Understanding the modern auto transmission

[displacedtexan]

I trust the opinions of the old guys working in transmission shops, and that’s cooler is better.

That's the same mindset that keeps people running 15w40 in modern diesels and destroying their valvetrain.

 

[SDHNTR]

It matters to me because I am an analytical person. I like to know the “why” of things. Especially things that go against conventional wisdom.

 

[SDHNTR]

I trust the opinions of the old guys working in transmission shops, and that’s cooler is better.

Right, and I previously thought I did too, hence this post.

 

[displacedtexan]

Fun fact, running a transmission below intended operating temperature is also hard on it. Wears it out faster.

 

[Fowl Play]

An engineer myself, but of course not a part of either team so can only make assumptions about the why. Each transmission cooler is sized to keep the specific fluid within a set temperature band so that it has the correct viscosity to lubricate the needed parts and seals. Toyotas typically use Dextron III or IV (not positive for 2024) while the Chevy likely uses the newer Dextron VI. Dextron VI is thinner so does not require as high of a temperature to hit that correct viscosity band. Toyota’s approach is likely “if it’s not broke, don’t fix it” so they haven’t redesigned anything to use the newer fluids — which have some benefits to lubricating faster at startup and fuel efficiency. As long as both are operating in the correct temperature band, they effectively do the same thing. Toyota just needs the higher temp as it has a thicker transmission fluid.