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I would just like to see one link to any of these claims of Toyo Truck Trans Sealed relevance by Manufacturer, ie Aisin.
Motor Oil is MUCH more Hygroscopic than Tranny Fluid and last much much longer by just that fact.
Tundras 2004 & earlier with Tranny Fluid Dipstick are what is considered an example of Nonsealed Automatic Transmissions, correct?
Bunches of those still run ing great well past 250K having had no Fluid Exchanges, I do believe.
Tossing equations is all well & fine Professor, but a source verifying theorems and calculations specific to an actual effect affecting WS OEM or earlier requirements fluids would certainly settle the case better.
Until then, making popcorn!
 

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The air space in the transmission really regulates the pressure and allows for expansion and contraction of the fluid. And while the fluid does expand some, the transmission case also grows with temperature and offsets some of that expansion.

To calculate the air space pressure, you can use the equation pv=nRT to calculate the pressure created in the transmission from the change in temperature. V is volume and stays constant and n and R are fluid properties and so they stay constant as well. When you solve the equations, all the constants cancel out and you are left with p1(T2)/T1 = p2. T and p are in absolute units, and if we assume the final temperature is about 200F, you end up with 14.7(200+460)/(70+460) = p2 = 18.3 psia, or 3.6 psig.

If you assume the volume of air is reduced by 33% because of the fluid expansion, then you would multiply p2 by V1/V2 or 1.5/1, and the pressure would be 5.4 psig.

You can play around with the numbers and see what the pressure would be if the temperature was 300 instead of 200, or if the air space volume were reduced by 50% instead of 33%, but no matter what you do, the pressure is not very much and is easy for the transmission seals to handle.
Yeah! What he said!!! 馃お
 

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Sealed transmissions are like sealed differentials and transfer cases.

Figments of Imagination.

Sealed mayonnaise is real however.
 
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OK. For those who want to learn, here we go.

Here is a link to the patent for a sealed transmission breather. This will explain why a sealed transmission has a breather and how it prevents or minimizes oxidation of the transmission fluid. US5129422A - Transmission breather control valve - Google Patents

Here is one from the society of automotive engineers (SAE) also about breathers on sealed transmissions, and although you have to pay to read this one, you can read the summary and get the idea of what they are talking about. Transmission Air Breathing Suppressor (TABS) Valve - A Device for Improving Automatic Transmission Fluid Life

Here are a series of 5 history of transmission fluid videos done by Prof John Kelly who is the most knowledgeable transmission nerd I know of. In part 4 of the history of Chrysler Trans Fluid he talks about the discovery of sealed transmission fluid longevity and explains why preventing people from checking the fluid and adding fluid and exposure to oxygen are all bad and led manufactures to eliminate anyone being able to check or change fluid easily. He talks about doing a lifetime fluid video, but it does not look like he every finished it. If anyone can find it, drop a link because I would love to watch that.

This is a good article that has a section that talks about lifetime fluids. It has a good history of transmission fluid and talks about the original discovery of hermetically sealing fluid in the transmission by Chrysler . https://everipedia.org/wiki/lang_en/Automatic_transmission_fluid

A couple more things:

I don't care one way or the other if you change your transmission fluid. I can only explain the engineering behind why manufactures are saying that under normal driving conditions you don't have to do that. You do what makes you feel good.

I am not going to explain the math. It's Jr high school level chemistry and algebra.

Last:

For those who want to argue against Toyota's recommendation to not change the trans fluid, I ask what is Toyota's motivation? Are they trying to boost their 15 year/300,000 miles transmission sales? Why would they want to sell less transmission fluid and why would the dealers want to do less maintenance work? And why would they want to purposefully shorten the life expectancy of their trucks over transmission fluid?

I think the answer is that they think their transmissions on average will last 3-400K miles without any service, and even when the transmissions does fail, it will probably not be because of the fluid. And that happens to be my definition of lifetime as well, so I don't plan to do anything more than a pan drop and filter change every 125-150K.

The best of the best to ya all!
 

