How long (miles or days/hours) does new ATF take to circulate after drain & fill

[paulri]

I have decided to not flush out my Sienna ATF, but to do a few drain & fills. Before a month or so ago, it had never been flushed or drained in its 160K miles.

I have done two already, and seen the fluid turn from jet black to reddish brown. I think I will want to do at least one more.

Now after the first drain & fill, I waited a month to see if there was going to be any adverse reaction like the transmission slipping. That didn't happen, so I did it again a week ago.

Now I don't need to wait another month for my next one. But I don't want to simply drain the fluid that I poured down the ATF dipstick, if it went directly into the atf drain pan.

So my question---how long would it take for the new atf that I just poured in, to mix with the stuff that was already there?

 

[ctechbob]

A short drive would probably be all the mixing you would need. When I do a 3x drain and fill I'll drive around the block (Less than a mile) and that seems sufficient.

 

[paulri]

OK, that sounds like it mixes quickly enough--and after your first drain & fill, the fluid that comes out with your second drain isn't much redder than the stuff that drained out the first time (in other words, you aren't just draining out the new stuff)?

Originally Posted by ctechbob
A short drive would probably be all the mixing you would need. When I do a 3x drain and fill I'll drive around the block (Less than a mile) and that seems sufficient.

 

[ctechbob]

You'll be draining out a mix of the old and new. That's the one drawback to drain and fill, always leaving some old behind, and always draining some new out.

 

[PandaBear]

I was told to use each speed / gear about 20 seconds for a few cycles (3?) so a couple blocks if you can reach top gear.

 

[ctechbob]

Originally Posted by PandaBear
I was told to use each speed / gear about 20 seconds for a few cycles (3?) so a couple blocks if you can reach top gear.


That should work too, especially if you want to make sure it makes it everywhere through the valve body, but it will eventually get there without it as well.

 

[GeorgeKaplan]

Your obsession is putting you in a position you are trying to avoid.

The whole idea of doing drain/fill is to not shock the system and induce problems; you know this.

Put yourself on a schedule of doing a drain/fill in the fall and the spring and forget about it in-between.

If you keep doing these closely spaced drain/fills, you might as well get it over with, save time and flush it all.

 

[demarpaint]

A drive around the block should mix it up plenty.

 

[SubieRubyRoo]

Yeah all you need is a 3-5 minute drive that gets the trans to shift thru all forward gears including OD. Honda D&F procedures call it out in this order:
1. Drain & fill.
2. Drive ~5 mins and ensure trans gets all the way to OD.
3. Repeat steps 1&2 three more times.
4. Ensure fluid level is correct on dipstick (Hondas only AFAIK require checking trans with engine OFF).
5. Repeat in about 30k miles.

It's what I follow even on my Subarus. It's a good procedure and gets over 90% of the old fluid out.

 

[tcp71]

A short drive should be enough to mix things up. i would do one more d+f now and then start an annual cycle to maintain it in a lightly used state.

 

[paulri]

Looks like I just need a few mins of driving, then. Not a problem. Thanks everyone.

 

[Hall]

Originally Posted by ctechbob
You'll be draining out a mix of the old and new. That's the one drawback to drain and fill, always leaving some old behind, and always draining some new out.
"Like"

I've always wondered how to measure that and realize there's probably no good way. I have wondered if folks that are well-versed in fluid flow dynamics have actually looked at this and/or ran analyses on this. They could simulate this with a transmission model, existing fluid which they drain a small amount, and new fluid that they add "markers" to analyze. Then again, more and more automakers are more than happy with single drain-and-fills for routine maintenance and for a more thorough fluid exchange, just repeat it 2-3 times. They must feel this ends up with more new fluid than old, which is the key.

 

[Hall]

Honda provided a procedure to their technicians that detailed how to do this without taking the car off of the lift. I'd have to dig it out but it just involved putting it in Drive, applying throttle to get it to switch gears up and down, switching to Reverse, and repeating. It's not a 30-minute process by any means.

 

[WyrTwister]

The torque converter holds a significant amount of ATF .

Lets say , for discussion , 50% . Do a Drain & Fill , you end up with a mix of 50% - 50% old vs new fluid . Do it again and I am guessing 75% new & 25% old . You can see where this is going .

 

[Hall]

There are "calculators" available on the internet that do the math for you. Input total capacity, change capacity, and it gives you a percentage of new fluid content. It's purely mathematical, of course.

 

[paulri]

I'll do one or two more--probably until I'm comfortable with how red the atf looks. The original fluid went 160K, so I won't mind doing this a couple more times if I have to.The math is good to keep in mind, because after a certain point, you are only draining out 5% or less old fluid, and the vast majority new, which is IMO a waste of time. From here on out I think I'll do a single drain & fill every 30K, but for this one, I really do want to be thorough. At least now, I know that I can do multiple drain & fills on the same day.

 

[Hall]

Using the calculator I have, here's some numbers:

Total capacity: 9.3
Drain amount: 3.7

Change # 1 results in 40% new fluid
Change # 2 = 64%
Change # 3 = 78%

When I get above 75% (mathematically), I'm happy. As you continue, the % "new" starts decreasing dramatically. By the math, changes # 7, 8, 9, and 10 look like this: 97.1%, 98.2%, 98.9%, 99.4%.

 

[Yah-Tah-Hey]

It took four drain/refills to get ATF back to out of the bottle look. Now I drain/refill once a year.(four quarts)

 

[JeffKeryk]

I was considering doing a spill and fill with filter change on our GS.
Then running engine for 30 seconds to empty the pan; then repeat maybe 2 more times.

Dunno if it makes sense...

 

[Fifty150]

Originally Posted by paulri
I have decided to not flush out my Sienna ATF, but to do a few drain & fills. Before a month or so ago, it had never been flushed or drained in its 160K miles.

I have done two already, and seen the fluid turn from jet black to reddish brown. I think I will want to do at least one more.

Now after the first drain & fill, I waited a month to see if there was going to be any adverse reaction like the transmission slipping. That didn't happen, so I did it again a week ago.

Now I don't need to wait another month for my next one. But I don't want to simply drain the fluid that I poured down the ATF dipstick, if it went directly into the atf drain pan.

So my question---how long would it take for the new atf that I just poured in, to mix with the stuff that was already there?


You can do this in an hour or two, including prep, clean up, and transferring used fluid into containers for recycling.

Raise your van until the tires are at least 2" off the ground. Support vehicle on jack stands. I like using UniJacks.

Drain & fill. Start the engine, Shift through all of the gears. Do it randomly. Allow the van to reach transmission operating temperature. Shift through all of the gears again.. Turn the engine off. Repeat the process 3 or 4 times. By the 3rd or 4th draining, you will notice that the fluid coming out is almost new. Then refill and check the level.

Drain & fill with fresh fluid. Disconnect the transmission return line,. Not the cooling line. You want the transmission pump to send fluid all the way through the cooling system, so that your transmission cooler is also "flushed" in the process. Route the return line into a bucket. Turn the vehicle on, shift through the gears, and allow 3 - 4 quarts to pump out. Turn vehicle off. Add equivalent amount of fresh fluid back into the transmission. Repeat process until clean fluid runs out of transmission return line. Reconnect the transmission return line. Then refill and check the level.