Safe to flush trans?

[zerosoma]

Hyundai hasn't had a trans flush in roughly 4 years and 40,000 miles. I heard that if you flush a transmission after the oil has been in there too long you risk losing the trans.

I did one partial flush last year where I pumped out a couple quarts and put a couple fresh quarts in. I noticed a rough delayed (by 1 second) shift into drive right after backing out of my driveway this crisp morning. It concerned me. Transmission fluid doesn't smell or look burnt or have particles in it last time I checked. May have overfilled just a touch though.

 

[rrguy]

That doesn't sound like its been too long to me?
I think thats refering closer to vehicles 20 years old with 200,000 miles that never had an trans flush.

 

[Subdued]

Most mfgs recommend against flushes period. Dropping the pan and replacing what comes out every 50k is sufficient.

 

[stchman]

Does your Hyundai have a drain plug on the automatic transmission? If yes, then just drain the fluid out and put the same amount that came back out. Refer to your owners manual for the correct fluid.

 

[Tanama]

Originally Posted By: Subdued
Most mfgs recommend against flushes period. Dropping the pan and replacing what comes out every 50k is sufficient.


The above statement is correct.

 

[RF Overlord]

Originally Posted By: Subdued
Most mfgs recommend against flushes period.
I'm not sure that's true. I think only Honda has a prohibition on the use of fluid exchange machines.

A fluid exchange is Ford's preferred method, according to the service manual for my cars.

 

[Donald]

Originally Posted By: zerosoma
Hyundai hasn't had a trans flush in roughly 4 years and 40,000 miles. I heard that if you flush a transmission after the oil has been in there too long you risk losing the trans.

I did one partial flush last year where I pumped out a couple quarts and put a couple fresh quarts in. I noticed a rough delayed (by 1 second) shift into drive right after backing out of my driveway this crisp morning. It concerned me. Transmission fluid doesn't smell or look burnt or have particles in it last time I checked. May have overfilled just a touch though.


You heard wrong about a flush. And call it a total fluid exchange not a flush. If a transmission has no problems then exchanging all the fluid will cause no problems. Some repair shops may give excuses like that as they do not want to be liable for some half dead transmission someone is trying to bring back to life by changing the ATF.

 

[y_p_w]

What does it really achieve other than a warm fuzzy feeling about getting out as much original fluid as possible? You'd think there's a reason why pretty much every modern automatic transmission will only drain less than 50% of the fluid through taking off a drain bolt and/or dropping the pan. The important thing to do is replenish the additives. That's also the case for a lot of fluids. I took care of a problem with my wife's Civic's power steering whine by simply adding less than 2 oz of OEM PSF. I did a full purge later, but that was more because it made me feel good and probably meant it would stay trouble free longer. However, what's the difference between 40% and 90%?

If it was so important that as much fluid be drained as possible, manufacturer's would have made that possible with a simple drain bolt at the torque converter.

 

[fdcg27]

Does your Hyundai have a "real" (as opposed to brozne mesh) filter and does it have a pan to drop?
It would be wise to drop the pan (if it has one) clean it, especially the magnet and replace the filter.
You can then replace the volume of fluid that drained out and you should be good to go.
Verify the fill level per Hyundai's instructions afterwards.
A flush is not needed, and 40K since your last flush is not long enough to worry about.
IMHO, a transmission that dies after a fluid change is a transmission that would have died without one.
I can't see anything in fresh ATF that would kill a transmission. I'd think that fresh friction modifiers would be a good thing, since that should reduce any clutch pack slip and the detergent adds in ATF are at a pretty low level relative to any motor oil since ATF never has to deal with combustion products.

 

[RF Overlord]

Originally Posted By: fdcg27
IMHO, a transmission that dies after a fluid change is a transmission that would have died without one.
Quoted for truth.

 

[Trav]

Originally Posted By: RF Overlord
Originally Posted By: fdcg27
IMHO, a transmission that dies after a fluid change is a transmission that would have died without one.
Quoted for truth.

+1 Thats a fact.

 

[chad8]

Originally Posted By: zerosoma
Hyundai hasn't had a trans flush in roughly 4 years and 40,000 miles. I heard that if you flush a transmission after the oil has been in there too long you risk losing the trans.

I did one partial flush last year where I pumped out a couple quarts and put a couple fresh quarts in. I noticed a rough delayed (by 1 second) shift into drive right after backing out of my driveway this crisp morning. It concerned me. Transmission fluid doesn't smell or look burnt or have particles in it last time I checked. May have overfilled just a touch though.

