2020 Transmission Drain and Fill

What would be absolute worst case scenario if all I did for my 15’ transmission drain it ambient temp then pump the same amount back in? Also sitting at 130k with a very good likelihood of only having one trans fluid change (bought it at 100k)

is it absolutely necessary to get to temp then check the level?

 

I'll get chastised for this, but, here goes: (assuming you do not have a trans temp monitor)

just warm up the engine for 5 minutes. then check the level.


I'm sure the Toyota engineers will jump in here & tell you to wait for the exact 105* or whatever.....but the difference in thermodynamic expansion between 80* & 120* is so small, it's laughable.


for theatre of the mind...I add about a quart more than came out...and then use the check valve to perfect the level.


and, no. I will not define a trickle.

 

On your first I wouldn’t replace exactly what you drain. When I drained and filled recently I found it was a little under filled from the factory.

 

Sage words.



overfill it about a qt & then do check valve thing.

 

That’s what is kinda funny about the process. Very specific conditions under which to initiate the level check, but the level check itself is a “trickle”.

A few on this forum have drained very warm fluid, and when it cooled to ambient temp, the difference was barely noticeable if at all.

 

It’s best to do it correctly and not as hard as ppl make it out to be; I think you’ll be surprised how straightforward it is. For reasons already stated though, my take is it’s better to have fresh fluid than perfect levels. It’s not very sensitive to thermal expansion and the trans isn’t very sensitive to the fluid level. Three 2.5 gens I’ve done were all ~3/4 quart overfilled from the factory. (Made me doubt my process on the second one so repeated it all….)

TLDR: use the “return what you took out” method is OK.

 

I’ve read on here a few times that 2019-2021 trucks were overfilled, possibly for the transmission cooler that isn’t there.

 

What’s the biggest down side to being overfilled? More fluid resistance in the tranny?

 

After pumping fluid into the tranmission, I start the truck and drain from the check plug to whatever the subjective definition of a trickle is. Waiting to get to the temp range is damn near unnecessary. Better to have the fluid a little colder than specified range than to overheat it and restart the process.

I'm sure there is a decent tolerance in terms of correct level. Being toyota, I wouldn't be surprised if it's +/- .5 qt.

 

Also somewhere it says the air temperature can't be above 80 degrees. Pretty hard to do summertime in Florida.

 

You’re probably right. Ain’t no way this fluid level needs to be accurate to the degree some folks are making it out to be. I’m not suggesting that you get it within the nearest gallon, but a half quart seems very plausible for a margin.

If it were that critical, think how many transmissions would be blowed up by going up or down a hill. Or around a corner…

I’m no rocket surgeon, but it’s just a big pan with go-juice in it.

 

Lmao…rocket surgeon. I’ll be working that into conversations from now on.

 

Yeah, it ain’t rocket surgery.
Longtime personal favorite, for sure.

Right up there with “It may not be very big around, but it sure is short.”

Or, “What could go wrong, if we’re smart about it?”

 

I mean if you wouldn't check the dip stick either then i guess it wouldn't matter but the check procedure isn't much harder than checking a dip stick. Once you do the check procedure once you'll be like wow, why have i been fighting doing this, it's simple. The difference between a stream and trickle is pretty easy to see when you do it as well.

 

No one is saying fill it and dont check it. All that's being said is that the acceptable level isn't that complicated. These transmissions are very easy to deal with. As long as you're in the ballpark in terms of fluid level, you're good to go. Theres people who literally just replace the amount of fluid that they drained and never crack open the check plug and theres no reports of those transmissions breaking down lol

 

I understand that because I also and somebody who at first just did the drain out and replace what came out method and then I realized how easy it is to just do it correcty. If you're going to crack open the check plug why not do it at the correct temperature? There's even a built-in method you can do with the shifter to know the correct temperature to open it at if you don't feel like buying an OBD tool.

 

@Joe333x - I am not addressing you directly...just using your post.



