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ATF Flush vs Drain and Fill #5443863 06/01/20 11:24 AM
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diyjake Offline OP
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What is the verdict nowadays between ATF flush using a machine vs drain and fill.

I was always taught that drain and fill is the only (safe/best) way to change ATF fluid and to avoid using a macing to do a full flush.

To me it seems like true car enthusiasts that like to do their own maintenance strongly discourage using a ATF machine to do a full flush while mechanics / shop owners say using a machine is totally fine and most shops do a full flush with a machine.

Maybe the modern cars are totally fine with using a machine? I do see a benefit using a machine since you get completely fresh fluid but what are the cons?

Re: ATF Flush vs Drain and Fill [Re: diyjake] #5443865 06/01/20 11:28 AM
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RDY4WAR Offline
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I still just do a simple drain and fill every 30-50k miles. I've never been a fan of flushes.


"He who is without oil, shall throw the first rod." - Compressions 9:1
Re: ATF Flush vs Drain and Fill [Re: diyjake] #5443870 06/01/20 11:37 AM
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Originally Posted by diyjake
What is the verdict nowadays between ATF flush using a machine vs drain and fill.

I was always taught that drain and fill is the only (safe/best) way to change ATF fluid and to avoid using a macing to do a full flush.

To me it seems like true car enthusiasts that like to do their own maintenance strongly discourage using a ATF machine to do a full flush while mechanics / shop owners say using a machine is totally fine and most shops do a full flush with a machine.

Maybe the modern cars are totally fine with using a machine? I do see a benefit using a machine since you get completely fresh fluid but what are the cons?


This is from flushing industrial hydraulic systems but the concepts are virtually identical. Other than the labor involved and possibly clean up.....

There's only one advantage and significant difference between a drain/fill versus a "machine"(power) flush- the machine has a much faster velocity of liquid and can recirculate.

In a system where there is significant contamination, sludge, varnish and even pockets of accumulation- a flush will remove this a lot better than a drain. ( I often have to repeat several times for large systems and even do a cleaning fluid flush then purge)

People have argued that a flush can break loose stuff and make a situation worse but I have proven to many clients that not true at all EXCEPT when someone either short cuts the process or does it wrong. We normally have a blotter cell to determine when there is proper particulate cleanliness and its not fooled any more that a coffee filter is with grounds in it.

However, if your system does not have such conditions then there is no other significant benefit or advantage to a power flush over a drain/fill.

Re: ATF Flush vs Drain and Fill [Re: diyjake] #5443874 06/01/20 11:42 AM
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If your car has been shifting fine, drain and fill is a lower risk approach, you have more time to slowly dissolve anything that wasn't loose and less chances of clogging something.

If your car started shifting badly, it is probably too late, drain and refill may get it better but no guarantee. If it still doesn't afterward then you might try flushing as a last ditch effort.

The only gain of a flush is it will replace more fluid faster than multiple drain and refill, hopefully lower labor cost for more fluid cost but it is not guaranteed.


"You keep asking questions PandaBear and you'll end up a vegetarian like my wife" - Camu Mahubah
Re: ATF Flush vs Drain and Fill [Re: diyjake] #5443884 06/01/20 12:04 PM
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I'm yet to see someone who really recommends using a flush machine other than on a hail mary. Consistent drain and fills with filter replacement (if possible) is what i would recommend but I have also had good luck with cooler line fluid exchanges. If you're switching fluids and buy into it being bad to mix them a fluid exchange is what I'd go with instead of a flush.


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Re: ATF Flush vs Drain and Fill [Re: diyjake] #5443894 06/01/20 12:19 PM
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diyjake Offline OP
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Does a machine put in exactly what it takes out? This would be very helpful with a sealed / dipstickless transmission.

