Automatic Transmission Flushes: Is it possible that regular and more frequent fluid replacement makes filter replacement unnecessary?

[BonzaiDuck]

It was recently announced after the Suleimani assassination and Iran's response, that the USAF had deployed several B-52 bombers to the island of Diego Garcia in the Indian Ocean. Apparently, the B-52 has been in service now for nearly 65 years. That's the same policy I seem to have with my "used", "ancient" vehicles.

And after 50 years of owning more than a dozen vehicles with some DIY hands-on experience unfamiliar to many owners, I'm humbled at learning certain things late in the game.

I've had only three vehicles with automatic transmissions: a limited edition 64 SS Impala, a 73 Volvo 164, and my current trusty 95 Isuzu Trooper LS. The Chevy tranny had been rebuilt; I never fiddled with the fluid and thought to leave it to a repair-shop as they saw fit. I did not have the car long enough after the rebuild to discover the consequences of "common car-owner negligence" pertaining to the auto transmission. Similarly with the Volvo. Its tranny needed work within 6 months of my purchase, and my experience with the car was so frustrating that I unloaded it within two years.

Then, there's the Trooper. At first, I was taking it to a dealership for service, and didn't think to walk point on service priorities. I wasn't paying much attention to the auto transmission; wasn't checking the dipstick regularly. Worse -- didn't pay attention when the transmission temperature light went on. Soon thereafter, two years and four months after buying the 6-year-old pre-owned Trooper, a marathon trip from CA to VA was interrupted for two dismal rainy days in Kingman, AZ, while a Toyota dealership ordered and installed a remanufactured transmission.

After that, I'd take the Trooper to my repair-shop-owner/mechanic once every year or so and tell him "By the way -- service the transmission -- give it whatever it needs."

The 4L30-E GM transmission was first flushed of Dexron-III 12,000 miles after purchase and installation. It was then flushed successively at 4,000, 5,000, and 6,000 miles thereafter. Subsequent shop orders showed that the mechanic had merely "checked" the transmission -- examining fluid level, color, perhaps its shifting behavior or performance. Since the mileage on the reman transmission is now around 60,000, it has endured about 30,000 miles since the last flush or ATF Dexron-III replacement. The factory shop manual suggests an initial 7,000-mile interval, then 15,000, and every 20,000 after that.

So while the Trooper was lavishly serviced with more ATF flushes than recommended in its first 30,000 miles of use, it has now exceeded factory recommendations by 10,000 miles since the last flush. But a lot of online advice has mechanics suggesting ATF flushes only after 50,000 -- some mentions of 100,000 miles. There is various advice about flushing "old" transmissions, perhaps where the fluid is still at least a light brown color. Flushing old transmissions is not too well recommended after 90,000 miles. It is as though mainstream mechanical wisdom simply assumes that owners would wait until the fluid turns black at that point, to just have the assembly dropped out of the car and rebuilt with new seals and other particulars.

This month, a white paper towel showed the fluid from the dipstick as almost perfectly pink -- with a very narrow amber edge to the stain. And of course, my mechanic told me "No. Doesn't need attention. We'll merely check it next year again."

So I purchased an extraction pump and tubing for about $30, and decided to do it anyway. Easy -- and with preparations, there is no mess. Recycling trips coincide with grocery errands. I spent maybe $100 on new Dexron-III, or about 15 quarts. My mechanic would've charged me a very reasonable $250, although he did his best to discourage it.

The remaining question is the matter of the transmission filter. The shop manual's 100,000-mile chronological service chart and list says nothing about an interval for filter replacement. The beginning section of "4L30-E Automatic Transmission" which deals with routine service mentiions flushing as "fluid replacement" and says "remove the fluid through the dipstick fill-port with a suitable extraction tool. Alternatively, remove the main transmission oil pan, and replace the filter if necessary."

But removing the oil pan doesn't allow replacement of more than 40% of the fluid at a time -- and the same with extraction through the dipstick fill-port. Flushing is iterative: removal of 40% for each iteration leaves 8% of the previous fluid after five iterations.

In other words, if you perform your flush through the dipstick fill-port with a transfer pump, no need to replace the filter; if you do it by dropping the pan, you merely have an opportunity to replace the filter. And dropping the pan requires dropping mid-sections of the exhaust system -- a lot of trouble.

