change transmission filter before or after the full fluid flush?

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May 27, 2023
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hey all im planning to do a full fluid flush for my tranny to swap out all 10-12 quarts and put in fresh fluid. i also want to change the filter to have peace of mind for the future. however i have two scenarios that are causing a dilemna and not sure what to do

Vehicle is 2015 Rav 4


1. if i pan drop, dump out the old 4 quarts, take out the filter, install new filter, fill up 4 quarts, and then start the flush procedure, then 6-8 quarts of the remaining old dirty fluid will end up dirtying my new filter a bit? because i assume when i take off the cooler line and start the flush procedure the new fluid will push the old fluid thru the tranny and then the old fluid will come out but at the same time the old fluid will dirty my new filter?

2. method #2 is that i disconnect the cooler line, dump out whatever fluid that comes out, add in new fluid, then dump out more then add in etc. and then when im almost done my flush, drop the pan, change the filter. and then replenish with whatever amount of fluid the pan would take. but then this way the new fluid would end up going thru the old filter and end up becoming 'dirtier' then new

i don't know if maybe my schematic of transmisison fluid and cooler lines and what fluid is coming thru the filter is correct, but if my scenario's above are correct then it seems like both ways the new fluid won't really truly be new. i also feel like method 1 is easier.

any ideas or am i really overthinking?

thx
 
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First off, what vehicle is this on?

I would opt for dropping the pan, changing filter and refill. Then in a few weeks or so, drop the pain (or if you have a drain), and refill the transmission. Maybe after that, once more. But at that point you'd have some very clean fluid in there.
 
What year, make and model is this? Some care are super easy to a line off exchange while others have a thermostat in the transmission or the line making it a bit more difficult. In any case doing multiple drain and fills is a wasteful and time consuming procedure.
 
I would drop the pan and change the filter. Then do the cooler flush method before adding any new fluid, I would make sure no more came out the cooler hose. Then fill the pan with a good amount and run the cooler hose open until new fluid comes out. Then button up and top off.
 
As long as the old filter wasn't completely clogged and bypassing, the old fluid will only have a tiny amount of filterable material in it, certainly not enough to load up a new filter (unless the new filter is way more efficient for small particles). I'd just do what's most convenient.
 
Personally I would use your method #2 and remember that the filter's job is to REMOVE contaminants, not add them back into the fresh fluid...so, yes you are over-thinking this. ;)
 
What year, make and model is this? Some care are super easy to a line off exchange while others have a thermostat in the transmission or the line making it a bit more difficult. In any case doing multiple drain and fills is a wasteful and time consuming procedure.
I wouldnt make a blanket statement of "time consuming"
The wife's old accent had a drain plug. I could drain out the 3qts and refill in about 3-5min. Drain plug on the pan.. and dipstick funnel to refill.
Did it every 15-20k miles.. Wasteful.. probably. Cheaper? Much.

Now my 2002 ranger.. The line off into a bucket flush worked great
 
hey all im planning to do a full fluid flush for my tranny to swap out all 10-12 quarts and put in fresh fluid. i also want to change the filter to have peace of mind for the future. however i have two scenarios that are causing a dilemna and not sure what to do

Vehicle is 2015 Rav 4


1. if i pan drop, dump out the old 4 quarts, take out the filter, install new filter, fill up 4 quarts, and then start the flush procedure, then 6-8 quarts of the remaining old dirty fluid will end up dirtying my new filter a bit? because i assume when i take off the cooler line and start the flush procedure the new fluid will push the old fluid thru the tranny and then the old fluid will come out but at the same time the old fluid will dirty my new filter?

2. method #2 is that i disconnect the cooler line, dump out whatever fluid that comes out, add in new fluid, then dump out more then add in etc. and then when im almost done my flush, drop the pan, change the filter. and then replenish with whatever amount of fluid the pan would take. but then this way the new fluid would end up going thru the old filter and end up becoming 'dirtier' then new

i don't know if maybe my schematic of transmisison fluid and cooler lines and what fluid is coming thru the filter is correct, but if my scenario's above are correct then it seems like both ways the new fluid won't really truly be new. i also feel like method 1 is easier.

any ideas or am i really overthinking?

thx
Filter is a rock catcher.
Skip that and put a magnefine filter in line.
 
I am not seeing any argument to flushing, replacing filter, and refilling. Keep your new filter unexposed to old fluid and contaminants. Is there some nuance I'm missing on this whole thread? If your car is one where you are supposed to do a few drains and replacements, same story.
 
hey all im planning to do a full fluid flush for my tranny to swap out all 10-12 quarts and put in fresh fluid. i also want to change the filter to have peace of mind for the future. however i have two scenarios that are causing a dilemna and not sure what to do

Vehicle is 2015 Rav 4


1. if i pan drop, dump out the old 4 quarts, take out the filter, install new filter, fill up 4 quarts, and then start the flush procedure, then 6-8 quarts of the remaining old dirty fluid will end up dirtying my new filter a bit? because i assume when i take off the cooler line and start the flush procedure the new fluid will push the old fluid thru the tranny and then the old fluid will come out but at the same time the old fluid will dirty my new filter?

