Complete Transmission Flush!

mashley · Sep 28, 2018

Recently I discovered that disconnecting the tranny oil return line is the cheapest way to exchange ALL of the oil in one go, and very easy!

Just extend the return line from the tranny cooler with some clear hose and a barbed fitting into a gallon container, marked at 1qt intervals so you can watch it fill on the ground just outside the drivers door.

Turn the key and let it fill 1quart then turn the engine off (running 1qt low wont damage your transmission. IF you correctly determine the level to the high marks on the dipstick prior. Be sure to use the procedure defined in user manual)

After 1 quart has drained, turn the ignition off then go and pour 1qt into the top of the transmission via the refill plug.
Repeat this until the oil runs clear. Done!

You'll find that you only used 1 to 2 quarts more than the total capacity of the transmission. It's almost as straightforward as a drain and refill but it's actually less messy! This technique has been a revelation to me after having used the “standard” multiple drain and refill technique for years and managing only to exchange part of the oil each time which although good, it's not ideal.

The ignition on and off method can be achieved with one person only, and at no risk of over or underfilling or trying to keep up if the engine is constantly on.

CroMath · Sep 28, 2018

Very nice, except that it doesn't work. If you're not running through all the gears while you do this, you aren't getting all the fluid.

Honda automatic transmissions are different from most others. There's a reason why even the dealership shop manuals don't do this, and it isn't because no one at Honda ever thought of it.

mashley · Sep 28, 2018

CroMath said:
Very nice, except that it doesn't work. If you're not running through all the gears while you do this, you aren't getting all the fluid.

Honda automatic transmissions are different from most others. There's a reason why even the dealership shop manuals don't do this, and it isn't because no one at Honda ever thought of it.

That's interesting, I did my girls chevy cruze a few weeks ago and did cycle through the gears just in case, I guess it was unnecessary.

So, in the Odyssey we can with the "parking brake on" cycle through the gears and achieve the full flush right?

CroMath · Sep 28, 2018

mashley said:
That's good to know, I did my girls chevy cruze a few weeks ago and did cycle through the gears.

So in the Odyssey we can with the "parking brake on" just cycle through the gears to achieve the full flush right?

By "cycling through the gears" I mean that you have to get the transmission to go into reverse and then to change from first to second to third to fourth to fifth sequentially. It's not just moving the shifter through P-R-N-D-L and back with the parking brake on.

In a shop, this can be done by raising the vehicle on a hoist and "driving" it while in the air up to about 50 mph (you're almost certainly in fifth gear by then). But getting all four wheels off the ground to do this is far easier and safer in a shop setting. For us weekend warriors in our driveways trying to save a few bucks, I think that procedure is more complicated than simply doing a drain-and-fill and then driving a bit on the street and repeating as often as you feel necessary. The drain-and-fill can be done completely at ground level; there's no need to even raise the front of the van, much less all four wheels. Even though it uses a couple extra quarts of ATF, the triple drain-and-fill is easier, safer and better.

mashley · Sep 28, 2018

Ahhh, well that's a shame I really was kicking myself for not having adopted that method prior.

I am curious though what the percentage exchange would be with the parking brake on and slowly cycling with low gears then reverse,
are you saying that this is just simply no better than a drain/refill then? (wheels have to be spinning)

I know that these tranny's are a hybrid and considered a little backward/unusual for not using the planetary style.

CroMath · Sep 28, 2018

mashley said:
Ahhh, well that's a shame I really was kicking myself for not having adopted that method prior.

I am curious though what the percentage exchange would be with the parking brake on and slowly cycling with low gears then reverse,
are you saying that this is just simply no better than a drain/refill then? (wheels have to be spinning)

I know that these tranny's are a hybrid and considered a little backward/unusual for not using the planetary style.

You don't need to kick yourself for anything. Honda automatics really are a different kind of animal.

The wheels do have to spin, because that's the only way to engage all the gears and open all the necessary passages inside the transmission to get all the fluid to circulate. The emphasis here is on the word "ALL". There are a number of ways to get most of the fluid, but the drain-and-fill on the ground is still probably amongst the easiest. It's why even the factory shop manual tells the dealership's factory-trained mechanics to use the drain-and-fill technique; it's the easiest way to get the best results.

I do not know the exact quantity of fluid trapped inside the transmission when the vehicle is stopped, but I do know that it takes about 11 quarts to do a triple drain-and-fill (based on roughly 3.7 quarts available to drain out; you may get a little more or a little less) and that exchanges about 85% of the ATF, leaving in the neighbourhood of 1 quart of the original fluid load inside, but very thoroughly diluted. I would think that your method is probably getting a similar result.

