Looking For The Truth Re ATF Level

Looking for opinions on what a local tech told me about checking ATF level on my 2nd Gen Tacoma.

So, I tell him he needs to check the level at the correct temp. using a scan-tool to monitor Transmission temperature...
He tells me he's got all the certifications and he knows better. He asks me why check at the correct temp? I said, well every transmission I've ever had needed to be checked while hot; I assume the fluid expands with heat.

He tells me, fluid doesn't expand with heat. He says the reason for checking while hot is so the fluid will be distributed through the transmission and especially the torque converter.

Opinions?

 

Sounds good to me

 

I think you know the answer. The tech is lazy and incorrect.

 

It is my understanding that the temp range is a guidline of time and not neccesarily temprature. From cold to the "fluid temp check range" is enough time for all the fluid in the sump to fill all the lines, trans cooler( if you have one ), valve body and the TC.

These respective parts of the trans need to be full of fluid before your drain the excess. And yes warm fluid does help with viscocity and fluid movement. Ie. Easier to drain in super cold temps.

 

The thing is. After doing my homework and watching several videos, I had the impression that when hot, the level rises due to fluid expansion.
However, that is completely opposite from the "distribution" theory because when distributed through the transmission, the level would do down.

So, which theory is correct? "Expansion Theory" or "Distribution Theory"???

 

Distribution.

 

All transmissions have a specified temperature to check the fluid level, that is because fluid expands and contracts with temperature.

The A750 specified temperature is 95-115F, if you don't check it in this temperature range the level won't be correct.

 

Think about where the check plug is located -down low or near the top. And then think what happens when you pull the plug when the trans is cold - does it spurt out or is it no where near the level? And then think about how much fluid you get when you pull the drain versus how much is retained elsewhere in the transmission.

I'm no expert on transmissions, but as a lab dude that spends a lot of time with non-aqueous fluids, I can tell you that most do expand by a large factor with temperature. And I've drained the trans both cold and hot. Other than it threatening to melt my bucket a near equal amount drained independent of temperature, and both times it was between 25-30% of the total capacity.



It's thermal.

 

found your problem. anyone "that knows better" is not someone worth being associated with, by either distance or tangentially.