Symptoms of a clogged filter are enumerated on several self-help sites:
-- transmission overheating
-- leaks
-- slipping in gear
-- delay before the car moves when pressing accelerator with gear in Reverse

Of course, I have none of these symptoms. My transmission seems to perform better than it did when I was paying someone else to service it. I used some Blue Devil Tranny Sealer -- 1/3 the recommended amount -- to stop a small leak at the torque-converter main seal. Removing the BD (to avoid actual damage to the seals) was a reason I went against my mechanic's advice and chose to flush the transmission anyway.

Filter replacement would be called for particularly when a flush has been performed on a transmission with degraded fluid. Dexron-III ATF is described as a good solvent, recommended for use in an ENGINE flush in combination with engine oil, just as you might use a quart of Marvel Mystery Oil, and MMO looks a lot like Dexron cherry-juice. So on an old transmission, the flush may not only dissolve varnish build-up inside the transmission from "old ATF", but it might dislodge larger particles of it -- clogging the filter.

I'm wondering if more frequent ATF replacement (flushing) would eliminate a need to ever replace the filter. The filter is a $40 item. But dropping the exhaust and main oil pan is a major undertaking. I would think there might be a good opportunity to replace the Y-shaped intermediate or center exhaust pipe and the Oxygen sensor that is screwed into it -- parts cost of about $160. But then, why do that if there's nothing wrong with the parts -- provided the transmission filter doesn't need replacing anyway?

 

[ISAslot]

Interestingly, my C6 ford transmission doesn't really have a 'filter' it's more like a screen. It's not something that would ever get clogged.

 

[ISAslot]

As for the topic question, I would think this would have to do with the type of filter. If it can clog then it should be replaced.
I wouldn't flush or replace the fluid more than recommended. As long as the fluid is in spec it should be fine.
The friction material will gradually increase, however it tends to stay in the bottom of the pan in my experience. There will be some in other areas where I can accumulate like in band servos. Regardless, I can't see a flush removing much of it. I would just replace the majority of the fluid at the recommend interval.

 

[BonzaiDuck]

As for the topic question, I would think this would have to do with the type of filter. If it can clog then it should be replaced.
I wouldn't flush or replace the fluid more than recommended. As long as the fluid is in spec it should be fine.
The friction material will gradually increase, however it tends to stay in the bottom of the pan in my experience. There will be some in other areas where I can accumulate like in band servos. Regardless, I can't see a flush removing much of it. I would just replace the majority of the fluid at the recommend interval.

Sure -- "If it can clog then it should be replaced." But the factory manual has no recommended interval for replacement! It would just seem to me that one would then replace it if the tranny exhibited symptoms of clogging.

By "friction material", do you mean particles of varnish? Or particles of friction plates? I'm sure all of those things eventually wear out, just like the friction plate of a manual transmission. But given the way the SUV has been driven since the transmission replacement over the mere 60,000 miles, I'd say those parts would have a long way to go. Of course, as you say, particles might accumulate in the bottom of the pan, even as we might imagine them reaching the filter.

I suspect that owner-drivers such as myself are subject to a "placebo effect" -- that is, we imagine there is some improvement for doing something, even if there really isn't. But I could definitely sense a change in transmission operation for the better a day or two after the Blue Devil was added, and then a change for the better after the entire capacity of fluid was replaced. First, an occasional "clunk" between 3rd and 4th as described about the 4L30-E as a "design flaw" disappeared, even as I could still hear a click between gear changes; then, those sounds seemed to totally disappear. It just shifts more smoothly. Doesn't seem to slip or anything. No indication of the symptoms describing a clogged filter . . .

So I suppose I can just wait another 20,000 miles -- unless, of course, I encounter any trouble with the transmission . . . .

I'm just a bit amazed at how easy fluid replacement (or call it "flushing") is, or to think that I'd always assumed I had to get a mechanic to do it. Howsoever long they may last, the manual transfer pump makes the job clean and easy.

 

[BonzaiDuck]

Interestingly, my C6 ford transmission doesn't really have a 'filter' it's more like a screen. It's not something that would ever get clogged.