You did not perform a flush.you did a partial fluid removal/exchange. That is what modern machines do. They use your transmission pump to exchange all the fluid. This is very beneficial , similar to draining all the oil from your crank case. Would you do a partial oil change?
The most important aspect is using the correct fluid. Do not scrimp. Do not use universal fluids. Do not use friction modifier additives . Newer Hyundai's mostly take
Automatic Transmission Fluid SPH-IV
Specifically formulated for use in certain Hyundai transmissions that require Hyundai Genuine SP-IV ATF.

Provides improved shift performance
Provides corrosion, rust and wear protection
Reduces varnish and sludge build-up

Note: SPH-IV and SP-III are not interchangeable.

Part #: 0023219045
Size: 1 qt
OEM #: 00232-19045 Application: 2009 and later Hyundai/Kia Sonata, Genesis (excludes Coupe), Santa-Fe 3.3L & 3.5L engines

Older ones are less picky and take Mercon.

 

[AP9]

Originally Posted By: y_p_w
If it was so important that as much fluid be drained as possible, manufacturer's would have made that possible with a simple drain bolt at the torque converter.


Then (some) people wouldn't want to ever change their "filters." (Using the term filter loosely here.)

When there is no drain bolt, you have to drop the pan to get fluid out anyway.




And there is always confusion with the term "flush" . . .

Some people use it to refer to a pressurized reverse flow of ATF through the transmission (which could be potentially problematic by dislodging stuff), while others are referring to putting some kind of cleaning solvent through (even riskier), and others simply mean a full fluid exchange (safer bet than the other two, but even so usually not necessary unless the wrong fluid was used or something along those lines).

 

[y_p_w]

Originally Posted By: AP9
Originally Posted By: y_p_w
If it was so important that as much fluid be drained as possible, manufacturer's would have made that possible with a simple drain bolt at the torque converter.


Then (some) people wouldn't want to ever change their "filters." (Using the term filter loosely here.)

When there is no drain bolt, you have to drop the pan to get fluid out anyway.




And there is always confusion with the term "flush" . . .

Some people use it to refer to a pressurized reverse flow of ATF through the transmission (which could be potentially problematic by dislodging stuff), while others are referring to putting some kind of cleaning solvent through (even riskier), and others simply mean a full fluid exchange (safer bet than the other two, but even so usually not necessary unless the wrong fluid was used or something along those lines).

I was referring to a means to drain the fluid from the torque converter. I haven't actually heard of any, except people who drilled their own holes and tapped the threads themselves. The big problem I see with that is then how do you fill the torque converter.

I've done ATF drain and fills before. Super easy on a Honda transmission without a pan, provided you can remove the drain bolt. I couldn't get it off my wife's Civic with a 7" Craftsman ratchet handle, but just bought a 10" flex bar this week. I think that should give me a more solid leverage (the wiggle of the ratchet handle is an issue) and maybe twice the effective length. I also did it on my folks' GM minivan with an AC Delco filter and AC Delco Dexron III fluid. Absolutely hated removing the pan from a Hydra-Matic transmission. The mess was just ridiculous from dropping the pan. I also bought and ATF filter for my dad's Buick, but didn't have any means to get under there.

 

[SteveSRT8]

Originally Posted By: zerosoma
Hyundai hasn't had a trans flush in roughly 4 years and 40,000 miles. I heard that if you flush a transmission after the oil has been in there too long you risk losing the trans.

I did one partial flush last year where I pumped out a couple quarts and put a couple fresh quarts in. I noticed a rough delayed (by 1 second) shift into drive right after backing out of my driveway this crisp morning. It concerned me. Transmission fluid doesn't smell or look burnt or have particles in it last time I checked. May have overfilled just a touch though.


Many modern cars are VERY sensitive to fluid levels. Since they may not have a dipstick you must become familiar with the exact requirements of your particular platform, as even a similar slushbox in a different model may have different specs.

I have searched far and wide in the entire state of Florida and have NEVER seen anything but passive fluid exchange machines anywhere, dealer or indie shop. In most auto trans the valve body has many check valves that simply do not allow any reversed flow of any kind. So no 'flush' if you mean reversed flow.

Dropping the pan is a necessary step in the early life of a slusher as the trans generates most of its debris when new, after that a fluid exchange is an efficient method, especially compared to wasteful pan drops which merely dilute old fluids.

