Questions about the process(es) of changing automatic transmission fluid

Messages
9,597
Location
Virginia
"I am sure we don't know how a auto trans lube and torque converter and control oil circuits work" Quote means not a negative on Clineberger's obvious skills ! but as a [we ] in the multitude of posts on this subject , do not know how the hydraulics of a trans works.


What ct8 is saying....

Is "we" aka the 99.999 percent of us champions on here.... Don't know how that system really works.

That aka "we" did not include Cline... Or Trav or The Critic...
 
Messages
2,837
Location
Caldwell Idaho
I have posted this before and here goes again . We are lucky to have the industry processionals aboard from the auto industry . the oil industry , The aviation sector and the vast amount of others that help us out with our problems. The expertise is obvious.
 
Messages
9,597
Location
Virginia
I have posted this before and here goes again . We are lucky to have the industry processionals aboard from the auto industry . the oil industry , The aviation sector and the vast amount of others that help us out with our problems. The expertise is obvious.

^^^^^^^^^^^^^^^^
I agree one thousand percent....
 
Messages
7,456
Location
Los Gatos, CA
I have posted this before and here goes again . We are lucky to have the industry processionals aboard from the auto industry . the oil industry , The aviation sector and the vast amount of others that help us out with our problems. The expertise is obvious.
I think I misunderstood your earlier post. Apologies.
 
Messages
339
Location
Independence Ky
In my case my van has a drain plug on the torque converter. Is it ok to drain it and the pan? Then add the same amount back? My concern is starving the pump being this would probably be at least 9 quarts or so drained out of the transmission. 1994 Ford E150 5.8L E4OD. I know I’ve heard of others doing this but I just worry about starving the pump.
 

Lumberg

Thread starter
Messages
494
Location
Washington DC area
I think if the torque converter is literally designed to be drained that it's OK to drain it and the pan, then refill the pan with the same amount of fluid, and fire it up.
 
Messages
1,806
Location
TX, USA
We've all seen the threads debating what kind of ATF to use. Can we talk about how to change it? As far as I can tell, there are at least two methods:

  1. Multiple partial drain/refills: the most common DIY method where you drain about a third of the transmission at a time, top it up, start the car and run through the gears, rinse and repeat twice.
  2. A flush machine: this is a machine with a pump in it which connects to the lines leading from the transmission to the radiator. This machine essentially replaces the radiator in the loop and receives dirty fluid from the transmission and sends back fresh fluid from a pre-loaded resevoir. I'm told that these aren't the safest and can "bend fins inside the torque converter", Is this bro science? For the record, I have a Toyota 86 with a variant of the AISIN A960E.
  3. ???? I think I have seen people referring to a process that is DIY but also somehow uses the lines between the transmission and the radiator? Not sure
I'm personally interested in the full flush and replace, but what does one have to watch out for when you have a mechanic with the machine and you bring them the ATF to replace with?

Thanks,
Lumberg

It depends on the car make and model, etc. whether you want to DIY or bring to shop.
Some like older Toyota with dipstick, you can do method 3 easily although it is a little bit more time consuming and required patience.
The newer Toyota without dipstick, you can do 1 easily, some I have seen can do 3 if they can find the cooler line.
Although, checking the level is a little bit more involved.
Most old Honda I have worked with, you can only do method 1.

At any rate, the shop can always do method 2 if they have the machine.
Method 3 takes a relatively long process time (more tedious) which is why most shop won't do it.
 
Messages
18,343
Location
NH
I've done the pan drain, refill, then pull a cooler line and pump out one quart. Shut down, refill a quart, repeat. If not shutting down then I'll try to fill at same rate. I'm not crazy about running the pump dry... but I do believe most transmissions will push out at least a quart before any starvation issues.

I like doing a full exchange but if I was starting from new I'm not sure that there is any issue doing just a drain & fill if it was every 30k or so. When the oil coming out is still in good shape then I don't see the gain in the effort of a full flush. But on something with high mile fluid I would do a full exchange.
 
Messages
175
Location
Montague, NJ
On my '16 3.6 Equinox I dropped the factory fill at 45k per the severe schedule and it was black to my surprise. Just did a drain and fill with Amalie full synth. Dex VI and did a drain / fill 30k miles later and it still had a decent red color. No pan or filter access. It has a dip stick and I monitored the color for a few hundred miles after the initial drain and color stayed good so I let it go without being anal about it. It's on a 30k mile interval now.
I'm no fan of running pumps dry either, just like running gas tanks low beating up fuel pumps, disconnecting those quick connect lines is a invitation for leaks IMO also.
Regular changes and using a full synth. fluid is the best course.
I've taken many trannies over 200k miles and sold the vehicles without any issues just doing drain / fills with pan less trannies. Accessible filters get changed though, LiqiVac sucking out fluid makes those pan drops way less messy.
Bottom line is don't let the fluid get so ''toasted'' that a full exchange is necessary.
 
Messages
411
Location
Los Angeles
Not sure what the obsession here is with getting every last drop of old fluid out. Just D&F 3-4 if you're that worried until its diluted significantly and makes no difference. In my kia the pan took around 4.5 qt and total capacity was less than 8 qt. 2 D&F later the fluid was cherry red and shifting like butter.
 
Messages
339
Location
Independence Ky
I think if the torque converter is literally designed to be drained that it's OK to drain it and the pan, then refill the pan with the same amount of fluid, and fire it up.
That’s what I’m thinking, also I’m thinking adding 4 to 5 quarts at a time with a 30 second or so start in between. If I drained the converter and pan then tried to add all of the fluid back at once it wouldn’t have anywhere to go.
 
