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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Do you identify as the lower temp range human or the upper temp range human? Or perhaps non-binary and it changes each day??