 

[Jim Allen]

fcdg27, RF Overlord, Trav, Chad8, AP9, Steve SRT8... right on!

Some of you are missing the point. There are two reasons to change the fluid, to rid the trans of contamination and to replace depleted oil. In either case, but especially the first, you want to get as much of the old oil out as possible. A passive flush or fluid exchange does that well, whether you use a machine or do it at home with a bucket.

Small D&Fs do that too but they are more effective at replenishing depleted fluid than removing contamination. IMO, a single D&F is useful for maintenance done at (relatively) frequent intervals to both rid the trans of a small amount of contamination and to replenish the additives. If the oil is used up and full of contamination, it's just a drop in the bucket and nigh onto useless. You can do repeat D&F but how many times must you do that to have a meaningful effect? A cooler line or passive flush is so easy on most cars and gets the job done with less waste.

I'll play my Eleftherakis and Khalil card again by pointing out their statistic, based on decades of research and thousands of samples of ATF, that the average automatic generates 75% of it's lifetime amount of contamination in the first 5K miles. That what's built in from manufacturing and from break in. After that, the rate of contamination from wear is relatively low. This makes the first change the most important and if your trans has never had one, the oil is a slurry of manufacturing debris, break-in contamination and normal wear particles. On top of that, the oil may be depleted so the gunk in the oil can potentially cause even more wear than it would with fresher oil.

Bearing the above in mind, if your AT has never had a full fluid exchange (passive flush), that is priority one. On most transmissions, filtration is minimal (no better usually than about >40 um nominal and often no better than >80 um) so the addition of a more efficient external filter essentially eliminates the contamination problem, both with a newish trans with a lot of junk in the oil and an older one that has fully broken in. You can then worry only about fluid depleation.. which is slower with cleaner oil.

So, small volume D&Fs are a useful regular maintenance practice but at some point, every trans should have a full fluid exchange and/or external filtration added (if it doesn't already have it...its becoming more and more prevalent).

 

[Donald]

Originally Posted By: Jim Allen
fcdg27, RF Overlord, Trav, Chad8, AP9, Steve SRT8... right on!

Some of you are missing the point. There are two reasons to change the fluid, to rid the trans of contamination and to replace depleted oil. In either case, but especially the first, you want to get as much of the old oil out as possible. A passive flush or fluid exchange does that well, whether you use a machine or do it at home with a bucket.

Small D&Fs do that too but they are more effective at replenishing depleted fluid than removing contamination. IMO, a single D&F is useful for maintenance done at (relatively) frequent intervals to both rid the trans of a small amount of contamination and to replenish the additives. If the oil is used up and full of contamination, it's just a drop in the bucket and nigh onto useless. You can do repeat D&F but how many times must you do that to have a meaningful effect? A cooler line or passive flush is so easy on most cars and gets the job done with less waste.

I'll play my Eleftherakis and Khalil card again by pointing out their statistic, based on decades of research and thousands of samples of ATF, that the average automatic generates 75% of it's lifetime amount of contamination in the first 5K miles. That what's built in from manufacturing and from break in. After that, the rate of contamination from wear is relatively low. This makes the first change the most important and if your trans has never had one, the oil is a slurry of manufacturing debris, break-in contamination and normal wear particles. On top of that, the oil may be depleted so the gunk in the oil can potentially cause even more wear than it would with fresher oil.

Bearing the above in mind, if your AT has never had a full fluid exchange (passive flush), that is priority one. On most transmissions, filtration is minimal (no better usually than about >40 um nominal and often no better than >80 um) so the addition of a more efficient external filter essentially eliminates the contamination problem, both with a newish trans with a lot of junk in the oil and an older one that has fully broken in. You can then worry only about fluid depleation.. which is slower with cleaner oil.

So, small volume D&Fs are a useful regular maintenance practice but at some point, every trans should have a full fluid exchange and/or external filtration added (if it doesn't already have it...its becoming more and more prevalent).


Would a Magnefine inline filter catch most of the break-in contaminants?

 

[Jim Allen]

Certainly and that's why many transmission shops use them, or the similar filters, after overhauls.

 

[Donald]

Originally Posted By: Jim Allen
Certainly and that's why many transmission shops use them, or the similar filters, after overhauls.


I thought it was to catch any remaining debris from the old transmission failing.

 

[Jim Allen]

Right but that's what it's doing for break-in too, Failure debris, manufacturing (or remanufacturing) debris, break in and normal wear. It catches it all.