Are we over exaggerating the perfect ATF fluid level? thermal expansion seems to think we are

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May 27, 2023
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hello, i recently changed the atf fluid in my 2015 toyota. it has the u760 tranny and the u760/u660 have no dipstick so they have a certain level check that happens between 104f-113f and some docs say the fluid check can be done between 95-113f. The drain hole/port has a little fill tube preinstalled to do the fluid check. When the temp is around 104f, the instructions say to take out the drain plug and to drain and word for word based on the toyota document "Wait until the fluid flow slows and only drips come out"

depending on how much fluid comes out, a tranny could easily be at 115-120f when only drips come out. Also everyone has a different definition of 'only drips come out". I watched many youtube videos of people doing the fluid check and people were reinstalling the drain plug when the fluid was still draining as a slight stream, dribbling, and or dripping at a super slow speed. All in all it doesn't seem like anyone experienced any ill fate based on what they defined "a few drips come out" as

when i did my level check, idk how perfect i got it as i started dumping fluid out of the hole at around 104f and not sure what the temp was at when only a few drips came out. I probably reinstalled the plug within 30 seconds and when I did reinstall it, I was definetly closer to the "few drips coming out"

Of course I was planning to recheck the fluid in a few days which is why I didn't do a perfect level check the first time however all of this got me thinking.

I started wondering to myself on how much the fluid could even expand between the 104f to 113f and even if someone stopped the fluid level check at 120f how much extra fluid could even be drained/how 'off' the fluid level check could be. So I pulled up google and started looking for the thermal expansion of ATF which seems to be around 0.07% per delta degree celcius. So I decided to put some math into it and lets see what we come to. Just incase the 0.07% is too low, lets just round that value to 0.1% per delta degree celcius just so we can have the safest value incase 0.07 is not correct.

Toyota says the fluid level should be set at 104f to 113f. Which essentially means they give a 9F window to do the level check meaning even if you set it perfect right at 104F then that is the same as someone else who set it perfectly at 113F even tho both will have a slight variance in total fluid level in the system

Assuming most people probably reinstall the plug too late rather then too early (too much fluid is coming out and temperature heats up before plug can be installed)

For our example lets say a perfect fluid level check is at the average of 104f to 113F. so lets say the avg is 109F. Lets also assume 'Joe' ends up finishing the fluid level check procedure at 120F. (i seriously doubt someone could take longer then 1-2 minutes setting the fluid level as long as they started to take the plug out at around 100F. Lets also say the whole tranny and tubing/cooler line system holds a total of 10 quarts. (the tranny/tq converter holds about 6q from a dry fill so lets say 4q more for the cooler and the remaining tubing)

109F = 42.77 Celcius, 120F = 48.88 Celcius.
The delta of these two also known as the change in these two would be : 48.88C - 42.77C = 6.11 Celcius.

0.1% / 100 = 0.001 (to get rid of the percent). 0.001 / Degree C x 10 Quarts capacity x 6.11 C = 0.0611 quart expansion when starting at 109F and ending at 120F

Now lets expand that quart decimal and see what we get in ounces/Ml.

1 Quart is 946mL or 32 oz. Which means that 0.0611 quart is equal to 57.8mL or 1.96 oz

So essentially the fluid level in the whole system would only change by approx 2oz or 2 table spoons between 109F and 120F
which in other words means someone who set the level perfectly at 109F would have 2 tbsp/2oz more fluid then someone who incorrectly set it perfectly at 120F

Now this is where the discussion begins. I am not a tranny mechanic or a tranny engineer. But what I think is that there is no way that someone incorrectly setting the fluid level as described above could end up doing any damage to there tranny. 2 tbps or 2 oz is the smallest amount. Could a system that holds 10quarts of capacity really be bothered with a variance of 60mL? that seems like the tinyiest amount. HOWEVER i totally agree that someone setting the fluid level incorrectly and having 1quart under or 1 quart over is probably not doing there tranny a favor. I am in no way saying not to ignore your certain tranny fluid level check procedure. All I am trying to say is as long as you are in the ball park range of setting the fluid level on your tranny I doubt you can do any damage. I have spoken to many mechanics and alot of them just measure what came out and refill that much in and they seem to never have any problem and now that I got the math into it it totally makes sense. It seems like the only way people can do damage to there tranny or will have symptoms of wrong fluid level is if they are a considerable amount of fluid low or high. Maybe that value is a pint, maybe that value is 1 quart. I don't really know but I seriously doubt anything less then 100mL could do any damage.