As I understand it, some filters are fabricated with a felt-like material or something like cloth. I can't get a sense of it just looking at pictures of my Trooper tranny filter:

Now that I look at it for purposes of this thread and post, there are two filters:
An In-line filter kit with a magnetic component

and a "Shallow pan" filter in a kit with a pan-gasket

I can go back to the factory manual pages to get a better idea, but it seems the latter filter is the one mentioned as a "target of opportunity" when removing the pan. I can only speculate that the cutout areas of the metal plate are covered with screen material**. As much as the magnetic filter's manufacturer promo suggests regular replacement, the factory manual doesn't seem to indicate it. The factory manual would say something in the maintenance schedule about it if it were warranted. Maybe someone else has some insights about this.

Repair shops and mechanics tend to slide on these things until something actually goes wrong. I've personally never had an automatic transmission over the span of 60,000 miles, but I would guess that's only half a life-cycle.

For maintenance, however, it seems a bit of a stretch to assume that dropping the exhaust just to drop the pan is "routine". Anybody else know about this stuff?

UPDATE: I scanned through the factory manual again. The section on "fluid replacement" only says the fluid should be replaced under harsh driving conditions or indications that it is starting to turn "brown", although it is nevertheless recommended for every 20,000 miles after the initial more frequent replacement intervals. There is no recommendation to change the filter.

Further -- the "in-line" filter is not indicated or shown in any of the diagrams -- only the "shallow pan" filter is shown. And again, no replacement interval, and you come away with the sense that it would only be replaced when dropping the main tranny oil pan to perform other types of service.

UPDATE to UPDATE: These inline filters from ATP, Raybestos and Magnefine are additions or enhancements to be installed at the transmission cooling lines. Mixed reviews. Preference is for those with a metal cannister or chamber. They would only add resistance to the flow of ATF through the cooling lines. Other indications from information about these particular filters: an interval for normal OEM " shallow-pan filter replacement may be 100,000 miles.

AND! ADDENDUM: Here is an interesting article responding to the question "When or how do automatic transmissions wear out?"

Why Does an Automatic Transmission Wear Out?

So I guess one would expect a need for a rebuild or tranny replacement at about 120,000 miles. I don't know the six-year repair history prior to when I bought my Trooper, but the transmission was smoking and dead at about 120,000. If I had focused some service on it when I bought the car at 96,000 miles, I can only guess.

** There is one area of this shallow-pan filter -- a rounded rectangle -- that could be some sort of felt material of a light yellowish color.

 

[sdifox]

there is no unclogging filters. So you can extend the life, but that is not infinite.

 

[dave_the_nerd]

Theoretically, yes, fresher fluid would result in slower wear and less junk (tiny bits of metal) getting caught in the filter, which should extend its life. In the case of my car (2012 Acura TL), the recommendation is for partial fluid changes every 30k and a filter replacement at 120k. (IIRC)

So yeah, maybe if I replace fluid more frequently, I'd get the filter to last longer. But cost-wise, it doesn't make a lot of financial sense to replace expensive (~$12/qt) fluid more frequently just to eke another few miles out of a $35 filter. Hell, if I were the paranoid type, I might just replace the filter more frequently out of principle.

It also depends on what filter type you have. If it's a permanent mesh filter, there's no replacement needed anyway. If it's a filter that's supposed to be replaced every time you change the fluid, it's probably not doing your transmission any favors to skip that, even with fresh fluid.

 

[BonzaiDuck]

Theoretically, yes, fresher fluid would result in slower wear and less junk (tiny bits of metal) getting caught in the filter, which should extend its life. In the case of my car (2012 Acura TL), the recommendation is for partial fluid changes every 30k and a filter replacement at 120k. (IIRC)

So yeah, maybe if I replace fluid more frequently, I'd get the filter to last longer. But cost-wise, it doesn't make a lot of financial sense to replace expensive (~$12/qt) fluid more frequently just to eke another few miles out of a $35 filter. Hell, if I were the paranoid type, I might just replace the filter more frequently out of principle.

It also depends on what filter type you have. If it's a permanent mesh filter, there's no replacement needed anyway. If it's a filter that's supposed to be replaced every time you change the fluid, it's probably not doing your transmission any favors to skip that, even with fresh fluid.

I apologize for my prolix posts, which will try the reader's patience and make it more likely he/she will miss some things.

