02 Models & ’03 Corolla & Matrix


MODEL----- 2000 -----|---- 2001 ----|---- 2002 ----|---- 2003
Corolla A131L, A245E | A131L, A245E | A131L, A245E | A245E
ATF----- DexronIII --|-- DexronIII -|-- DexronIII -|--- T-IV


Look at the row for the Corolla. The columns are the Aisin automatic transmission model numbers. Toyota recommends Dexron III in the A245E AT before and including 2002. However, Toyota goes to recommend Type T–IV in the SAME... I repeat the SAME 2003 Aisin A245E AT. There might be some very minor improvements in the AT from year to year. But I doubt anything significant enough to require an ATF with entirely different characteristics. Which leads me to conclude that T-IV is perhaps a higher grade Dexron III. I am speculating that they did this so they can promote their "life time ATF" to raise the Corolla value's because of less maintenance. And would also explain Toyota's naming convention (4 comes after 3) for their improved Dexron III+ ATF.

Here are a few after market ATFs that claim meets T-IV specs and the reason they meet T-IV is because they are already meet Dexron III specs... again this statement is sepeculation:

Mobil 1 Synthetic ATF

Mobil Multi-Vehicle

Mobil ATF 3309 (approved against Type T-IV, JWS 3309)

CASTROL Import Multi-Vehicle

PENNZOIL MULTI-VEHICLE

If the above is true then that would leave a lot full synthetic and synthetic blend alternatives for T-IV ATF users. I believe T-IV is still a conventional as people here and on other forums have stated.

Do YOU agree with what I said?

I forgot to list everyone's favorite alternative ATF which does meet Dexron III and Toyota Type T-IV (JWS 3309) specs:

AMSOIL Synthetic Universal Automatic Transmission Fluid

Oh Cheezus... here we go.

I don't know... there's a lot of extrapolation from one small observation in there... I don't necessarily agree that Toyota should keep its customers to its own brand, but for what I pay for it it is really good value. down here it is close to the cheapest stuff... the aftermarket names claiming to meet T-IV specs are more expensive than T-IV from the dealer, so why bother?

Er, because you may want a better fluid? If I want a basic T-IV fluid that costs less than the dealer fluid, I will use one of 2 SuperTech ATF's at WM that list the spec. Otherwise I use Mobil 1 or Amsoil. All work very well.

Perhaps I am not following the paragraph above, but Type-IV is not a lifetime fluid. The Toyota WS (believe it stands for World Standard) is the fluid they claim is good for the life of the tranny.

here we go what?

Well, T-IV is dino oil with dubious quality (gray color in 20000-30000 miles). Most replacements are synth with proven quality.

I like this info. I have left over Mobil 1 ATF from my previous car. I will go ahead and use it in my Corolla in the next ATF change (drain and refill I do every 30000 miles).

Royal Purple MaxATF also handles T-IV. I will run it in my tranny that calls for T-IV when I have the fluid changed.

Well, let's look at a couple of things here first.

1) The 2003 Corolla is the newer version of the Corolla. 2002 was the last year of the Corolla/Prism versions. So maybe Toyota made some changes to the Corolla/Matrix/Vibe tranny to require T-IV.

2) Mobil 1 is no longer DexronIII/Mercon, it's Mercon V now at least in my neck of the woods. And the bottle that Im holding in my hand as Im writing this doesn't say anythinhg about being used in a Toyota as a replacement for T-IV but can probably be used in Toyota auto trannys using Dexron.

I haven't seen any new Mobil 1 syn atf in my area that states what sunfire is saying. I do beleive sunfire and I would like to see/use this Mobil 1.

According to the Mobil 1 website their Mobil 1 ATF does not mention anything about Toyota T-IV so it should not be used. End of discussion.

Amsoil ATF does mention T-IV and should be an excellent choice if you want a top tier full synthetic.

I have 2003 corolla. The changes in engine mostly dealt with oil consumption (very common in 1998-2002 corollas) such as new oil rings and oil holes. I doubt there were significant changes in tranny, except for software and shifting points. Possible optimized for the new fluid.

As for Mobil 1 ATF suitable for T-IV is shown here:
http://www.mobil.com//USA-English/Lubes/PDS/NAUSENPVLMOMobil_1_Synthetic_ATF.asp

I doubt the formula changed regardless what is printed on the bottle.

It's not end of the discussion if you read here:
http://www.mobil.com//USA-English/Lubes/PDS/NAUSENPVLMOMobil_1_Synthetic_ATF.asp

?

Nice find, from what I remember, M1 ATF was not always a replacement for T-IV. Is this a new formulation? Who will be the first to try it?