Re: ATF Flush vs Drain and Fill [Re: diyjake] #5443904 06/01/20 12:32 PM
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slacktide_bitog Online Content
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Nobody recommends a machine flush, except BG (a snake oil company) and Jiffy Lube and similar quick lubes

One drain-and-fill every interval recommended by the mfr is sufficient smile

If you really need to drain more than that, the best way is to just do 3-4x drain and fills, the interval in between which can be anywhere from a short drive around the block to thousands of miles. And even then, this is rarely necessary unless you went like 200k without ever changing the ATF, or if you used the wrong fluid.

Most cars never get their transmission fluid changed and arrive at the junkyard on their factory fill

Re: ATF Flush vs Drain and Fill [Re: diyjake] #5443942 06/01/20 01:37 PM
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No flushing. Drain and refill. Make sure the fluid level is correct before beginning. If it's a serviceable pan, remove and clean it along with magnets, new filter and new gasket. What came out, put back in. Run it a few hundreds miles and repeat with just the D/R. If you don't have a drain plug, check out Doorman. If you do a simple D/R every 25 - 30k miles or so you'll always have about 80% clean fluid.


2003 Toyota Matrix - Whatever synthetic is cheapest - OEM Filter
2019 Kia Sorento - OEM Filter

“Think of how stupid the average person is, and realize half of them are stupider than that.”
Re: ATF Flush vs Drain and Fill [Re: diyjake] #5443944 06/01/20 01:39 PM
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Are we talking about a fluid exchange vs a drain and fill?

I've heard the term transmission "flush" used quite often and I kind of think that's a misleading term.

A fluid exchange should be harmless and the most effective way to replace transmission fluid. They're designed such that the amount taken out and replaced is exactly the same.

The only potential issue is if you started off with the level low or high, you're going to end the same way.

For the DIYer, if your transmission has an easy means to drain, refill and verify level, a simple drain/fill or serious of them is what I do.

Last edited by JTK; 06/01/20 01:40 PM.

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Re: ATF Flush vs Drain and Fill [Re: diyjake] #5444021 06/01/20 03:06 PM
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I do a drain and fill because I am a diy'er and my transmissions have dipsticks but the newer transmissions that are sealed are probably a lot easier to do with a fluid exchanging machine.

Re: ATF Flush vs Drain and Fill [Re: slacktide_bitog] #5444033 06/01/20 03:18 PM
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bbhero Offline
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Originally Posted by slacktide_bitog
Nobody recommends a machine flush, except BG (a snake oil company) and Jiffy Lube and similar quick lubes

One drain-and-fill every interval recommended by the mfr is sufficient smile

If you really need to drain more than that, the best way is to just do 3-4x drain and fills, the interval in between which can be anywhere from a short drive around the block to thousands of miles. And even then, this is rarely necessary unless you went like 200k without ever changing the ATF, or if you used the wrong fluid.

Most cars never get their transmission fluid changed and arrive at the junkyard on their factory fill

CB I went 283k miles on the original CVT fluid as you know...

I did 3 drain and refills in the next 6,500 miles. It did great doing that. And the last drain and refill a couple of weeks ago will likely be the last one ever done on the ol '08 Nissan Altima VQ two door coupe.


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Re: ATF Flush vs Drain and Fill [Re: diyjake] #5444035 06/01/20 03:19 PM
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bbhero Offline
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Originally Posted by diyjake
I do a drain and fill because I am a diy'er and my transmissions have dipsticks but the newer transmissions that are sealed are probably a lot easier to do with a fluid exchanging machine.

Newer ones without a dipstick.. Just drain out fluid stone cold. Measure and put back in what came out.


Nissan Altima 3.5 Coupe
Royal Purple 10w30 Carquest red 84356
"Treat your family like your friends and treat your friends like your family."
Re: ATF Flush vs Drain and Fill [Re: diyjake] #5444047 06/01/20 03:33 PM
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Transmission Fluid Exchange

For those interested, here's the fluid change method I use on all my cars that don't have a torque converter drain:

1. Pull the transmission dipstick (located near the firewall in most cars). Fresh fluid is translucent and cherry red. Some darkening is normal, but if it is reddish brown or mustard color and smells like burnt varnish, it is worn out.

