ATF fluid route after pan drop...

[NightRiderQ45]

Guys, I have a quick question. I'm a electrical engineer by profession but it is driving me crazy since I'm trying to figure out how or where the new/old fluid goes after you add new after pan drop. Have I confused you yet lol??? Ok let me break it down into Layman's terms...

-after you drain the old fluid from the pan and put in the new atf fluid thru dipstick, it goes directly to the tranny pan right...so after you start your car and let it run for 5 min, does the new atf fluid go to the TC and old atf that was in TC go to the tranny pan???

The reason why I ask is because of the multiple drain/refill when changing atf. How do you know that you are not replacing new aft that's mixed with the old atf or each time you are doing the multiple drain, you're draining the old fluid?

 

[hate2work]

It mixes with the old ATF. When you do multiple drain and refills you are in fact draining out some new with the old, that's why many of us have gone to cooler line drain and refill which gets about 99% new fluid in there.

If you start early in the life of the tranny, regular pan drain and refills make sense.

OTOH, there are those that say doing a complete flush on an older, neglected tranny can do more harm than good.

 

[NightRiderQ45]

Thanks for the reply. That's what I thought. It's time for me to do a tranny fluid change. Last change was at 175k with M1 aft using the BG machine. I plan on using the machine again since it took like 15-20min max using this quick process. I think the main thing with the mechanical exchange is to make sure they purge their system before use.

 

[Trav]

My 2006 Infinity factory service manual specifies the line off fluid exchange procedure.
The main thing with machines is that they don't back flush the system,this can lead to possible transmission issues.Machines that use the transmissions pump to exchange the fluid in the normal direction of flow are fine.
I have no idea what type the BG machine is.

Amsoil and Mobil synthetic ATF works great with these units,any decent garage can perform the line off procedure using your fluid instead of possibly generic fluid with an additive to bring it up to specs.

 

[Craig in Canada]

Originally Posted By: hate2work

It mixes with the old ATF. When you do multiple drain and refills you are in fact draining out some new with the old, that's why many of us have gone to cooler line drain and refill which gets about 99% new fluid in there.


Well, that depends. I had some pretty interesting adventures trying to do a cooler line change with a BMW 540iA with the ZF AS440Z transmission. My best guess is that in P or N (the only two selections you in which you can start the car) they have a VERY high flow circuit from the pan to the cooler to the pan. It was like turning on a well-plumbed garden hose immediately after starting and it went red right away. This might make sense but it makes a cooler ATF change much, much harder.

D and R are still higher flow than "typical" DIY cooler line changers find, but at least it stayed brown and disgusting for a couple of seconds before going red.

In this case the "cooler" is actually a coolant/ATF heat exchanger, not an air/ATF loop in the rad.

Despite going to a lot of effort, and using 3.5-4 gal of Amsoil ATF ($$), we didn't get a nice, clean 99% change. The transmission acts completely differently though in a positive way, so mission accomplished I guess.

My message to the OP: As another electrical engineer, I'll tell you that the behaviour probably depends completely on the model of transmission in question. Other helpful BMW owners with the same vehicle chassis but a different transmission described a leisurely 15-20minute process of exchanging ATF where it would not flow at all in P and would lazily bloop out in D staying brown for a couple of gallons before fresh fluid finally came out. You may have to do some pretty specific research into your exact model of transmission to find your answers or make a friend at a transmission shop.

 

[Gary Allan]

On some domestic transmissions the cooler circuit is disabled in PARK. Some 80's Fords had some sleeve that covered over the ports in PARK. You can tell when the procedure calls for the level to be checked in NEUTRAL (or any selector position). That's pretty much been abandoned for obvious reasons. That's exclusive of any niche/nuanced flow path for the fluid in any specific mode. The fluid typically exits the convert through the cooler circuit since it's the location of the highest fluid temp.

 

[NightRiderQ45]

Originally Posted By: Trav
My 2006 Infinity factory service manual specifies the line off fluid exchange procedure.
The main thing with machines is that they don't back flush the system,this can lead to possible transmission issues.Machines that use the transmissions pump to exchange the fluid in the normal direction of flow are fine.
I have no idea what type the BG machine is.

Amsoil and Mobil synthetic ATF works great with these units,any decent garage can perform the line off procedure using your fluid instead of possibly generic fluid with an additive to bring it up to specs.

The BG machine does use the tranny own pump. Last time I used 15qts of M1 aft to do the exchange. I used syn atf because I figured that it would better fluid to deal with the heat of tranny.

 

[PT1]

The real issue is allowing electrical engineers to mess with a mechanical machine. Clearly a job for a BSME.

 

[Craig in Canada]

Originally Posted By: Gary Allan
You can tell when the procedure calls for the level to be checked in NEUTRAL (or any selector position). That's pretty much been abandoned for obvious reasons.


Every ZF transmission I've come across (which is admittedly only a few) calls for fluid level checks in P with the engine running, after going through all selector positions for a couple of minutes.

 

[Gary Allan]

As do many. The point was that some transmissions (not ONLY ZF owners will be viewing) disable the cooling circuit in some positions which would give you a false reading without it being energized.

 

[Craig in Canada]

Originally Posted By: Gary Allan
As do many. The point was that some transmissions (not ONLY ZF owners will be viewing) disable the cooling circuit in some positions which would give you a false reading without it being energized.


Yes, certainly. I was providing a data point and didn't mean to come off contradictory.

 

[NightRiderQ45]

Originally Posted By: PT1
The real issue is allowing electrical engineers to mess with a mechanical machine. Clearly a job for a BSME.

Hush lol! Remember, you need electric to run a motor...

 

[Gary Allan]

Quote:
Yes, certainly. I was providing a data point


..and one that I'll try and remember