In what ways is ATF different from engine/gear oil

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How exactly is an ATF different from a typical engine or gear oil ?
I realize its something do with pressure and hydraulics v/s friction. Is it supposed to be a "double duty" oil ? i.e. gear oil and hydrualic fluid in one ?

What function properties/characteristics are more desireable in an ATF as compared to oil ? Asked another way - What is most detrimental to an ATF - pressure ? heat ? friction ?

One more question -

Even though the transmission fluid is subject to the same kind of temperature variations as engine oil, i.e. very cold starting temps in winter to normal operating temp in summer. So why isn't grade range specified in an ATF ? Unless all kinds of ATFs fall in more or less the same grade ?
 
Friction modifier, it's about the same as 20 weight oil for viscosity typically, and it has different additives as anti-oxidants and detergents.
 
Oh wow. They are very different. The real big one is friction characteristics.
The main concerns are heat and contamination.
In earlier days the primary failure mode used to be bulk oil oxidation wheras these days it is degradation of the friction package that is the main concern.
 
Originally Posted By: Pablo
I can pretty much agree with that 100%, although there are still some fluids out there with base fluid degradation as well.


For sure. When I made the statement I was thinking about good modern ATFs. In fact many of the fluids that now claim to meet the old DEXRON-III performance would not meet III(H) and from what I have seen maybe not even III-(G). If you test them some are quite shocking, which is one of the reasons that you see me continually harping on about using licensed products
 
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