Goal for ATF drain and fills, when are you "satisfied?"

Joined
Jul 23, 2021
Messages
818
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PA
Doing drain and fills that will ultimately lead to a pan drop and filter replacement on a high mileage auto, which is a more involved job. But just attempting to get the fluid freshened up in the short term, since it's very simple and relatively mess-free with a Mityvac (excellent tool). I understand that there is a partial fill formula, and each successive drain removes some % of new fluid. This is going to vary based on car and how effective a drain is, whether you have a drain plug or using a Mityvac, and how much you can extract.

This question is not car specific, more generic. When doing short interval ATF drain and fill on a high miles automobile that has visually worn looking fluid, do you shoot for a specific shade of color or an approximate % of new fluid replaced - for instance, approximately 50% or 75% or 90%, etc.?

I have one rig that I've completed 3 iterations and am currently at about 66%, and another 4 qts D&F will get me to about 76%. Fluid is currently a dark cranberry but should be a light cranberry color when new. Thereafter, around 80% on another successive. So even though I'm pulling out good fluid, I'm also eliminating dirty fluid. The question is, when do you think it's good enough?
In this case, the capacity is about 14 qts and I'm replacing about 4 qts each time, and I've worked out the math to be approximately:
1. 30% new fluid
2. 51%
3. 66%
4. 76% new, and draining out about 3/4 of the "new" fluid at this point.
5. 83%
And quickly diminished returns thereafter, draining out almost all new fluid at this point.

The fluid is not expensive, probably $20 for each iteration. Transmissions are expensive, so obviously I'd want newer fluid at a reasonable investment. I'm contemplating doing 1-2 more rounds, and then draining and doing a pan drop and filter swap when I have a full free afternoon to mess with it.
 
Joined
Mar 2, 2004
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3,010
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Kentucky
Depends on the vehicle mileage. If >100K with no prior service history, I'll aim to do 2 or 3 drain & fills in reasonably quick succession. The first one during an oil change for example, and the subsequent ones at each oil change thereafter (so 5-6k intervals). I find after two or three drains the fluid looks practically new (even though there is certainly plenty old fluid remaining) and after that I will switch to every 30k which is my regular ATF drain & fill schedule. On cars with cheap non-synthetic ATF (Dex III for example), I might do a few D/F instead of 2-3.

I figure 50% or so of new fluid is far better than what your average vehicle sees, which is no ATF changes at all.
 
Joined
Aug 14, 2015
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1,897
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CA, USA
When I did it with my Sienna, I did 3 drain & fills over two months, and at about half new fluid each time, got it to 87.5% after the third d&f. That would be enough for me. Doing it any more, would mean that close to 90% of what came out was new fluid--a complete waste. That was the first time I had done it, at the 165K mile mark. It had never been done before. Just because this was the only time its been done, at around 190-95K I'll do another 3. not sure after that, maybe 1, 2, or 3 drain & fills every 30K.
 
Joined
Sep 2, 2005
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7,648
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MIchigan
Tip of the day : I find it much easier to extract fluid with a household vacuum with a crevice tool attachment instead of the Mityvac Handpump.
Remove the Handpump and insert hose into middle of crevice tool and cover remaining opening with fore finger and middle finger. And let'r rip
 
Joined
Apr 25, 2017
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Ohio
The fluid calculator says

Change - % new fluid
# 1 - 28.5 %
# 2 - 49 %
# 3 - 63.6 %
# 4 - 74 %
# 5 - 81.4 %

Remember that this is all strictly mathematical or theoretical. There is simply no way to quantify these values. Using this calculator, for example, you will never reach 100% new fluid. Also, what is considered new fluid ? Having less than 100k miles ? If you replace the fluid every 25k miles, this calculator is only partly useful or accurate.

When I exceed 50-60%, I call it good and after that, just do routine changes vs multiple changes relatively close together.
 
Joined
Aug 11, 2011
Messages
4,716
Location
N.C.
Depends on the vehicle mileage. If >100K with no prior service history, I'll aim to do 2 or 3 drain & fills in reasonably quick succession. The first one during an oil change for example, and the subsequent ones at each oil change thereafter (so 5-6k intervals). I find after two or three drains the fluid looks practically new (even though there is certainly plenty old fluid remaining) and after that I will switch to every 30k which is my regular ATF drain & fill schedule. On cars with cheap non-synthetic ATF (Dex III for example), I might do a few D/F instead of 2-3.

I figure 50% or so of new fluid is far better than what your average vehicle sees, which is no ATF changes at all.
^^^This is what I have done with my 2005 Chevy 5.3 truck. I bought it with 162,000 miles almost 8 years ago. I’ve done probably 7 or 8 siphon and fills during this time extracting roughly 3 qts each time. I’ve used Supertech Dex/Merc non synthetic exclusively and have never dropped the pan. The fluid is a bright pinkish red color and now at 224,000 miles it still shifts like Butta!
 
