I'm familiar with the fluid level check procedure, but something odd has happened both times I've done it. FWIW as you read this, I'm using OBD Fusion to verify the fluid temp.

One of the ATF exchange threads suggests removing the overflow plug with the engine cold, swapping out the crush washer, and replacing it finger-tight so it's good to go once the level is correct. I did that the first time I exchanged my fluid, thinking little to no fluid should come out when it's cold. I still put a bucket under the plug since better safe than sorry, right? To my surprise, about 3/4 of a quart came out. The last person in there was a dealer tech when they did an exchange at 114K so I figured they must have left it overfilled somehow.

But then, once it got into the temperature range for checking, nothing came out and I had to add almost 2 quarts until there was a flow. Huh?

Fast forward to today, when I needed to get the level correct after installing a Derale temperature sensitive valve that bypasses the external cooler unless the fluid temp tops 180° F. I removed the fill plug with the fluid cold - I mean the truck has been in the garage for 24+ hours cold - and a quart of fluid comes out again. And again I warm it up to the proper temp range and nothing comes out until I add a quart and a half of fluid back in.

This makes absolutely no sense at all, in fact it seems 100% backasswards since the fluid level should be higher when warm. What am I missing here?

It's spread all around the transmission not sat in the 'sump'?

Of course. In fact, IIRC many vehicles with transmission dipsticks are checked with the engine idling. So unlike with oil, the manufacturer’s intent must be for the level to be checked with the fluid circulating. Now I have to go back to the post suggesting to replace the overflow plug crush washer straight away and see if I misunderstood.

In any case, I won’t be doing that anymore.

Leave the plug in until you reach 110* then open the level plug. Its also a good idea to run it thru the gears to distribute the fluid in the tranny. Rev the engine to 2000rpm. At 110* you can open the plug and add fluid if needed. When the engine is cold and engine off the fluid drains back to the pan from the cooler. So fluid will drain out as if its over full.

The temp range for testing is 106-113* F.

How much fluid does your cooler hold?

Only pull the overflow with it off if you are planning to change the fluid. When I just flushed mine a few weeks ago a good bit came out opening it with the engine off, but that was my intent since I was flushing it. When the engine is on the torque converter and all that fun stuff is filled with fluid, when it's off the fluid collects in the pan and comes out the overflow.

I also recommend just putting the vehicle into the temperature check mode using a jumper and the process outlined a few places on the forum. There is a lot of misinformation out there about the temperature range to check the level at. Putting it into temperature check mode isn't hard and you know you are in the specific range the car was programmed for by Toyota.

I appreciate your point but my temp range info is straight from the FSM and using the app is much easier. With that said, maybe I’ll try it at my next fluid exchange.

Like others have said, don’t pull that check plug cold and not running. The fluid is all sitting in the pan.

When you start it and let it warm up the fluid is being moved by the pump through the transmission and torque converter non-stop. Every time you pull that plug cold, you’re just causing yourself more hassle of topping off, checking, and dealing with all of that for no reason.

Now, if you have bypassed the cooler system until a certain temp, it’s also going to force you to run lower fluid than you really should when it’s hot. I don’t know why you would want that to happen, but to each their own. Transmission fluid can never be too cold. It’s probably safe to say the cooler system runs almost a half quart through it, which would leave your whole system a half quart low when it cycles.

All this makes me glad I have a trans dip stick!

The valve is designed to run 10% of the fluid through the external cooler all the time, maintaining constant system pressure. It only opens up when more fluid needs to go through the external cooler to keep the temp at 180°.

Not to get into it here but I used to think the same thing but tuns out there’s a debate about whether transmission fluid can be overcooled.

I'm just doing my once a year visit to the thread (I'm half joking... but life doesn't seem to give me time to hang out here as much as I used to...)

Yeah, just get it within about 5-10°F of the fluid check temp before you pull the plug, also make sure the engine is running with the A/C off so it's within the correct RPM range. If the vehicle is off and/or the RPM range is off, it will be in accurate, how inaccurate? I honestly can't say? It seems like being 5-10°F too low or two high probably won't hurt anything (I mean it'd be like what, a few table spoons of fluid?) But I have noticed on some transmissions that when they get closer to the middle/upper end of their temperature check range there's something that opens up like a thermostat or valve and they flow a bit more (I never bothered to look into what it is, just made a mental note of it).

