Do y'all recommend a transmission fluid flush?

[mripper]

I did the standard (lazy) drain and refill which seems to work well. I pulled the plug, drained about 4 quarts, then put 4 back in the refill. One thing I did notice is some small seepage around the pan gasket, probably because the new fluid filled above the gasket line with the engine off. However it's fine now, no more seepage once I drove the vehicle around and the new fluid was distributed back up into the tranny. If I see any issues, I'll do the fluid check procedure outlined in the repair manual (thanks for posting that btw)

 

[airforce1]

Kinda off topic but if there is a brief delay ~ 1 sec in engaging when reversing or getting into gear from PARK, it that normal?

Prior owner service record indicated a transmission flush was performed at 60 or 65K miles...mileage is currently at 67K.

 

[SWUtah]

View attachment 1394822
Well... yea, looks like they changed the severe service life with "Use AFT WS when recommended in owner's manual" There goes my fact argument, guess we are back to opinions and speculation men!

So Toyota also used to talk about severe and normal service. That was confusing for consumers, so they switched it to "if you tow."

Toyota used to describe severe primarily either towing or hauling, short trips (under 15 miles), driving on dusty or rough roads, driving in mountain regions, excessive braking, operating in temperatures under 32F or over 90F, and my favorite... driving at low speeds or long idle times (city driving to work).

Now, unless a user is driving in California temperatures, but on Nebraska open calm highways, never is stop and go traffic from work, and does not off road or have the weight of off road equipment, then I would agree he stays in normal service, but the vast majority of us live in the severe service level, or Toyota's towing level.

Back to towing, when I would tow a 7,000 lbs trailer on Florida highways, I didn't build any additional heat in the transmission. When I was unloaded, but driving head first into west Texas and Arizona wind, my trans temp was 50F higher the whole time because of drag. When i'm in Los Angeles traffic, I was at the same high trans temperatures. So while Toyota changed the words used, I don't see how the equipment changed with it.

In my '11 service manual on page 45 under 60,000 miles. It says if you Tow, replace the AFT fluid. That is the last thing I can find that references the TOYOTA WS severe service specs.

Great information and great suggestion

 

[pizdets17]

How does one drain 4 qts when the manual says less than 3?

I did the standard (lazy) drain and refill which seems to work well. I pulled the plug, drained about 4 quarts, then put 4 back in the refill. One thing I did notice is some small seepage around the pan gasket, probably because the new fluid filled above the gasket line with the engine off. However it's fine now, no more seepage once I drove the vehicle around and the new fluid was distributed back up into the tranny. If I see any issues, I'll do the fluid check procedure outlined in the repair manual (thanks for posting that btw)

 

[Arch Stanton]

I wonder if I put in 14 quarts a bit at a time how much of the original ATF I'm actually replacing. Anyone a wiz with hydrodynamics that can do the math?

I wouldn't be surprised if it was only 60%.

I've no background in fluid dynamics, but if we simplify things & assume that the draining process is unbiased (new and old fluid comes out in the same proportion as it exists in the transmission), the math is simple. You could in theory ensure unbiased draining by driving the car a few miles in between each drain/refill cycle.

The GX460 manual states that total ATF capacity is 11.1 liters, and drain & refill is done 3 liters at a time.

If you bought 12 liters, drained and refilled 3 liters at a time over n rounds, you would have replaced p=~71.6% of the fluid, with n=4 below:

p=1-(1-3/11.1)^n

If you want the number of 3-liter flushes to obtain p replacement, you will want to rewrite this as a function of p:

n=ln(1-p)/ln(1-3/11.1)

Now, if we want to replace p=0.95, or 95% of the fluid, we get:

ln(1-0.95)/ln(1-3/11.1)=9.507815

So yeah-- we would need to do 10 cycles of the 3 liter drain-refill step in order to replace 95%+ of the original fluid. That means it would take 30 liters of fluid to ensure you replaced 0.95*11.1=10.5 liters of fluid!

Not very efficient-- I think doing a mechanical flush is more cost effective.

 

[AnyMal]

I've no background in fluid dynamics, but if we simplify things & assume that the draining process is unbiased (new and old fluid comes out in the same proportion as it exists in the transmission), the math is simple. You could in theory ensure unbiased draining by driving the car a few miles in between each drain/refill cycle.

The GX460 manual states that total ATF capacity is 11.1 liters, and drain & refill is done 3 liters at a time.

If you bought 12 liters, drained and refilled 3 liters at a time over n rounds, you would have replaced p=~71.6% of the fluid, with n=4 below:



If you want the number of 3-liter flushes to obtain p replacement, you will want to rewrite this as a function of p:



Now, if we want to replace p=0.95, or 95% of the fluid, we get:


So yeah-- we would need to do 10 cycles of the 3 liter drain-refill step in order to replace 95%+ of the original fluid. That means it would take 30 liters of fluid to ensure you replaced 0.95*11.1=10.5 liters of fluid!

Not very efficient-- I think doing a mechanical flush is more cost effective.

I really needed to hear this today. Thanks!