Tranny fluid flow direction

[Roger]

Which way does transmission fluid flow when you flush? Fill tube to pan to torque converter to radiator? Or is it fill tube to converter to pan to radiator? Or is it ?????

I'm basically wondering if I drain the pan 1st, refil and then disconnect the return line from the radiator, is new fluid pushing out old? or is it mixing and pushing out new with the old?

Does my question(s) make any sense?

[ October 17, 2003, 10:43 PM: Message edited by: Roger ]

 

[MolaKule]

The return line from the radiator back to the transmission is the one which should get the new fluid (lower pressure "suck" line). Old fluid would come out of the radiator to the waste oil bottle.

I don't know what vehicle you have, but on all of my vehicles, the top line is the higher pressure line coming from the tranny (hot fluid), and the lower line (cooler oil, lower pressure) goes back to the tranny.

If you identify your vehicle and transmission, some of the more experienced technicians or mechanics here might be able to clarify which line is which for your vehicle.

 

[instigator]

some vehicles dont have a "suction line" the return lines are nothing more than a tube running to the pan to dump the cooled fluid. both my toyotas are this way so in order for you to do the flush like i think youre talking about, you'll just have to run the hose from the tranny to a graduated bucket and start your engine for just a few seconds and replenish the fluid the same amount that has been dumped into the bucket.
finding the line you need is going to be the trick. usually the one tube from the tranny thats higher that the other (on the tranny) is your pressure to the cooler line the other would be your return to pan line (at least on my cars)
also plane on about 12-15 qts for the flush, just do the cylcle untill fresh fluid is coming out of the line

 

[Roger]

quote:

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The return line from the radiator back to the transmission is the one which should get the new fluid (lower pressure "suck" line). Old fluid would come out of the radiator to the waste oil bottle.

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I'm obviously misreading your answer. How can the old fluid come out the line that gets the new fluid?

I have 2 Nissans and have changed the fluid in both previously by 1st draining the pan, refilling new fluid with the same amount that came out the pan, and finishing the job by disconnecting the radiator return line to get the balance. But I can never tell when all the old fluid is totally expelled. The color change is never that obvious to me. So I always wonder if I stopped too soon and didn't get all the old fluid out. If the new that I add before disconnecting the radiator line "pushes the old" ahead of it, I'm okay. I just don't undestand the tranny's internal plumbing route well enough to be comfortable with what I'm doing. Thanks.

 

[MolaKule]

The high pressure line (hot fluid) from the tranny usually goes to the top of the radiator (internal) cooler tank (an internal heat exhanger in the radiator). The bottom line (lower pressure) but cooler fluid returns to the transmission. This is where you make the break. Remove this line and place hose (or extend hose) into new fluid bottle since this is where suction will take place.

The connection from the radiator tank will then dump old fluid into the waste oil bottle. You may need another extended hose for this connection with a hose clamp since pressure will blow it off if you don't clamp it.


I prefer to remove drain plug, simply drain old fluid, replace drain plug, and then pour required amount of fluid into tranny and check level while tranny and engine are hot.

Run a week or so and then repeat process until fluid appears red and smells fresh like the new fluid. With most Nissans, this is a piece of cake.

[ October 19, 2003, 12:17 AM: Message edited by: MolaKule ]

 

[Ken2]

In most transmissions there is more ATF in the torque converter than in the pan, and it doesn't drain...thus the reason for flushing through the cooling lines.

To find the direction of flow in the cooling lines, disconnect one line, put drip pans under both open ends, disable the engine so it won't run, and crank it. You'll see the flow.

Hondas and some other transmissions have a small enough volume that a triple pan drain does a good job of changing the ATF...drain, refill, drive, and repeat twice more.


Ken