But as I'd said, to replace my 4L30-E tranny filter, I (or have my mechanic do it) have to drop the exhaust assembly just to access the main tranny oil pan to reach the filter. That's why I'm exploring these issues. Maybe the filter is (lemme see a minute . . . umm . . Rockauto . . ) . . OK . . about $25 for a WIX or Hastings. Once the oil pan is removed, it's just a matter of removing three bolts or so and "Voila!" -- pop in the new filter, tighten the bolts -- done. But "not so done" -- install a new pan gasket and sealer, tighten the bolts securing the pan -- again, not a lot of trouble . . . but then . . . you have to secure the exhaust system. Maybe that's a lot less trouble than I imagine -- can't say.

Exhaust parts are rusty, dirty and trouble sometimes to unhinge. Or, you damage them in their aged state of wear. Perhaps an opportunity to replace a catalytic converter? Something to consider.

But if the recommended interval for filter replacement is 100,000 miles (not even shown as an item for periodic service in my factory manual), I've got 40,000 miles before I need to even think about it -- provided the tranny continues to work properly.

Eventually I can see that friction plates wear out or other things cause trouble. But the way the SUV runs and the transmission behaves now (after a total fluid change), I can see that I'll likely reach that 40,000-mile point before any difficulty.

In fact, I could die before my transmission does -- at 3,000 miles per year. I just like to "plan stuff". The Trooper is my B-52 being retrofitted for backup camera, GPS, LED fog lights and other stuff that demonstrates my pride in it!

Next step is to replace the oil in the transfer case and the gear oil in the front and rear differential/axles. Not a lot of trouble, except I have to lay down on the garage floor and be careful about making messes . . . I've got two quarts of EDGE 5W-40 and four quarts of Valvoline 75W-140 just waiting . . . I keep saying to myself "Manana! Manana!" Well, tomorrow I think I'll do the transfer case. One thing at a time . . .

Then . . . drive that sucker! The 3.2L SOHC Trooper doesn't have a reputation for "muscle". My cousin -- a mechanic -- called it the "Pooper". But it's a sweet ride!

 

[tweaker2]

There's also this other idea to deal with re: auto trannies:

If a car's auto trans fluid hasn't been changed after many years of driving, then in some situations changing the fluid may actually worsen the tranny's job of transferring power to the wheels in that friction particles floating in the oil may have been aiding the clutches toward keeping a grip. Once those particles are gone through oil change clutch slippage may get bad enough that an overhaul is necessary.

This is of course a worst case scenario. I've not personally experienced this myself yet I've run into this problem being mentioned on those car/truck forums that I frequent often enough that I think it's a plausible reason to consider.

So with that, whenever I'm asked to help friends/relatives buy a used car, if when checking the tranny oil in a car I see that the oil is dark, smelly, etc. and the car is more than ten years old with high mileage I assume the oil has never been changed and keep in mind that changing the tranny oil might make things worse than better.

It's a coin flip/luck of the draw kind of thing, but I think it's worth keeping in mind.

 

[BonzaiDuck]

There's also this other idea to deal with re: auto trannies:

If a car's auto trans fluid hasn't been changed after many years of driving, then in some situations changing the fluid may actually worsen the tranny's job of transferring power to the wheels in that friction particles floating in the oil may have been aiding the clutches toward keeping a grip. Once those particles are gone through oil change clutch slippage may get bad enough that an overhaul is necessary.

This is of course a worst case scenario. I've not personally experienced this myself yet I've run into this problem being mentioned on those car/truck forums that I frequent often enough that I think it's a plausible reason to consider.

So with that, whenever I'm asked to help friends/relatives buy a used car, if when checking the tranny oil in a car I see that the oil is dark, smelly, etc. and the car is more than ten years old with high mileage I assume the oil has never been changed and keep in mind that changing the tranny oil might make things worse than better.

It's a coin flip/luck of the draw kind of thing, but I think it's worth keeping in mind.

Yes -- those considerations concerned me as I pursued my choice to flush. Like I said, it had been flushed at 12,000, 4,000, 6,000, 5,000 intervals, and this DIY flush occurred after 40,000 since the last ending the 5,000-mile interval.

I haven't noticed any slipping; Reverse engages immediately when pressing the accelerator slightly. Any overheating would be reported through the "Auto Trans Temp Warning" light, and it only flashes through its initialization at start-up. So there's no indication that the filter begs changing, and there doesn't seem to be any degradation in performance. If I re-visit changing the tranny filter at 100,000 (tranny) miles, it could be ten years from now. I could be dead by then. I'd hope that with equal and reasonable maintenance between now and then (if the DMV and my eyesight allow me to continue driving), I could figure on re-building the tranny at between 110,000 and 120,000 miles.