Messages
2,426
Location
Seattle-ish, WA
I have a follow up question. I plan do do it the DIY way next time (unhook cooling line and dump into bucket). When I observed the BG machine, it showed a steady 1 gal/min which means you'd have two minutes until the trans ran dry (7.9 qt capacity). That's pretty good. But there was a spring inside that sight glass. Is it possible that the flow was being controlled by the spring, and I shouldn't assume a 1 gal/min flow rate from the car's internal transmission pump at idle?

You are correct to not assume that. The internal pump of the AT will flow at a much higher rate. It will take less than ten or 15 seconds to fill a 2qt container in my experience. I position the container so I can see it from the driver's side door or seat so I can kill the ignition quickly. A picture below of doing that recently. Brace the container as the flow will upset it.

Here is a good overview of the procedure demonstrated on a Toyota. I bookmarked this quite a few years ago to share with people.


Position the receptacle so you can monitor the output:

IMG-3210.jpg
 
Messages
5,673
Location
Ohio
Multiple partial drain/refills: the most common DIY method where you drain about a third of the transmission at a time, top it up, start the car and run through the gears, rinse and repeat twice.
I know the OP's vehicle doesn't fall under this, but Honda is very adamant that this is the only acceptable way to service their transmissions and has been this way for a good while. I had a '99 Accord and this method was spelled out in the owner's manual. Doing more than 1x drain-and-refill isn't considered mandatory or required by Honda under normal circumstances either, at least not that I've seen.
 
Messages
453
Location
England
Apologies if this is a stupid question.

Say a car owner changes his ATF. He is using the remove, measure, replace system. His transmission is warm and he removes say 5 litres. He then replaces the 5 litres with new, but cold ATF.
Will the expansion of the warm fluid, compared to the cold, play a factor here? Will adding the same quantity of cold mean too much is added?

I ask, as my W5J400 needs a dipstick and a means of measuring fluid temperature. Easier to replace just what comes out if tranny is operating just fine.

Thank you.
 

Lumberg

Thread starter
Messages
494
Location
Washington DC area
Apologies if this is a stupid question.

Say a car owner changes his ATF. He is using the remove, measure, replace system. His transmission is warm and he removes say 5 litres. He then replaces the 5 litres with new, but cold ATF.
Will the expansion of the warm fluid, compared to the cold, play a factor here? Will adding the same quantity of cold mean too much is added?

I ask, as my W5J400 needs a dipstick and a means of measuring fluid temperature. Easier to replace just what comes out if tranny is operating just fine.

Thank you.
You start with that (add as much fluid as you took out) as the baseline calculation. To be honest you'd probably be fine if you left it, but your trans should have an alternate way of checking the fluid level, such as at the fill hole or an overflow plug, and that's the correct way to fill it.

Also, I'd love to hear smarter peoples' thoughts on this, but I don't think it's the fluid itself that expands and contracts, I think it's the metal in the transmission, that causes the level to change that much with temperature.
 
Messages
175
Location
Montague, NJ
My Tahoe has a trans. temp readout, to get it to the temp. ''spec'' I'd have to tow a heavy load or power brake the crap out of it to get it to temp. on a hot day .
Don't worry about the temp of fluid. My FWD GM trans. have a almost 2 qt. capacity range in their refill specs, and I've never messed with the sight plugs on multiple vehicles in the family fleet.
Drop and refill what came out warm and a few extra OZ. for good luck has worked for me on multiple 200k miles vehicles that did not have dip sticks that were sold shifting just fine.
Trans fluid expansion is not that gigantic of a rate at normal temps., we want fluid at least warm so solids are in suspension when drained.
 
The problem with the trans flush machines is that some of the previous cars fluid is getting pumped into your car when it is in bypass. If your car is fairly new and clean and the one before you had mud flowing through its lines, that mud is going in your car. I have done some on trucks with say, 15-16 quarts of fresh fluid and by the end it still wasn't totally clean but much better. I wouldn't want that fluid going into my transmission personally. Some of them were so nasty that I would put two cases of fluid through them and those were usually pretty red when done. Even used the machine to flush several power steering systems that looked like they had anti-seize in the reservoir.
 
Messages
453
Location
England
Repairman 54, Lumberg.
Thank you for helping.

My W5J400 is Jeeps designation for a Diesel powered MB722.6 if that helps.

It has a dipstick tube but it is sealed. You can get a dipstick and seals easy enough though. This leaves you needing to know the fluid temp and compare on a chart.

A lot of Jeep owners tend to just replace what comes out. Hence my question about fluid expansion.

The following chart shows the check levels. To me it does seem to expand a lot if i am reading it correctly.
3_0L%20TURBO%20DIESEL%20WH%20XH%20NAG1%20FILL%20CHART.jpg
 
Messages
8,144
Location
MI
The problem with the trans flush machines is that some of the previous cars fluid is getting pumped into your car when it is in bypass. If your car is fairly new and clean and the one before you had mud flowing through its lines, that mud is going in your car.
Explain this please. What goes into bypass to cause old fluid from the previous change to get pumped into your car?

Here's the bypass explanation from the T Tech manual:
"The BYPASS FUNCTION simply allows the machine to loop within the system when all the new ATF has exited the cylinder. This function allows the operator to walk away (work on something else, etc.) when the machine is running, without being concerned about service completion. When the piston reaches the top of the cylinder (old ATF has displaced all of the new ATF), the Bypass Function is automatically engaged. This causes the fluid now in the system to be forced into a loop through the vehicle and the T-TECH unit. At this time there is no longer an exchange of fluid and the loop will continue until stopped by the operator by turning off the vehicle."

It seems that the old and new fluids never intermingle with these exchange machines. http://jiffylubecs.gradepoint.com/en_us/doc/T-Tech_Manual.pdf
 
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