My usual process with transmission services is to overfill about 1/4~1/2 a quart, get the vehicle within 5-10°F of the minimum temp spec, pull the check plug; watch the fluid until it hits about the middle/upper 2/3 of the spec and then install the plug when it dribbles barely.

One thing I will note is that on all our vehicles that have a factory thermostat valve, it is required to lock the valve in the "open" position, this is to reduce the likely hood of air bubbles and encourage even fluid heating. Not sure if your aftermarket cooler allows you to do that or if you need to do that, never deal with an aftermarket cooler that had a thermostat valve, most of the ones I see customers install are just inline trans coolers.

On a side note, it is possible to have a transmission run too cool which will reduce it's efficiency and performance, but I'm not sure or aware of any instances where it has damaged a vehicle.

Thanks, great info as always.

The valve and the cooler are both in line, the fluid goes to the valve, which always allows 10% to go through to the cooler so it’s accounted for when you measure the fluid level. The valve only allows more fluid to go through to the cooler when the fluid temp exceeds 180°.

This is the valve. Lines coming out of the left side go to the cooler.



Here’s the cooler.




Frankly, it’s total overkill for normal driving, but I plan to keep this truck forever and eventually to tow a travel trailer. So I decided to go ahead and get all of this done since I was doing a fluid exchange anyway. I added the cooler when I did the exchange a couple of months ago and should’ve added the valve at the same time but oh well, it’s done now.

Just as a side note on this topic, hottest I’ve seen my fluid temp before the cooler installation was 209° during some summer off-roading.

Yes, there is...including, it turns out, from me earlier in this thread. I would have sworn that I verified the range in the FSM as 97°-115° F when I did my fluid exchange, and that's the range I used. But I just checked the FSM and the correct range for the A750F transmission in my '07 Sport is actually 115°-130°.



Apologies to anyone who was misled by my incorrect information.

It's not just you. There's different temperature ranges written into different versions of the FSMs for some reason. I wanted to do it with just the OBD reading, but I kept finding conflicting answers in both the FSMs and forums. This is why I recommend the temp check mode. There's 3 ranges posted in this thread alone...

And I bet if you were to put your 4Runner into temp check mode the light would come on at the 97-115* range. I just did a flush on my 08 V6, an 05 V8, and a 13 FJ. All of them 4x4 with the A750F. The light came on for the temp check mode, the fluid level was checked, plug installed, and then I plugged my OBD scanner in and checked the torque app. All of them were about 102* which makes sense since they ran for a few minutes after the light came on.

So for what it's worth, there are multiple temperature specifications for multiple years/models.

For example a 2007 Tundra with the AB60F calls for a check temp range of 115°~133°F, while the 2008~2021 model years with the same transmission call for 99°~113°F.

I don't really have a good answer for the variation beyond I am assuming some sort of inline production change (similar to how 1GR-FEs in 4Runners went from a 2-wire Cam sensor to a 3-wire with no actual change in the engine designation/architecture)

I have no idea where you got that screenshot with the blue text. You don't usually see blue text in the older Toyota FSMs and looking at both the FSM for a 2007 4Runner (2007_4Runner_ATF_Check.pdf) it states that the range should be 97°~115°F for both the A750E & A750F. Additionally T-SB-0129-08.pdf has a chart that shows ATF temperature ranges for a handful of 2004-2008 Model Years that were using WS ATF at the time (as far as I can see there isn't a supersession to this TSB, so the information should still be accurate).

~

I will say that I normally don't give the ATF temp ranges too much thought as I just pull up the specific year/model FSM and look up the temp for each vehicle I am currently working on (specifically because of the variations). Though I will note that the FSMs for newer vehicles will occasionally include a section for "High-Temperature Check," but I haven't seen that applied to older A750's, mostly seen that for the transaxles.

The fluid is circulating around the trans when running so if it sat idle you would have all that draining back down into the pan. Should be no surprise to see fluid out the check plug on a cold pull. Then again, I don't see any benefit to pulling it ahead of the actual check procedure.
FWIW the 03-09 Haynes states a minimum of 115F for check temp which seems to be a recurring theme amongst those who have commented previously.