2. method #2 is that i disconnect the cooler line, dump out whatever fluid that comes out, add in new fluid, then dump out more then add in etc. and then when im almost done my flush, drop the pan, change the filter. and then replenish with whatever amount of fluid the pan would take. but then this way the new fluid would end up going thru the old filter and end up becoming 'dirtier' then new

i don't know if maybe my schematic of transmisison fluid and cooler lines and what fluid is coming thru the filter is correct, but if my scenario's above are correct then it seems like both ways the new fluid won't really truly be new. i also feel like method 1 is easier.

any ideas or am i really overthinking?

thx
If it has a filter:
- drop pan and change filter/ refill with fluid and keep track of how much fluid you put in.
- pull off whatever hose you are using to do the flush with, extend it to some place you can use a measuring container that is marked in Qts(walmart sells those 6Qt clear jugs), start the vehicle and pump out half a qt less than you put in the pan when you changed the filter, shut off the engine(be ready as it fills up fast)
- add same amount of new fluid to the pan, repeat until you have ran through the rated capacity of the transmission.


There is no contamination of the new fluid from the old if you pull the correct hose. No old fluid goes back to the pan, the pump picks up the new fluid and forces the old out. I do all of our vehicle in the above manner, you just have to know which hose to pull from where.
 
If the pan and/or TC has a drain plug, or you can suction out from the dipstick tube, I’d do that, replace the removed fluid, drive a while to full hot, then do the pan drop and filter replacement. Intent is thst while you won’t get it perfect, you’ll get some of the old fluid diluted, and the new fluid detergent and dispersants can help clean anything that might need it for a bit, before full new fluid and a new filter.
 
If it has a filter:
- drop pan and change filter/ refill with fluid and keep track of how much fluid you put in.
- pull off whatever hose you are using to do the flush with, extend it to some place you can use a measuring container that is marked in Qts(walmart sells those 6Qt clear jugs), start the vehicle and pump out half a qt less than you put in the pan when you changed the filter, shut off the engine(be ready as it fills up fast)
- add same amount of new fluid to the pan, repeat until you have ran through the rated capacity of the transmission.


There is no contamination of the new fluid from the old if you pull the correct hose. No old fluid goes back to the pan, the pump picks up the new fluid and forces the old out. I do all of our vehicle in the above manner, you just have to know which hose to pull from where.
Thank you, I watched some videos and seems like every pulls one of the cooler return lines. Is that the one you would recommend too?

My confusion is this and wanted to confirm
When I drain the pan. And add new fluid. Then when I start the vehicle the new fluid will enter the filter and then circulate in the trans and then would push the old fluid out from the cooler lines. And since I would disconnect one of the cooler lines then all the old fluid would be diluted up in the trans/ pushed out of the cooler lines. Once I noticed a Color change then I would be done

However wouldnt the new pan fluid have to enter the filter when it circulates the tranny? If so that’s what I was curious if it would dirty the fluid

Thx
 
As I understand the cooler lines are connected to the torque converter as the last path before the pan return, also the hottest area. You will only get fluid out of one hose other that dribbles. The filter is the pickup. So if the pan is full of new fluid. When you start the purge new fluid goes though the trans and exits the cooler line.
 
Thank you, I watched some videos and seems like every pulls one of the cooler return lines. Is that the one you would recommend too?

My confusion is this and wanted to confirm
When I drain the pan. And add new fluid. Then when I start the vehicle the new fluid will enter the filter and then circulate in the trans and then would push the old fluid out from the cooler lines. And since I would disconnect one of the cooler lines then all the old fluid would be diluted up in the trans/ pushed out of the cooler lines. Once I noticed a Color change then I would be done

However wouldnt the new pan fluid have to enter the filter when it circulates the tranny? If so that’s what I was curious if it would dirty the fluid

Thx
Yeah, you should have 2 hoses going to either a radiator type cooler or to a heater exchanger somewhere, can probably find which hose via a youtube vid. You pull the hose that goes into the cooler. The new fluid you put in the pan will be drawn through the filter by the pump, the pump will be pumping new fluid to the tranny and pushing the old fluid out.

Our Escape and Mazda 5 are easy to tell when you transition from old fluid to new fluid, the Armada, I just have to go by volume as the old fluid always looks just as good as the new fluid does. I flush them every 50K or every 10th oil change.
My old F150 has a drain plug in the torque converter and a drain plug in the pan so I can get almost everything out of it without needing to pull hoses.
 
The easiest way is to get a magnifine filter. Find some rubber cooler hose and inset it permanently. Then when flushing just put both ends in a bucket. No need to worry about which is coming or going.
 
As I understand the cooler lines are connected to the torque converter as the last path before the pan return, also the hottest area. You will only get fluid out of one hose other that dribbles. The filter is the pickup. So if the pan is full of new fluid. When you start the purge new fluid goes though the trans and exits the cooler line.
sound's good does pickup mean when the vehicle is started then the new fluid is picked up off the pan and goes thru the filter?

if so then seems like i should pan drop, change filter, reinstall pan. start the purge. and then seems like alot of the new fluid won't be mixed with old since it will just mix with whatever is on the walls of the tranny and whatever is in converter which will then get pushed out of the tranny cooler return line which is aiming at a bucket. after a 1-2 gallons is added should just end up being new fluid that is hitting that return bucket

correct me if im wrong

thx
 
On my daughters 08 Lexus rx350, I did a drain and fill only at 143k miles. At 150k I will drop the pan, replace filter and fill w new fluid. That will be good until well after 200k
 
if i just unhook the cooler line at the start and drain fluid from there rather then pan dropping at the start does that benefit me at all?
or is it best to just pan drop, drain fluid, and then fill and do the cooler line drain
 
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