But my annual mileage on the vehicle has been less than 4,000 miles/year for at least the last ten years.

If I were buying another used car with mileage over 80,000, I'd probably focus my attention immediately on an automatic transmission. I don't think mainstream owners and drivers pay enough attention to auto-trans maintenance. That's what happened to me when I bought my Trooper in 2002, not paying attention to fluid-level or the AT Temp Warning light until the tranny burned out and died during a cross-country journey.

 

[skyking]

If it's a true filter, then no. I would always opt for a new filter.

 

[BonzaiDuck]

If it's a true filter, then no. I would always opt for a new filter.

Like I said -- there's no spec filter change interval in the factory manual, but general forum/web-site indications seem to indicate it would be done at 100,000 miles. And again -- you have to drop the whole exhaust and then the main tranny oil-pan to make the change. Everything else in the chronological maintenance schedule of the factory manual is accounted for.

The filter assembly for the 92 to 97 automatic Troopers with 4L30-E transmission are shown in this RockAuto link:

Transmission Filter

Both from looks of it and as I recall, there are three possibly 10mm (flat-to-flat) retaining bolts or screws. But the whole tranny oil pan has to come off, then be replaced by a new gasket and sealer -- after the exhaust assembly at the cat converter has been dropped. They didn't design the SUV and its transmission for frequent pan-gasket and filter changes.

 

[skyking]

If you are concerned about it, change it now and never worry about it again. I've replaced 2 autos on my cummins-powered trucks, and the cost and hassle from those experiences will always push me to doing the proper maintenance.

 

[BonzaiDuck]

If you are concerned about it, change it now and never worry about it again. I've replaced 2 autos on my cummins-powered trucks, and the cost and hassle from those experiences will always push me to doing the proper maintenance.

The $2,500 replacement and 3-day stopover in Kingman AZ during 2004 weighed similarly on my mind ever since, so at 60,000+ miles, the tranny had been flushed some four times before the 40,000-mile interval prior to the one I performed last week. My mechanic/shop-owner, examining the fluid spot on a white napkin, discouraged it as totally unnecessary. I mentioned the filter change complicated by dropping the exhaust and oil pan, and he dismissed that prospect as just as unnecessary. The factory manual maintenance schedule is two pages long, covering everything to include engine air-filter, the axle/differential and transfer-case oil changes, wheel-bearings -- everything -- but no mention of the tranny filter over 100,000 miles.

Web-search points to 100,000 miles without specification of make or model. Lifespan speculations on auto trannies seems to create an expectation of 120,000 give or take. The episode in 2004 occurred at 122,000, but then I'd also been neglectful of the A/T oil temperature light and the sort of attention I'd given the new tranny since then.

I've also located the parts for the exhaust, thinking that I could also change out the intermediate "Y" pipe and oxygen sensor if I were to go through the steps to swap out the tranny filter. I'm still thinking to acquire the parts for less than $200 while they're still available.

But it will be at least five more years before the transmission itself has 80,000 miles of use and wear, and there's absolutely nothing to suggest that there is any obstruction or clogging of the filter. So I'm going to let it slide.

 

[skyking]

Oh you're not letting it slide. You just worry about things way ahead of time I would change the filter at the hundred thousand miles, and then you get to look very carefully at that filter element and see just how your transmission is doing it's valuable information.

 

[BonzaiDuck]

Oh you're not letting it slide. You just worry about things way ahead of time I would change the filter at the hundred thousand miles, and then you get to look very carefully at that filter element and see just how your transmission is doing it's valuable information.

Yes! We're on the same page here! Like I said, I never paid much attention to the auto-tranny vehicles I'd driven for transmission maintenance, thinking to let the repair shop and mechanic do it. This summer, I had an experience for the potential purpose of Yelp that I would entitle "The Little Repair-shop of Horrors and its Mechanic from Hell". So whether it's "worry", sage "planning" or a combination of both, it's true -- that's what I'm doing now.

I'm just glad that the Trooper survived my casual attitude about paid-for service. And "valuable information"? -- certainly! I have all my detailed smog-test results going back to 2002, no less!

 

[Migs43]

U can clean a trany filter. Use disk brake cleaner.