Completely Flushing a 240k mi Automatic Transmission

If you google “automatic transmission maintenance” it’s not long before you find some number of folks who will tell you that flushing an older transmission will cause damage or slipping. The idea has always been that the old burnt and gritty fluid adds friction and helps the old transmission “grip”. Since this isn’t reflected in Aisin or Toyota maintenance protocols (to my knowledge) I tried to find any objective or measurable data supporting this claim. All I found were old mechanics saying “trust me”.
I don’t mean to cast aspersions on the hard-won wisdom of years of experience, but being a nurse and EMT, I am very wary of practices that are based on little more than hearsay and “sound logic”. I’d prefer large-scale real-world data.
I decided I wasn’t going to damn my transmission to a life of sub-par maintenance based on an unsupported wives tale - so I resolved to replace the entire 12 quart capacity of old tired fluid.

I used the Timmy method cited here:
https://youtu.be/RumPXivBlk8

I opted for the 3/8” inner diameter clear hose. I found it very easy to see when old fluid changed to new fluid in the process. The transmission on my 2001 automatic DCSB V6 took 3 gallons to replace. I replaced with full synthetic Valvoline ATF high mileage. The gallon jugs have graduated marks on the side which make titrating the fluids simple enough. the whole process did require my wife helping me out with starting the truck a few times, but it was simple and pretty satisfying seeing the maple syrup turn to ruby red ATF.



After 1000 miles of mixed highway/city/dirt road, I have noticed no big change in shifting. Sometimes I felt as though it didn’t hesitate as much at high speeds, but that’s probably my imagination.

Using a scan tool I noted the ATF temp sensor ran 180-190F when warm on highways before the flush. After the flush, I actually had a difficult time getting it up to 180F in order to properly recheck the level. Now it runs about 160-170 when warm on the same highways carrying about 400lbs of weight in the rear. Testing was done at ambient temperatures of about 72F.

In the absence of evidence-based consensus on this topic, I thought others might benefit from hearing my anecdotal experience. I wouldn’t hesitate to do this again. My dad recently bought a 2000 Land Crusier with spotty maintenance history and I plan on fully refreshing that transmissions fluid as well.

 

All the issues that arise that I hear is because they did a "flush". A drain and fill is the way to go. But yes you're right, there's never any evidence supporting that a flush kills an old trans.

 

I can't fathom the notion of changing the fluid and NOT putting in a new filter. Done it lot's of times on other vehicles. It's not that difficult, and you get to wipe the sludge out of the pan ;-) A real "feel good" sort of thing.

 

When I first got the truck years ago I emptied the pan, replaced the filter and cleaned the magnets. Definitely satisfying to clean the gunk. That said, draining the pan only changes about 1/3 of the fluid inside the transmission. In this process I already knew my pan filter and magnets where relatively clean (were done 5 years ago) so the flush was to bring ALL of the fluid back to new.

FSM says draining the pan and refill is a 30k interval. With old burnt fluid, I doubt you will ever get back to a as-Toyota-intended state of fluid with intermittent partial changes.

That being said, I don’t begrudge someone who opts to stick to the FSM schedule. I’m sure if mine was done from mile 0, there would be no need to flush. Alternatively if the transmission runs fine, maintains good temps, and you are gentle on the transmission, it’s hard to argue with sticking to the FSM schedule.

 

The automatic transmissions in these trucks dont have a typical "filter" it's a very fine screen. I used to replace the screens on jeep XJ's but there was never really anything clogging the screen. A friend of mine who was big into XJ's said he never replaced them. So i have have skipped replacing them a few times as well as long as the fluid was clean.

The damage from tranny flushes come from the professional machines that uses pressure to clean them out. If you just take a tranny cooler line off thats just flushing the converter at standard pressures and shouldn't hurt anything. I have "flushed" many Asian AW4 transmissions (same as Tacoma) in my driveway and never had any problems.

 

Same as 07 above, that screen doesnt catch much.
I would fore go even cleaning mine again, instead just stuck one of those in-line Raybestos mag filters or whatever,
and just toss that every 30k.

