ATF Fluid exchange machine not a true "flush"?

[oldsohc]

A old friend of mine opened up an automotive shop. I have about 30,000 miles on my Nissan and figure I should do a ATF flush, and was always curious how the exchange machines worked so I brought in. About 8 liters of new ATF was put in the machine, tranny line was undone at the cooler, and the machine hooked up in line, started the car, and began the exchange process.

After the service was done I started to think though. The tranny oil pan was never drained before the service. So when the exchange process began, the fresh fluid going back into the tranny was being dumped back in a pan of old ATF and mixing with it. Upon further investigation and some phone calls around town, this seems to be how most places flush the tranny.

Also on a second note is it true that the fluid that goes through the valves gets dumped back in the oil pan without even reaching the cooler lines?

It seems like using an exchanger is not much more effective than doing a drain and fill a few times as the new fluid gets contaminated anyways?

 

[Johnny2Bad]

Any transmission oil service in my opinion should include replacing the filter, which means dropping the pan and cleaning the pan.

Then after you add ATF through the dipstick (service manual should say how much) the pickup is taking clean oil from the pan. At that point I don't think it matters how you do the flush (manually or with the machine).

If manually you open the fitting at the trans cooler inlet, and keep adding ATF until the fluid appears new; reconnect the lines; re-check and correct if necessary the fluid level via the dipstick, and you're done.

What happens after you button up the pan is the filter holds back any contaminants in the old fluid. In that respect the "new" filter starts life off with particles contaminating it.

I can see why they use the machine as the filter does the very same thing. But it's an old filter.

Also in either case the trans cooler still has old oil in it, which will get mixed into the new fluid at the pan.

But I think it's necessary to do it that way because the return line from the cooler probably has a check valve or thermostatic valve, so a flush isn't possible from that side of the cooler.

In a transmission that hasn't been abused (overheated) I think it should be OK. It seems to me there is no way to insure some old ATF isn't retained, but it should be fine if the trans is fine.

I can give you the short answer:
Replacing an AT filter is slow and messy. Avoiding that is fast and clean. Plus you charge about the same with less labour involved, so the shop definitely sees the upside. Maybe not the customer, though.

 

[SteveSRT8]

absolutely correct. All the machine provides is a cool looking cabinet and a ton of fittings to allow it to be used on almost any car or truck.

The fluid is following the exact same paths it does during operation, the machine does nothing but hold fluids in separate containers.

Note that the overwhelming majority of a slushbox's debris is produced during break in and at low miles. After that there won't be much junk. So a filter change is a big deal at lower mileages, I like to alternate pan drops/filter changes with fluid exchanges.

A bucket works just as well!

 

[229]

Some manufacturer's say do not use a flush machine that uses compressed air because it will stir up gravity laden debris back into the valve body and solenoids. Honda's do not use a serviceable filter and Toyota uses a screen. If there is a mesh filter the best thing to do is replace it and exchange all the fluid with OEM fluid.

 

[RF Overlord]

The way a fluid exchange machine works is as follows:

The machine is charged with fresh fluid into a double-ended cylinder, with a piston and seal at one end. The machine is then connected in series with a cooler line. When the car's engine is started, the transmission's own pump pushes the old fluid into the "empty" end of the machine's cylinder, which causes the sealed piston to push the fresh fluid back into the transmission at the same rate and pressure as would happen under normal driving. There is no mixing of the old and new fluid. Assuming the machine is charged with sufficient fresh fluid, all of the old fluid should be exchanged for new.

Originally Posted By: SteveSRT8
Note that the overwhelming majority of a slushbox's debris is produced during break in and at low miles. After that there won't be much junk. So a filter change is a big deal at lower mileages,
Agreed. Whether you do a fluid exchange or a simple drain & fill, the first filter change is the most important. After the first 10-15,000 miles from new, the transmission produces so little debris that changing the filter isn't necessary for routine maintenance. Having fresh fluid is more important than changing the filter...

 

[Donald]

Originally Posted By: Boosted240
A old friend of mine opened up an automotive shop. I have about 30,000 miles on my Nissan and figure I should do a ATF flush, and was always curious how the exchange machines worked so I brought in. About 8 liters of new ATF was put in the machine, tranny line was undone at the cooler, and the machine hooked up in line, started the car, and began the exchange process.

