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Is it true that changing automatic transmission fluid in a high mileage vehicle can ruin the transmission?

This is something that I have often heard: "On higher mileage vehicles the transmission fluid is saturated with friction material from the clutches. Replacing this fluid with new fluid which contains new detergents can start the so called break-in process all over causing more clutch wear. So if you have an older car that is not leaking or consuming transmission fluid just leave it alone." If this is the case then what is the best way to deal with this? Do you change half the fluid (leaving half new half old) along with the filter and gasket?

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  • 1 decade ago
    Favorite Answer

    Just change the fluid as described in the owner's manual. The phrase is changing the fluid on OLDER vehicles. Older transmissions used mineral oil or Dextron (1). When used for long periods of time, they left a varnish coating in the oil passages. New fluid would break the varnish off where it would lodge in the shift valves causing problems. It did not help that when GM released the TH400, they said the fluid was good for 100,000 miles. Causing people to wait 10 years before changing the fluid. Most cars on the road use Dextron-II or better. This does not have the varnish problems unless you have repeat transmission overheating (towing). Some cars (Honda?) don't even have tranny filters any more.

    (a couple of side notes:) The fluid has multiple jobs, lubricating, cooling, hydraulic controls, cushion the shift changes, transfer power in the torque converter, and transferring power in the clutch packs. All trannys wear metal. It is found as the silver sludge in the pan that the repair shop shows you when telling you that you need a rebuild. Sludge (not broken parts) is normal The metal actually washes down into the pan, the filter stops it from being sucked back into the system. The metal is from the steel pressure plates of the clutches and drum metal, not the "friction material". The friction material is PAPER !, which holds the fluid between the plates.

  • Anonymous
    5 years ago

    For the best answers, search on this site https://shorturl.im/aviw6

    Yes, if you haven't serviced it on a regular basis, doing so now could actually cause it to start slipping. Especially if you flush it. If the transmission is already damaged, those metal shavings and other debris is providing the friction to keep it working. If you flush that fluid out and put in new fluid, there might not be enough friction to work anymore. Draining it and refilling it might not be as bad though. It depends on the amount of damage. But if you drain it and check out the fluid, you will get a better idea. Since just draining it doesn't remove all of the fluid, if there is damage, the old fluid that still remaining in the converter might be enough to keep it working. Kind of like a fish tank, you leave a little of the old water in there for the algae and bacteria the fish need. The inside of the transmission is worn and damaged, it needs the friction at this point. But if there is damage, at one point or another you will need to replace or rebuild the transmission. It wont matter how much friction you have if everything is broken and worn down to nothing. But replacing the fluid really isn't going to help at this point, as far as keeping the transmission in good shape. That's why a transmission service is called "preventive" maintenance. And no, the transmission doesn't get "used" to the old fluid. New fluid is better for the transmission and will prolong the life, however if the transmission is already damaged, the friction provided by the old fluid (and all the debris in it) is what is keeping it from slipping, for now. It will eventually completely tear up the tranny and it will need to be fixed. But changing the fluid at this point could very well cause it to start slipping. The best thing would have been proper maintenance in the first place... We can all agree to that. At this point, I think your best option is draining out some of the old fluid and adding new. Flushing would completely remove all of the old fluid, so just drain it instead. You will be able to inspect the old fluid for debris and see how bad it is. Contact any reputable tranny shop and ask them if they will flush your transmission fluid. Then tell them you have 150k + miles and have never serviced it before. 99% of them will tell you no, and why. Then again, some will tell you sure, because they know you will be forced into getting a rebuild right after the service.

  • Anonymous
    4 years ago

    1

  • 1 decade ago

    I am sure you have heard the saying, if it isn't broke, don't fix it. And, the same holds true, for a automatic transmission... If the transmission is working fine, the way it is, you are best off, leaving it be. Just stick to the normal business, of checking the fluid level, now and again. You need not worry, unless you see or feel a marked change in the transmission. If this arises, then, check into the problem, but not untill. If all is going smoothly, leave it be, till something goes wrong.

    Source(s): I know several people, with older cars, that had their transmission fluid replaced, and, once the fluid was replaced, all he** broke loose. All the transmissions worked fine, till the fluid change, now, they have nothing but problems. In fact, I have a 1979 Dodge R/T, with a automatic transmission, and, the fluid, has never been replaced, in the car. (Only checked and added to bring the level to normal). And, it still works, today. The car is about ready to fall appart from so much rust, but the transmission is still good.
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  • 6 years ago

    This Site Might Help You.

    RE:

    Is it true that changing automatic transmission fluid in a high mileage vehicle can ruin the transmission?

    This is something that I have often heard: "On higher mileage vehicles the transmission fluid is saturated with friction material from the clutches. Replacing this fluid with new fluid which contains new detergents can start the so called break-in process all over causing more clutch wear. So...

    Source(s): true changing automatic transmission fluid high mileage vehicle ruin transmission: https://shortly.im/rrd61
  • 5 years ago

    2

    Source(s): Vehicle History Search Database - http://vin.trustdd.com/?LAwg
  • 1 decade ago

    Daily maint. is the key to a long life of the transmission.I did both. I didn't change it because I waited to long and I also changed it. My Chevy truck had the turbo 300. They say that if you change it after sitting in the transmission that you flush out lose shavings of the transmission. Some trans have a magnet on the oil pan to catch such shavings. It is your call. But be sure they change the filter and gasket and also drain out the toque converter.

  • 6 years ago

    Yes. It s true. I have a Maxima with 185k and the transmission oil hasn t been changed in 13 years. That is because when mechanics looked at the oil over the years for discoloration or a burnt odor it wasn t found. I have asked many mechanics if I should consider changing it now. They all said absolutely "no". Even at a Nissan dealership a head mechanic said changing it now is risky.

  • 1 decade ago

    Excellent question, but I wish I had the answer, I heard the same story from a mechanic. I had a car with 80K and changed the fluid and 2 months later the tranny went bad. Is that the fluid change or just an old car?.

  • 4 years ago

    3

    Source(s): Vehicle Complete Record http://vinnumberlookup.gelaf.info/?I6dz
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