If you have an unknow tranny or its way way past its change, scotty says save that old fluid - just in case...

Myself I use the reg Lubegard additive, they make a friction modifier that they swear by......instead of retreating to the old fluid....

Really the asin trannys with solenoid shifting dont seem to be as sensitive to shift/slip problems......more than likely if you baby it.....it will be your torque convertor that goes first.

$13 Lubegard 60902 Automatic Transmission Fluid Protectant, 10 oz

Amazon.com: Lubegard 50902 Automatic Transmission Fluid Protectant, 32 oz : Automotive

 

On my old Chevy we had a flush done. It washed some crap into the valve body ad the transmission behaved horribly - dropping out of gear and whatnot. $100 for a new valve body and never an issue after. That 4l60e was at 225k when we sold the truck


Just an anecdote with a happy ending, and I think the lesson I take is that a flush may be fine, but it might also give you more work to do

 

Yes, these transmission filters are not like the oil filters which benefit from regular changes. What is beneficial is cleaning the magnets that sit at the bottom of the transmission pan. Those are what trap fine metal particles that end up down there. Since the force of magnetism increases the closer you are to the magnetic source, these magnets don't "clog" but rather are just less effective when covered in a thick layer of grit. I personally like to drop the pan on a new-to-me vehicle as a way to assess the quality of fluid, state of the magnets, and also see evidence of possible transmission services in the past.
As I said above, my filter was new and magnets were cleaned as of about 5 years ago, and don't feel the need to do that again now.

Luckily I am not in need of friction modifiers right now but I will keep an eye out of Lubegard if that need should arise.

Additives are always a hot topic since it is difficult to suss out what is effective and what is just snake oil. The same goes for detergents. I try to use them within reason, but I never know whether or not I'm just throwing my money away - especially with detergents.
I forgot to mention above that I ran Seafoam Trans Tune for 100 miles before I flushed.

 

Most of the flush failure stories are people trying to fix an already failing transmission with a flush. Then blaming the flush when the trans lets go, not blaming preexisting conditions that precipitated the flush idea

 

Yeah cleaning the magnets is important. I also run a Magnefine inline transmission filter with magnets in it to catch anything before it ever makes it to the pan. And i change it every once in a while so i dont have to drop the pan as often.

https://magnefinefilters.com/NEW-Magnefine-3-8-Magnetic-Inline-Transmission-Filter-R038M-3810000.htm

 

If you do drop your pan......doesnt hurt to thro in couple extra of those tiny neo magnets ...
Like I said....not planning on going back.

 

This topic always get me goin'. Image you didn't change your engine oil for 80k miles, then you finally did an oil/filter change and your engine blew shortly after. Then you go around telling everyone that oil changes are bad and you shouldn't do them. No the fact you neglected the engine for so long is why it blew not because of the oil change. It always annoys me. Also no one ever investigates the root cause of the transmission failures just "assumes" the flush was what caused the failure.

 

This right here,, even though I don't have a auto, family cars have always been auto. People need to look into a BG trans service, if the auto has no issues already it's totally safe to do the BG service,, total fluid exchange, not a flush. Do the research on it, they make very good services and products.

 

MOST of the debris floating around in an AT is clutch plate friction material.
Fibers of one sort or the other. Not good for small passages. orifices, and check plates. A "flush" knocks them loose only to show up where it's not wanted.

Change that filter!

If you are concerned about changing ALL of the fluid, Just start the engine with the pan dropped.
What fluid is in the Converter will get pumped out.

My bet is the engine could be run for 5 minutes without damage to any bearings or internal component. Probably takes less 1 minute to pump out the TC.

I've rebuilt three Slush boxes. (5HP24a , 4HP19 , 4L30e They start out empty. ;-)

 

@VTCAL The method I used to empty all the fluid was using just disconnecting the "send" hose going from the transmission to the radiator and just turning the engine on. As it empties quart by quart, I replace with new ATF until the fluid being drained looks like new. This was the method used in the above video, it sounds like the same idea you mentioned but does not require dropping the pan for those of us who have done that recently enough to not warrant it.