After the service was done I started to think though. The tranny oil pan was never drained before the service. So when the exchange process began, the fresh fluid going back into the tranny was being dumped back in a pan of old ATF and mixing with it. Upon further investigation and some phone calls around town, this seems to be how most places flush the tranny.

Also on a second note is it true that the fluid that goes through the valves gets dumped back in the oil pan without even reaching the cooler lines?

It seems like using an exchanger is not much more effective than doing a drain and fill a few times as the new fluid gets contaminated anyways?


What you say is true. A good flush should start with dealing with the fluid in the pan before the vehicle is started. Drain via drain plug, drop the pan or extract via dipstick tube. Then refill and start the engine and flush machine. Lots of extra ATF used for the flush will overcome that issue but if you are using expensive synthetic ATF, thats an expensive way to deal with it.

 

[Jiblet]

There is no way to avoid some mixing short of dropping the transmission. Too many galleries, it's not a straight shot like bleeding brakes.

 

[stephen9666]

Originally Posted By: Jiblet
There is no way to avoid some mixing short of dropping the transmission. Too many galleries, it's not a straight shot like bleeding brakes.


+1

No method will get 100% of the fluid out. Just like no oil change will get 100% of the fluid out.

I would guess an exchange will be more effective at replacing most of the fluid than one or even a couple pan drops. And, it will be far less messy.

Especially if it's a vehicle with a screen instead of a true filter, I would have no problem going with just a fluid exchange and calling it good.

An example, my brother's 1995 Ford Escort. I was going to be working on the trans so I bought a new "filter" for it. When I looked at it, it was just a screen, not a true filter. A fine screen, yes, but still just a screen.

 

[The Critic]

The BG propaganda used to say that the difference between a "flush" and a "fluid exchange" is that a flush involves adding cleaning and conditioning chemicals, while a fluid exchange does not - and is therefore useless.

 

[SteveSRT8]

Originally Posted By: The Critic
The BG propaganda used to say that the difference between a "flush" and a "fluid exchange" is that a flush involves adding cleaning and conditioning chemicals, while a fluid exchange does not - and is therefore useless.

I actually used to use one of their machines I bought at an auction cheap. Upon close inspection it was a bladder and a container in a nice cabinet with a pretty sight glass to watch the fluid change colors through. The only items of any value were the huge pile of fittings to adapt to almost any vehicle.

Actually B&G is a good brand, but we all know what happens eventually when you add a 'universal' additive to every slushbox you service...

 

[Vikas]

Aren't most of the professional auto maintenance fancy box machines are like that? Even 3M on car fuel injector cleaning machine is nothing but bunch of adapters, a metal bottle with shop air hookup. They charge a pretty penny not only for that setup but also for the replacement chemicals.

 

[babyivan]

Doing a pan drop is crucial after the initial break-in to change the filter and get the sludge out of the pan, like another poster mentioned.

After that is done, I like the idea of adding a drain plug to the trans. pan.

And at every other oil change, do a drain and fill. This only gets what is in the pan, but since you're doing it every 6K, the fluid will always maintain some level of freshness.

A nice, clean and easy way to keep your trans in good shape for years to come!

Of course, this applies to cars that don't already have a trans. pan drain plug, which I think some imports do have.

I would still do the filter at the OEM recommended intervals on top of this.

 

[Kiwi_ME]

At 30,000 miles that's early enough to do nothing but drain and fills every further 30k. You should never need to pull the pan or change the screen. So, do that next time yourself and save the money. I'd bet it's sparkling-clean inside now.

Very little fluid goes through the valve body compared with the torque convertor and it will have a tiny button filter to get the fine stuff out not caught by the screen.

 

[SteveSRT8]

Originally Posted By: Vikas
Aren't most of the professional auto maintenance fancy box machines are like that? Even 3M on car fuel injector cleaning machine is nothing but bunch of adapters, a metal bottle with shop air hookup. They charge a pretty penny not only for that setup but also for the replacement chemicals.


EXACTLY!

Completely marketing, very little substance involved...

 

[229]

"ATF Fluid exchange machine not a true "flush"?"

Correct. You can do a fluid exchange with the lines off. A flush involves a machine with compressed air that does not require you to operate the vehicles engine. This is the harmful one as it shocks the system with more pressure than the transmission does naturally. This moves particles around but not all of them escape the transmission. Some manufacturers will void your warranty with air flush machine service if they can prove it. A receipt helps them to prove it.