Joined
Jul 11, 2021
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Close to Sierra mountains
Really ... on a forum based on factual information about oils.


The fluid calculator says

Change - % new fluid


Remember that this is all strictly mathematical or theoretical.
That's right and it was never formulated to be used on any ATX.
Here is where you can prove to yourself that it does not work for servicing any ATX .

 
Joined
Oct 15, 2017
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midpac
Really ... on a forum based on factual information about oils.



That's right and it was never formulated to be used on any ATX.
Here is where you can prove to yourself that it does not work for servicing any ATX .

Please explain what atx is and why you posted a link to the Blackstone homepage.
 
Joined
Jul 11, 2021
Messages
940
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Close to Sierra mountains
Sorry ATX is short for automatic transmission. I forgot which forum I was on. hahaha !

Blackstone does oil analysis. There are dozens if not hundreds of members on this forum that have used them over the years.
The only proper way serving the fluid is using a profession equipment designed to remove and replace in the correct flow direct all the old fluid and replace it with new fluid. The dilution method is a waste of time for so many reasons. I mean if you think about this from anything else you are contaminating new fluid with old. So that in itself is not accounted for in that formal. Also when you do not pressurize the transmission during the procedure much of the contaminates in the form of varnish will remain only to contaminate the new fluid. When a proper professional fluid replacement is done you can actually see when the fluid runs clean.
Everything I just said anyone can verify themselves with at least 2 oil analysis before a pan filter/fluid service and then as short as 3000 miles later.


Look under Transmission on their website:

Automatic transmissions ask a lot of the oil. Not only does the oil lubricate and clean internal parts, but it also functions as a hydraulic oil to operate various components.

Transmission oil can be contaminated with metals, solids, and moisture, and those contaminants need to be removed before they cause problems. Conversely, a test of your transmission fluid may reveal that it’s still in great condition, and you don’t need to change it as often as you thought.

There’s no easier way of knowing what’s going on in the system than oil analysis. We can tell you if the oil needs to be changed, if it’s contaminated, or if there are any problems at hand. Request your free kit today and make sure your drive train is wearing as it should!
 
Joined
May 28, 2014
Messages
1,717
Sorry ATX is short for automatic transmission. I forgot which forum I was on. hahaha !

Blackstone does oil analysis. There are dozens if not hundreds of members on this forum that have used them over the years.
The only proper way serving the fluid is using a profession equipment designed to remove and replace in the correct flow direct all the old fluid and replace it with new fluid. The dilution method is a waste of time for so many reasons. I mean if you think about this from anything else you are contaminating new fluid with old. So that in itself is not accounted for in that formal. Also when you do not pressurize the transmission during the procedure much of the contaminates in the form of varnish will remain only to contaminate the new fluid. When a proper professional fluid replacement is done you can actually see when the fluid runs clean.
Everything I just said anyone can verify themselves with at least 2 oil analysis before a pan filter/fluid service and then as short as 3000 miles later.


Look under Transmission on their website:

Automatic transmissions ask a lot of the oil. Not only does the oil lubricate and clean internal parts, but it also functions as a hydraulic oil to operate various components.

Transmission oil can be contaminated with metals, solids, and moisture, and those contaminants need to be removed before they cause problems. Conversely, a test of your transmission fluid may reveal that it’s still in great condition, and you don’t need to change it as often as you thought.

There’s no easier way of knowing what’s going on in the system than oil analysis. We can tell you if the oil needs to be changed, if it’s contaminated, or if there are any problems at hand. Request your free kit today and make sure your drive train is wearing as it should!

Funny - to me this sounds like a typical dealership's response.

I've done my own work on my vehicles since high school and will continue to do so.
 
Joined
Feb 19, 2009
Messages
716
Location
Upstate, NY
Where im at is a 3X3 method to get everything freshened up, let it be for 1,000 miles, then a pan drop and filter replacement (if you can even drop the pan and change filter)., Fill up, then its good for 20K miles. then a single drain and fill every 20K after.

I've never lost a transmission by changing the fluid regularly. (Well on a automatic SL2, the diff pin went through the case after using M1 synthetic ATF :ROFLMAO: ) But it was not because of the fluid, but because it was towed behind RV......
 
Joined
Dec 24, 2011
Messages
9,610
Location
North Carolina
Then why do numerous OEM's - such as Honda and Ford, specify this as the only approved fluid replacement method in the Service Information?
VW and BMW as well - specify and pan drop and 2x drain and fills when switching to a new fluid type.

So if it is adequate for switching to a new type of ATF, then it is obviously suitable for regular servicing.
 
Joined
Dec 31, 2017
Messages
9,963
Location
SE British Columbia, Canada
I have a Chev 6L90 on which I vacuum pull and replace 3 quarts once a year, and do a pan drop with a new filter and magnet cleaning once every 50,000 miles ( about 5 years). The pan drop is 6 quarts. The Dex 6 darkens a bit in one year. The transmission currently has 220,000 miles and only had a bit on the magnet at the last pan drop.
 
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