2. Make sure the fluid is warm.

3. For pans that don't have drain plugs, remove all pan bolts except for the corners. Remove the bolt from the lowest corner, then loosen the other corner bolts a turn or two. Carefully pry the pan to break the gasket seal at the lowest corner. Drain mostly from this corner. With good technique you can avoid or at least minimize the red bath.

4. Remove pan. Inspect the pan before cleaning. A small amount of fine grey clutch dust is normal. However, if you find metal shavings, there has been transmission damage. Remove all old gasket material. Clean the pan and magnet with solvent and wipe dry so there is no harmful residue. Shop air can be used to clean the magnet. Hammer back any pan damage from previous overtightening.

5. (Optional) Drill hole in pan at low point and install a drain kit available from most auto supply houses. Make sure the kit protruding inside the pan doesn't interfere with anything on the transmission.

6. Replace filter. If it’s a metal screen filter, it can likely be cleaned and reused.

7. Position gasket on pan. Some gaskets have four holes slightly smaller than the rest to allow four bolts through the pan and through these smaller holes to hold the four bolts and gasket in place.

8. Hand tighten pan bolts in a criss-cross pattern. After that, use a torque wrench to tighten bolts to proper ft-lbs as per manufacturer.

9. Refill the transmission using only the amount shown as “refill capacity” in the owners manual (or an equal amount that was drained), using the type of fluid specified for the vehicle.

10. You now have replaced the trans fluid and filter according to manufacturer’s requirements. Fluid is changed in the pan only.

You can stop here and go to Step 17 if you just wanted a regular drop-the-pan fluid change. For a complete exchange of the fluid (including transmission body and torquer converter) continue with the next steps.

11. Obtain the total system capacity of the vehicle from the manufacturer. Have this amount - plus a bit more - of fluid readily available.

12. Disconnect the oil cooler line from the transmission cooler. Tickle the ignition to find the flow direction. Direct the stream of fluid toward a receptacle. It is better to use a clear length of hose with a shoplight laying next to it so you can see when all the old fluid has left the system.

13. Start the engine, let it idle to pump out old trans fluid until you start seeing air bubbles.

14. Stop the engine. Refill transmission through fill tube with fresh fluid - same amount as pumped out (usually about 2-3 quarts). After the first iteration, it helps to shift the transmission through the detents, pausing at each one, to get the old fluid out of the circuits.

15. When either the fluid color brightens or the total capacity has been replaced, shut the engine off and re-attach the oil cooler line. All trans fluid has now been changed.

16. Button everything back up. Clean up the mess.

17. Recheck the fluid level. With the car on level ground, set the parking brake and the transmission in “Park” or “Neutral.” Let the engine idle for a few minutes. Shift the transmission through all detents, pausing momentarily at each position, before returning the lever to “Park” or “Neutral.” Check the fluid level again and check for leaks. Refill fluid so it is slightly undercharged. This way it can be properly checked and topped off after a long drive.

Re: ATF Flush vs Drain and Fill [Re: diyjake] #5444060 06/01/20 03:50 PM
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If you have the time and tools a regular drain, fill, and occasional filter change is fun and will work great. There is nothing wrong with a fluid exchange every 50-80K either.


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Re: ATF Flush vs Drain and Fill [Re: diyjake] #5444062 06/01/20 03:53 PM
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Numerous manufacturers recommend a line off fluid exchange, I find it the best and least expensive way. Drain and fill is very wasteful and somewhat ineffective until a lot of fluid ($$$) has been run through and mixed in.
I do a pan drop and change the filter first then refill and let the fluid go into a container through the return line.
The new fluid pushes the old fluid out, just do about 3/4 of the sump capacity at a time until the fluid coming out is the same color as it is going in then check the level.


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