I also believe that the reason these brands have a stingent fluid level check procedure is for the people who want it to be perfect and also so that most people are in the ballpark range. If they had no dipstick and no fluid level check procedure then people could easily be 1-2 quarts over or 1-2 quarts too less. So by following there fluid level check procedure, even if you don't finish it between there outlined temp range of 104f to 113F as long as you did it close enough to that temp range you are probably safe. I am not saying to do the fluid level check at 200F and assuming it will be the same as 104F, no way it will be. However as long as you finish the fluid level check at 120F or even 95F you are probably FINE since the variance between the perfect fluid level as per Toyota and being off by a few degree celcius / F can only really change the total fluid level in the system by maybe 1 tbps, 2 tbps, 3 tbps or 1oz, 2 oz, 3oz, etc


However I opened this thread as a discussion and hope to hear some knowledgable info about this, maybe I am completely wrong and that tranny's want there fluid level to be precise to the t and cannot tolerance a fluid level variance of 2 tablespoons but with just imaging a drain pan and thinking 2oz are gonna make or a break a tranny seems impossible for me to understand. If I am mistaken please let me know so this thread does not end up educating DIYer's or mechanics in the wrong way

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The whole system of checking the level through the drain plug came about because when people used dip sticks, the fluid temperature was all over the place when people checked and it was hard to get a consistent level reading. They were checking the level after a drive around the block one day and a half hour on the highway the next. This now standardizes it at a specific temperature range that most owners and shops can reach in a few minutes of idling. 2 ounces more or less wont cause any issues.
 
The whole system of checking the level through the drain plug came about because when people used dip sticks, the fluid temperature was all over the place when people checked and it was hard to get a consistent level reading. They were checking the level after a drive around the block one day and a half hour on the highway the next. This now standardizes it at a specific temperature range that most owners and shops can reach in a few minutes of idling. 2 ounces more or less wont cause any issues.
exactly! now i understand why there isn't a dipstick anymore. seems that as long as you are 'close enough' you are good to go
 
where did you come up with the expansion coefficient from?
I think atf is abit higher.

also that is the acceptable range. Doing it at 32f vs 100f would net a more significant number.
ie my new fluid was stored in the garage.
 
where did you come up with the expansion coefficient from?
I think atf is abit higher.

also that is the acceptable range. Doing it at 32f vs 100f would net a more significant number.
ie my new fluid was stored in the garage.
I just found this on google but not from a proper book, would love for someone to chime in if they have the number
regardless if someone is bored and can put some atf in a graduated cylinder and set it to like 5ml and then heat that cylinder to 120F we would have a decent idea of how much it expands

"The thermal expansion range for various petroleum products seems to be between 0.0007 and 0.001. " this is already in decimal form which is why I chose the higher value of 0.001 as my calculation decimal.
 
Last weekend I changed the ATF in my 2021 Traverse. To plan, I had put the new ATF in the garage so it would be the same temp as the fluid in the trans. My Wife drove the car on about a 5 mile round trip, as I didn’t tell her to use another vehicle. I did the fluid drain anyway and measured the fluid at 5 quarts, 26 ounces. Guess what, after cooling down to for 24 hours (to roughly 60 degrees) it was still 5 quarts, 26 ounces.
 
There is more error introduced by how close to perfectly level is the car front to rear, left to right in the setting of ATF fill. The OEM assy floor is level, but they use specialized metered machines to fill the transmission regardless of attitude of the car. OEM's won't tolerate 80ml of extra added to any vehicle for any fluid because of the $$ loss that represents.

Most DIYs don't achieve perfectly level car but the risk is not great and if you fill the transmission / engine / differential / transfer case and use 5% more than OEM...it's only affecting your pocket.
 
Ok, I only read the first ~3 paragraphs of Post #1 but if I understand the gist I 100% agree. People get off on acting like this is a VERY PRECISE science but I also started a thread on the Tundra transmissions because there is plenty of conflicting info on the web about the proper temp. And personally I'd say 100 vs 130F is a HUGE difference when you think about it (yes, yes, 30%)

In the end, I don't think it really matters that much. To be clear, I'll still follow the "proper" procedure but to some extent it's security theater ‐‐ like 😷 between bites.....
 
Ok, I only read the first ~3 paragraphs of Post #1 but if I understand the gist I 100% agree. People get off on acting like this is a VERY PRECISE science but I also started a thread on the Tundra transmissions because there is plenty of conflicting info on the web about the proper temp. And personally I'd say 100 vs 130F is a HUGE difference when you think about it (yes, yes, 30%)

In the end, I don't think it really matters that much. To be clear, I'll still follow the "proper" procedure but to some extent it's security theater ‐‐ like 😷 between bites.....

ahaha all good i understand it is a long read however just some food for thought the remaining paragraphs outlined how in your situation i do agree 30% of temp increase looks like alot indeed however on a fluid expansion basis the diff in fluid level between those two temps with calculations and assuming 10q capacity of the whole system would be approx: 5 oz ish or 160mL

however if you did it at around 115F then the variance between doing it at 100f or 130f would be around 75mL which is 2.5 ish oz

which doesn't seem like much considering how you look at it
 
The exact level is obviously important.
This is how Toyota suggest you check it :

In my opinion, start draining as soon as the temperature range is reached and finish draining by the time the upper range is reached would give you the near perfect desired level. Best achieved by getting as get as close as possible to the correct level to star with.
 
