So I'll start by saying that I'm an asshat. Long story short, I decided to pick up a 3500lb travel trailer and drag it 500 miles from NC to NJ with my 2004 V6 T4R. No, I don't have an external transmission cooler. No, I didn't bother to get a transmission temp gauge. And yes, it just had to be a 96 degree day. The cherry on top is that I incorrectly checked my ATF level before leaving and found out after the fact that it was actually low. Like I said, I'm an asshat.

Anyway, I made it home, stopping several times along the way to check the trans temperature (infrared thermometer pointed at the trans oil pan). Each time I checked, it was 225-235 degrees. I knew that wasn't good, but hey, I had to get home. No weird smells or shifting issues along the way, but I think there is a very slight whine that developed which is mostly noticeable when coasting and letting off the gas pedal.

AFTER getting home, I decided to do some research and found out that getting real time trans temp readings was a matter of buying a $23 OBD dongle and a $5 Torque Pro app. Woulda been nice to have when towing the trailer I also decided to check the ATF level and found out the truck needs to be running when checking the level With hot ATF, on level ground, with the truck running, it was on the bottom of the COOL range on the dip stick. Did I mention I'm an asshat? Finally, I've been monitoring the trans temp with the Torque Pro app just driving around town and the temps seem high, which leads me to believe I may have an issue. For example, today it's 90 degrees out. With an empty truck, not towing anything, just driving around town, the temp was 205 degrees.

Sooo... given all of this, what are the odds my transmission is smoked? Are there any ways to find out before embarking on a camping trip out west and potentially getting stranded somewhere? I was planning to drain whatever comes out from the trans oil pan and send a sample to Blackstone for analysis. Maybe it's also worth dropping the pan to see what the magnets/filter look like? Any suggestions would be much appreciated

When the transmission went in my 03, it was because the transmission cooler broke.

Its interesting your fluid is low. there may be a small/ slow leak somewhere. or potentially the transmission or gasket or another line of the transmission

If its still shifting, youre not out of luck yet. if youve got the ability to drain and fill not a bad idea, consider replacing the pan/ gasket

Good luck

I wouldn't jump to such an extreme conclusion based on what you stated, just service the transmission add some sort of additive for some peace of mind and go on with you life.

I tried this product a few years back when I started having issues with my 4th gen, can say it bought me a few months to gather parts to have it rebuilt
Highly Friction Modified ATF Supplement - Lubegard

I've never had the chance to try any sorts of obd2 apps or scangauge type scanners on my 03 4thgen something about the protocol it uses (can't remember) I have to use a full on scanner to get her to see if everything's good which it usualy is.

On my Prado150 scangauge reads around 195 under normal driving condition and can get to 225 on a hot day after long trips

good luck

I would just top it off and then do a few drain and fills. Yours an 04 so will need Type-IV fluid or equivalent. I've had success using Amsoil signature series ATF.
What color is your fluid? If its still red and doesn't smell burnt you should be good.

Just do a full flush on it, top it off and call it good.

My sisters 07 v6 4x4 went into limp mode and through an atf temp light on the dash. Got it home after another 800+ miles through the mountains, ordered a trans cooler. Went to do the fluid flush and found, no joke, a factory plug sealing on the inlet of the heat exchanger in the radiator. As far as we know, it ran for 150k miles without any external cooling. Its now got over 200k and its going strong.

Impressed or really angry, Undecided 07 transmission situation

@pudzley - Where are you with this? Curious to see how it turns out. Your truck, your call, but here's my 2 cents since you asked. I think your transmission is fine. My reasoning:

1. Yes, the fluid was low, but you didn't do anything out of the ordinary in terms of the truck's design envelope. It's made to tow 3500 lbs. 500 miles on hot days.
2. As for the fluid level, I think manufacturers build in some stoutness for contingencies like this.
3. A temp of 235° isn't even on the high end. According to the Toyota chart below, the A/T OIL TEMP warning light comes on at 302° F. Plus you had no issues and no weird odors. So, discounting the unlikely case of the light being inoperative, the fluid didn't get hot enough that the truck needed to alert you.
4. You have the advantage of a dipstick and can wipe it with a clean white rag or paper towel and see how the fluid looks and smells. We with the sealed transmission have to jump through some hoops to get a look at ours. LOL

Given your situation, investing ~19 minutes to watch this Car Care Nut video would be a great use of your time. The guy is a straight-shooting Toyota master tech who knows his business and he answers all the transmission questions that you see swirling around the web, from fluid type to change intervals to drain & fill vs. full exchange. Bottom line: if it was my truck, I wouldn't go straight to additives, I would do a series of periodic drain and fills with the correct Toyota fluid. If no issues come up, count yourself blessed to have a truck as well made as 4th Gens are.

Edit: Found this in the FSM. Note there's a typo in the top "Detection Condition" box; 150° C is 302° F, not 275°. The next box is correct in that 135° C is 275° F.