There isn't anything inherently bad about exchanging the ATF through the return line; a fair number of people around here have done it that way and have lived to tell the tale happily. You just shouldn't be under the impression that you're getting all of the old ATF out that way. You get most of it, just like the drain-and-fill method.

marvinstockman · Sep 29, 2018

The real point being, and unless the trans has burnt fluid or the wrong fluid, you don't have to get all the old fluid out.

egads · Sep 29, 2018

The procedure CroMath describes is right out of the Service bulletin Honda put out for the 2011+ transmissions that require a software update and complete fluid replacement. That is, as marvinstockman says, because the fluid is burnt and degraded.
Changing the trans fluid is all about dilution. This is a difficult concept for some folks. It is one I use on my aquarium weekly. Remove 10-15% of the water and replace it. Changing all the water at once is very bad. Shocks the system and the fish.
I have been doing the trans fluid in my 02 since I bought it with about 36k every other oil change or about every 15k. I am now at 230k on the original transmission! So regular changes can work. (and I'm probably living on borrowed time)

If anyone is interested in why a Honda automatic is not like any other, here is the story:

https://world.honda.com/history/challenge/1968hondamatic/index.html

DrD · Sep 30, 2018

Since it's a recirculating system, you can't really remove 1 quart of old fluid at a time this way - seems more like a faster way to do the multiple drain/refill process, so the each time you drain, you remove a mixture of old/new fluid, but you don't cycle through the gears so there are some regions which don't really get flushed until you drive. Who knows if it's more or less effective - if it's less messy, and easier for you to do, I can't see any harm in doing it that way.

Denis · Oct 1, 2018

Trans fluid change

I have owned two transmission rebuilding shops for years. Just open the drain plug and drain out as much as you can. It will drain 3-4 quarts. Put in new fluid-use a synthetic that is defined in your owner manual. IF you just can't stand it and want to replace more fluid do it once a year or every two years. There are no products of combustion as in your engine oil. You are changing out a hydraulic fluid it's a completely different application for a lubricant vs. the engine. Put on an additional transmission cooler is best and don't overheat the engine. Meanwhile don't obsess over this topic as many here do.

egads · Oct 2, 2018

The Honda transmissions have gotten better as time and redesign go on. Keep in mind that an every other oil change is using either the mileage based 7500 interval or the newer down to 15% that seems to average 8000 miles. So every 15 or 16 K is hardly obsessive. Kind of like once a year. More like prudent. One of the reasons this does get stressed so much around here is because most automatics have no fluid change interval at all. It is not on the radar of new Honda owners. Those of us who had and still have 2nd gen vans had reason to be obsessive.

davedrivesody · Oct 2, 2018

DrD said:
I can't see any harm in doing it that way.

I generally agree that a self-powered flush has the same result as multiple drain and fills.

However, I see two possible downsides to the flush over the drain:

1. No chance to clean the magnet on the drain plug. Unless you have a Magnefine, this magnet plays an important role in reducing ferrous particles suspended in the ATF.
2. Risk of leakage at the cooler line connection.

Dave

mashley · Oct 2, 2018

Transmission cooler

Denis said:
I have owned two transmission rebuilding shops for years. Just open the drain plug and drain out as much as you can. It will drain 3-4 quarts. Put in new fluid-use a synthetic that is defined in your owner manual. IF you just can't stand it and want to replace more fluid do it once a year or every two years. There are no products of combustion as in your engine oil. You are changing out a hydraulic fluid it's a completely different application for a lubricant vs. the engine. Put on an additional transmission cooler is best and don't overheat the engine. Meanwhile don't obsess over this topic as many here do.

I have recently purchased a possibly too oversized - B&M 70273 Tranny "Supercooler", living in New Orleans the heat and humidity is pretty high here about half the year.

1) Is is possible to run this Ody tranny too cool, is this cooler overkill?

2) What are the ideal temps one should be seeing through a scan tool?

3) These Ody's run the trans through the shared engine coolant radiator primarily, so will adding a trans cooler help slightly with the engines coolant efficiency? (just curious)

https://www.flowmastermufflers.com/...i-tek-cooler-small-supercooler-15000-btu-rating-npt-fittings-plate-type-black/?

mashley · Oct 2, 2018

Answered my own questions>

However, if anyone has anything to add to reference for all of us to read, please

Transmission Cooler: The Definitive Guide | Transmission Repair Guy

Transmission Cooler: The Definitive Guide | Transmission Repair Guy

davedrivesody · Oct 2, 2018

mashley said:
Is is possible to run this Ody tranny too cool, is this cooler overkill?

