Transmission fluid change question

If it was easy with a filler, dipstick, and a drain plug kinda like an oil change, more owner wrench-heads would do it and dealers wouldn’t make what they do which I’m sure was somewhat on their minds when they designed it . Not everyone wants to bother to the level of caring for our vehicles like most of us do.

 

Some German cars don't have an engine oil dipstick. There is an electronic level check.

 

I didn't get that much or even close but let's say it's 1/4 quart difference. I wonder if even that would make any practical difference

 

The expansion should be dominated by the base oil. The worst case scenario would then be ignoring the dilution from additives, and pretending you've filled your transmission with just the base oil.
Picking a random API group 4 base oil from Exxon - this a full synthetic base oil, but I have no way of knowing if its one that actually gets used in ATF.
- https://www.exxonmobilchemical.com/en/chemicals/webapi/dps/v1/datasheets/150000000346/0/en
Specific gravity = 0.853; Density correction factor = 5.97x10^-4 (g/mL)/C
So for every degree Celsius increase of fluid temp, the density is reduced by that factor. That is,

SG * (1 - DCF*(Operating temperature - Standard temperature)

Standard temperature is 60 F or 15.56 C. Let's say operating temperature in the transmission is 220 F or 104.4 C. Then an initial SG of 0.853 becomes an operating SG of 0.808.

Since we're in SG, we can just multiply by the ratio of cold SG / hot SG, so your 3.5 quarts becomes 3.7 quarts. Someone else said a quarter of quart expansion, and this agrees. That 0.2 quart is ~ 190 mL, a little less than a red bull can.

 

Science is cool!
This sounds like we have a semi reliable data point. I believe the desired operating temp was 140-180 f if I remember correctly. You don't reach full temp for the level check. I changed my fluid on a warm day, say 80f. So that would make the difference smaller. I'll have to see if I can work through your math with those numbers to see if the volume difference i saw is closer than 190ml. I guess the question remains, how much fudge factor is there before you practically have too much fluid. Will seals blow at + 50mls?

 

I dunno

I’ve worked on aircraft for almost 40 years.
I don’t question engineers much
Follow the tech data and service as required, it’s much better than replacing components destroyed by improper maintenance

 

I agree with you but also disagree with you. Dealers can’t/won’t make much on transmission fluids changes when they tout it as lifetime fluid.

 

not sure i would use a sight glass on the underside of a vehicle. those kicked up rocks can find their way into anything

 

Sight glass with a screen protector? Don’t just give up…..come up with a solution.

 

Does the overflow not work? Seems pretty simple. fill the trans until you see fluid coming out of the overflow, bring to temp, open the overflow and wait for the stream to weaken before replacing the trans overflow bolt.

 

Sure. I’m just entertaining/supporting /encouraging ingenuity.

 

all i know is when it gets up to the recommended temp the temp gauge in the dash is at 1/4. good enough for me, i might be a teaspoon off!

 

I had a whole thing typed up about how you don't always want to do that bc engineers don't make all the final decisions, there could be other yadda yadda at play - and then I re-read the service manual (I only have a 2016 copy). I was going to say all this as an engineer myself - do question us, because sometimes it matters, and sometimes it doesn't, and we should have a good answer for you why if it does matter. Like on Monday I'm going to have a meeting where a key topic is whether a drain pipe is going to be sloped 1/8" per foot or 1/16" per foot. It doesn't matter, make it 3/32" or 9/64" whatever - it just has to free drain. But we have to clear it up so the piper can do her job and the civil works can finish theirs.

But faawrenchbndr is right to follow the manual here. The reason why you are repeating the drain and fill procedure with a warmup is because you are flushing old fluid out of all the different channels and parts of the transmission (like the torque converter), because it is an automatic and thus a hydraulic pump circuit. A "dry fill" of the automatic for the 2GR is 10.5 - 10.7 quarts (I think its around 13 if you actually replace the entire assembly and related subassemblies, but I can't find that number). The 3.3 quarts is a "drain and refill" only. So by repeating the procedure while warming up the trans and shifting, you're using the torque converter to pump new fluid through and push out old. This isn't a perfect drain and re-fill replacement, it's a flushing procedure.

1 - Drain and refill cold, flush via warming up and shifting from P to S and back. So 10.5 - 3.3 = 7.2 quarts old remaining
2 - Drain and refill warm, flush via warming up and shifting from P to S and back. So 7.2 - 3.3 * (7.2/10.5) = 4.9 quarts old remaining
3 - Drain and refill. So 4.9 - 3.3 * (4.9/10.5) = 3.35
There is now a little over 3 quarts of old fluid in there, if all the mixing was perfect. The adjustment factor in here is the dilution, this would be worse looking if you used the 13 or so for a total trans replacement. You could keep going to get more out, but on this last drain and refill, your ratio of old out : new in is less than 0.5, so diminishing returns has got you pretty bad at this point.

 

Real question, how far off would your level check be if your truck was for instance not 100% level, lets say 5 degrees tilted? Tilt the car a smidge and 200ml is negligable. Any of your math wizards capable of making a calculation?

200ml doesnt seem like much. Like I previously said, I overfill then run the car in idle for 5-10 minutes and then drain off excess. No check, recheck, risk of being too low, then jacking up truck again making sure its 100% level on both axis, and so forth. Always use same toyota fluid and drop pan. Only have done it 2x so far but not the depressing procedure it needs to be.

 

Why are you dropping the pan? The filter (actually not a filter, but a screen) does not need to be changed.

 

You can get more fluid out to change over by dropping the pan. Maybe an extra quart or two? Not sure of the amount. Whatever it is it allows you to freshen up more, an extra 10-20%, and while your there you can clean the pan and magnets.

 

If you drop the Pan and change the Filter you will be getting about half of the old fluid out - more is better.
You will also be able to clean the Magnets & Pan, as should be done.

The Filter is actually a Filter (not a Screen), and does need to be changed:
https://toyotaparts.mcgeorgetoyota.com/oem-parts/toyota-transmission-filter-3533004010

 

Dropping the pan only gets an additional 3-4oz
You do get to clean the sludge though, so that’s a plus

 

it’s actually a STRAINER….so more like a screen than a filter

 

I got an additional 2.5 QUARTS when I dropped my Pan and changed my Filter.