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OK. For those who want to learn, here we go.

Here is a link to the patent for a sealed transmission breather. This will explain why a sealed transmission has a breather and how it prevents or minimizes oxidation of the transmission fluid. US5129422A - Transmission breather control valve - Google Patents

Here is one from the society of automotive engineers (SAE) also about breathers on sealed transmissions, and although you have to pay to read this one, you can read the summary and get the idea of what they are talking about. Transmission Air Breathing Suppressor (TABS) Valve - A Device for Improving Automatic Transmission Fluid Life

Here are a series of 5 history of transmission fluid videos done by Prof John Kelly who is the most knowledgeable transmission nerd I know of. In part 4 of the history of Chrysler Trans Fluid he talks about the discovery of sealed transmission fluid longevity and explains why preventing people from checking the fluid and adding fluid and exposure to oxygen are all bad and led manufactures to eliminate anyone being able to check or change fluid easily. He talks about doing a lifetime fluid video, but it does not look like he every finished it. If anyone can find it, drop a link because I would love to watch that.

This is a good article that has a section that talks about lifetime fluids. It has a good history of transmission fluid and talks about the original discovery of hermetically sealing fluid in the transmission by Chrysler . https://everipedia.org/wiki/lang_en/Automatic_transmission_fluid

A couple more things:

I don't care one way or the other if you change your transmission fluid. I can only explain the engineering behind why manufactures are saying that under normal driving conditions you don't have to do that. You do what makes you feel good.

I am not going to explain the math. It's Jr high school level chemistry and algebra.

Last:

For those who want to argue against Toyota's recommendation to not change the trans fluid, I ask what is Toyota's motivation? Are they trying to boost their 15 year/300,000 miles transmission sales? Why would they want to sell less transmission fluid and why would the dealers want to do less maintenance work? And why would they want to purposefully shorten the life expectancy of their trucks over transmission fluid?

I think the answer is that they think their transmissions on average will last 3-400K miles without any service, and even when the transmissions does fail, it will probably not be because of the fluid. And that happens to be my definition of lifetime as well, so I don't plan to do anything more than a pan drop and filter change every 125-150K.

The best of the best to ya all!

Thank you!
Exactly and understandable for my addled brain, and like you, We can only share, not any stake in anybody else's choices, trucks or business.
Carry on, my Tundra Fam.
Keep On Truckin
 

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I really wish it was a filter.
It is really an ultrafine screen though!
As with most of my maintenance and rebuild items, I purchased mine from Toyota long ago.
Didn't see the Pando and Disability on the betting form, so have really reduced the use of my Girl greatly.
But when the time comes I'm stocked up!

After watching that YT on Toyota fluids, I am now afraid to use the 2 gallons of Valvoline WS Compatible to do my upcoming D/F.
No issues caused using it posted/stated by others.
And it's what I have. Guess I'll risk on one D/F and full replace if any new strangeness occurs.
Can't go wrong using Toyota WS like my 1st D/Fs using over Gallon and a half.

The next batch of Popcorn is in the microwave now!
 

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OK. For those who want to learn, here we go... [snip]
... you have to pay to read this one, you can read the summary and get the idea of what they are talking about. Transmission Air Breathing Suppressor (TABS) Valve - A Device for Improving Automatic Transmission Fluid Life
Thanks for the nice summary & info!
Here is the full text of the SAE paper:
 

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... After watching that YT on Toyota fluids, I am now afraid to use the 2 gallons of Valvoline WS Compatible to do my upcoming D/F. ...
There's much indirect evidence that Toyota's trans fluid is manufactured by AISIN Corp : AISIN Part# ATF-0WS.
Aisin is major manufacturer of auto components. Aisin has supplied transmissions to Toyota, including the newest 3rd-gen Tundra.
Aisin fluid is about 1/2 the list price of Toyota fluid ... right now, Aisin is about $7.40/qt at RockAuto, one of the lower prices around. (was only $5.80 few yrs ago).
Also, Aisin's USA operations are partly owned by Toyota.
 
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