Hard to say if this cooler is overkill. It depends on climate, topography, van load, etc.

I don't think the ATF temperature is available through the OBDII port on the Gen 3 Ody. However, you could get an idea with an infrared thermometer.

If your ATF is in fact overcooled, one solution would be to add a thermostatic bypass. That would give you a good ATF operating temperature over the full range of ambient air temperatures.

Dave

waveform · Oct 5, 2018

How much more waste is created with triple drain and fill? I was just at the dealership today and they said three times, I thought it was so rediculuise. The point of using the drain is its the lowest point in the system. It seems with the torque converter and all the little cavities its like 8 quarts from factory.

DrD · Oct 5, 2018

davedrivesody said:
1. No chance to clean the magnet on the drain plug.

That's a good point.

mashley said:
Is is possible to run this Ody tranny too cool, is this cooler overkill?

Looks pretty similar to the unit we have on our Odyssey now (most of the remanufactured transmissions come with a giant cooler of some sort - I think the OEM one in the radiator is undersized)
No danger in running it too cool.
As to efficiency of the radiator, maybe, as you are dumping less heat into the coolant, but I imagine the difference is pretty negligible

waveform said:
How much more waste is created with triple drain and fill?

Each drain/fill is about 3.3 quarts, so three cycles is 10 quarts or so. Make sure you bring it to a recycling center.

CroMath · Oct 6, 2018

waveform said:
How much more waste is created with triple drain and fill? I was just at the dealership today and they said three times, I thought it was so rediculuise. The point of using the drain is its the lowest point in the system. It seems with the torque converter and all the little cavities its like 8 quarts from factory.

As DrD already mentioned, it will take about 10 quarts to do a triple drain-and-fill. That is important to know, since it is the quantity of ATF you will be transporting to your nearest household hazardous waste disposal station.

However, after putting those 10 quarts through the transmission, you will have diluted out about 7 of the 8 quarts that are inside the transmission to begin with. So in reality, only 3 quarts out of the 10 are genuinely wasted, in the sense that you haven't received the full benefit of what they have to offer as brand new ATF. That is why many of us (me included) don't do all three drain-and-fills in the same day - that is a very drastic measure that is really called for in only the worst cases of neglect. If you leave some time between drain-and-fills, like a thousand miles of driving or so (if this is simply a general maintenance item for you, this is perfectly OK), then the newer fluid that gets drained out isn't totally wasted. It gets a chance to circulate and do some cleaning inside the transmission before being disposed of.

Glennda5id · Oct 9, 2018

Three drain and fills will leave you with 1.62 qts of old fluid and 6.37 qt of new fluid. Which is 80% fresh fluid.

CroMath · Oct 9, 2018

Well if we're going to be pedantic about this, let's go all the way:

Basic assumptions:

- The ATF capacity of the transmission is 8 quarts, and your transmission is filled to the proper level before you begin.
- You drain out the same quantity of ATF each time you drain and fill (D&F)
- Formula: %new = 100 - [((8 - (quarts drained))/8)[SUP]n[/SUP]]*100, where n is the number of drain and fills completed.

I've seen this formula presented before (in one form or another), but let's just make life easier for everyone and turn it into a reference chart. I have chosen to use drained values between three and four quarts because it seems rare that people get fewer than three or more than four quarts out in a single drain.

Quarts drained	% new - 1 D&F	% new - 2 D&F	% new - 3 D&F	% new - 4 D&F
3	37.5	60.9375	75.5859375	84.74121094
3.1	38.75	62.484375	77.02167969	85.92577881
3.2	40	64	78.4	87.04
3.3	41.25	65.484375	79.72207031	88.08671631
3.4	42.5	66.9375	80.9890625	89.06871094
3.5	43.75	68.359375	82.20214844	89.9887085
3.6	45	69.75	83.3625	90.849375
3.7	46.25	71.109375	84.47128906	91.65331787
3.8	47.5	72.4375	85.5296875	92.40308594
3.9	48.75	73.734375	86.53886719	93.10116943
4	50	75	87.5	93.75

Complete Transmission Flush!

mashley

CroMath

mashley

CroMath

mashley

CroMath

marvinstockman

egads

DrD

Denis

egads

davedrivesody

mashley

mashley

davedrivesody

waveform

DrD

CroMath

Glennda5id

CroMath

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