Nobody asked me, but here goes:

doing the check level, without temp check, procedure gets you >95% accurate.

it's not that important to check the temp.

yes, it's easy to check temp.

but, it's not really necessary if you simply warm the engine for...say...5 minutes*.

and if you lack the ability to check the temp, just warm up the engine and now you are >99% accurate.


sidebar...don't get all balled up over being under temp and then....not get balled up being over temp.
you have about 3 minutes to check the level when the truck is running - to meet the temperature window.



*I say this because EVERY time I've D&F'd, it took about 5 minutes to get to temp. so now I don't even check the temp.

 

I'm confident in my method because by the time im done draining through the check plug, my scangauge tells me im within toyota's specified temp range anyway. Like another person said, it doesn't take that long to wait to be 99% correct, but damn, I don't have a lift and getting under the truck while its running and the cat is hot is not fun for me anymore.

 

<read this in a happy tone - as I laughed when I thought of it>


and for you guys that don't do the transmission fluid check level procedure-

are y'all the same guys that change your oil & don't check the dipstick?

because it's the EXACT same thing.

 

I check the temp because.......I like following procedures when it comes to vehicles .

However, given the fact that the procedure involves the highly subjective "trickle", I don't think it is that sensitive to over or under filling, to the point that if the procedure weren't followed and you just replaced what was drained, that you'd probably be totally fine.

Where I think the procedure helps the most is if you add a cooler and then you actually need more fluid, affecting your baseline.

Or, when you are an idiot like me and accidently knock over your drain pan and don't know how much you actually drained out.

 

Technically no one lacks the ability to check the temperature since you can follow the shifter method that will flash at the correct temperature.

 

Please expound on the shifter method

 

Check out this video about 8 min in for a good description:
https://www.youtube.com/embed/NUAuGmDGntY

 

Only because I know people are lazy, here's a link to bring you right to the procedure.
https://youtu.be/NUAuGmDGntY?t=345

Here is a post from someone with a 2020 that I guess is missing the pin in the OBD that you need to jump
https://www.tundras.com/threads/tra...jumper-on-a-2020-trd-pro.126414/#post-3333227

Apparently newer ones do not even need the jumper wire
https://youtu.be/XTU_Jt7OJZk

 

So I decided to drain and fill my tranny this past week on my 2020. I felt like it was under filled as it was always a little rougher shifting when cold. Drained out just a hair under 4 quarts and added 5. Used the check valve once it hit 99 degrees and let it get to a point where the stream started to wave a bit right about the 40:02 mark of the video on post #7. Maybe just a bit longer than that. After measuring what I drained out from the check valve it was right around a half a qt. Seems to shift well and it’s summer now so can’t really judge the shifting in the cold, did I not let it drain enough or is it possible I was about 1/2 qt low?

 

https://youtu.be/XTU_Jt7OJZk?si=blQRAfNWM_r_TTRR

FYI to everyone - This temperature check mode method works on my 2021 tundra. Using a jumper wire on the OBD did not work for me.

Edit - Just saw that someone else also posted this.

 

My first test drive after changing mine i was about 3/4 quart low and noticed rough downshifts. once i figured out the temp check mode later that day, topped her off and she was golden. Shifting a tiny tiny bit rough when cold is normal though, you could just be hyper analyzing it.

 

Yeah that’s kind of my thing. I’m a little OCD at times and I did double check my level and it was all good.

 

After reading the procedures and watching the videos, I’m still left with 1 question in regards to doing this fluid swap. When it says to make sure the truck is level, should I be checking the frame or the ATF pan? Does it matter??

I have a Bilstein 5100 lift (top setting) with 1” shackles in the rear so I’m about 1.25” higher in the front than stock.

I have a scan tool and am able to monitor ATF temps, so this is the only thing that I’m not 100% sure on.

 

Doesn't matter too much. I jist get the truck on a flat surface and go from there. If you want to get more precise, get the pan level.