The exact level is obviously important.
This is how Toyota suggest you check it :

In my opinion, start draining as soon as the temperature range is reached and finish draining by the time the upper range is reached would give you the near perfect desired level. Best achieved by getting as get as close as possible to the correct level to star with.

i totally agree that would be perfect but what i was outlining above in the ppst is even if you miss the perfect range by a little bit due to either pulling plug too early or draining for too long which resulted in passing the upper temp range, the thermal expansion of fluid shouldn't be more then 60mL considering a whole 10 quart system which is very neglegible in my opinion
 
Last weekend I changed the ATF in my 2021 Traverse. To plan, I had put the new ATF in the garage so it would be the same temp as the fluid in the trans. My Wife drove the car on about a 5 mile round trip, as I didn’t tell her to use another vehicle. I did the fluid drain anyway and measured the fluid at 5 quarts, 26 ounces. Guess what, after cooling down to for 24 hours (to roughly 60 degrees) it was still 5 quarts, 26 ounces.
wow definetly food for thought, could mean that the thermal expansion coeffiecint could be lower then what i used for calculations above
 
A Toyota tech on this board told me they do it by measuring what came out. I plan on weighing mine when I get around to it.
That's interesting 'cause Car Care Nut has said not to do that.

I will admit, if you're positive you can catch ~98% of what came out and accurately measure it AND all other things are equal (like the temp of old fluid and new fluid), it's difficult to see how that won't work fine.

How is looking at the level of drained fluid in a graduated bucket different than reading lines on a dipstick after all? But again, I'll continue to do the "proper" procedure because it's OBVIOUSLY VERY important and the transmission will absolutely explode whilst of course taking down the obligatory bus load of nuns.

The key is deciding which is the "proper" procedure :D Do you identify as the lower temp range human or the upper temp range human? Or perhaps non-binary and it changes each day??
 
i totally agree that would be perfect but what i was outlining above in the ppst is even if you miss the perfect range by a little bit due to either pulling plug too early or draining for too long which resulted in passing the upper temp range, the thermal expansion of fluid shouldn't be more then 60mL considering a whole 10 quart system which is very neglegible in my opinion
I "played around" with the dipstick level in a 2004 Volvo XC 70 and estimated the range between maximum and minimum was less than 100 mls.
 
...meaning the correct level is critical unlike engine oil
But agree with everyone. I do not think anyone who is on this discussion, by the very nature of it, would get the level outside of a safe range.
 
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I "played around" with the dipstick level in a 2004 Volvo XC 70 and estimated the range between maximum and minimum was less than 100 mls.
I’ve come up with closer to 200ml between min and max on the same transmission. Either way, we are both saying the same thing - a couple ml makes a difference.

So does temperature on that transmission. 20C and 80C ranges are a solid 2-3 cm apart. Huge variation in fluid level depending on temperature. Much great than the OP’s math would suggest. Which calls into question both the math, and the assumption set that was made when doing the math.

The factory gave us a way to check/set the level. Whether it is a Toyota, Volvo, Mercedes, or whatever.

I really don’t see the point in deciding, via specious arithmetic, that the procedure does not matter. I will trust the factory procedure over the arithmetic of a guy I don’t know, who is not a powertrain engineer, and has only once changed the fluid on his Toyota.
 
The transmission on my car has a dipstick, it's 4mm overfull after a 30m highway drive. No ill effects.

The stick has letters stamped on it that say do not overfill
 
I’ve come up with closer to 200ml between min and max on the same transmission. Either way, we are both saying the same thing - a couple ml makes a difference.

So does temperature on that transmission. 20C and 80C ranges are a solid 2-3 cm apart. Huge variation in fluid level depending on temperature. Much great than the OP’s math would suggest. Which calls into question both the math, and the assumption set that was made when doing the math.

The factory gave us a way to check/set the level. Whether it is a Toyota, Volvo, Mercedes, or whatever.

I really don’t see the point in deciding, via specious arithmetic, that the procedure does not matter. I will trust the factory procedure over the arithmetic of a guy I don’t know, who is not a powertrain engineer, and has only once changed the fluid on his Toyota.
my apologies if my original post was unclear. I believe there is a misunderstanding on what the moral/tldr of my post was

I don't mean to say for people to disregard any level checks. I am just saying how if someone is doing a level check on a toyota that has the level check procedure similar to mine, then even if they complete the level check a few fahrenheit too early or too late, it will make a negligible difference on the tranny fluid level.

In other words if a dipstick says to check the fluid level at 120F, however you ended up checking it at 115f or 125F it does not matter as long as you tried your best to check it close to 120F. checking the level at 200F would be a completely different story

Of course if we do my same calculation between 20c and 80c, even the math that i stated above would show a way greater variance of fluid (20c-80c would be almost half a quart of fluid expansion with a rough estimate).

just to clear any confusion, i do not mean or intend to mean for people to throw out the level check at all or be checking tranny levels's ice cold when they are supposed to be done piping hot.

I am just saying if you try your best and do the fluid check at close enough to the book's temperature, you will definitely be fine
 
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