Change AT fluid question

Discussion in 'General Motoring' started by Dan Chirica, Jan 22, 2004.

  1. Dan Chirica

    Dan Chirica Guest

    Hey Guys:

    Is this a good idea? I want to change the AT fluid with synthetic
    (Mobil1). I know if I drain the fluid myself only a fraction of the
    total will drain. I was thinking to replace it (partially) with
    synthetic an repeat the process several time until, hopefully, the AT
    fluid is mostly synthetic.

    Also is there a synthetic differential oil? What good brands of
    synthetic At fluid and diff. oil are there?

    Thanks. Sincerely,

    PS: I apologize if this subject has been discussed before I couldn't
    find any references, though.
    Dan Chirica, Jan 22, 2004
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  2. Dan Chirica

    Edward Hayes Guest

    I use Mobil1 synthetic in both my differentials and in my AT with excellent
    results for 62,000 present miles. For the auto which holds 9.8 quarts your
    first drain/refill of ~ 4.2 quarts will change ~ 1/2 the total. I change
    mine three times driving ~ 1-200 miles between each change. This will give
    you about 95% new fluid. I then change only one drain/refill every 10-15,000
    miles. eddie
    Edward Hayes, Jan 22, 2004
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  3. Why not let the transmission pump it out for you?

    Disconnect BOTH trans lines going to the radiator.
    Do both. Depending on the type of car, the pressure
    side could be the top or bottom fitting on the radiator

    Run some flexible hose from these to an adequate
    bucket to catch the used fluid. Make sure that the
    hoses are toward the top of the bucket. You don't
    want to start sucking the used fluid back into the

    Start car and let it idle. The pump in the trans will
    empty most of the fluid into the bucket for you.

    Make sure you STOP the engine AS SOON AS
    the fluid slows to a trickle. You don't want to run
    it long without fluid.

    Measure the amount of fluid in the bucket. This is
    how much you need to replace.

    Re-connect the trans lines to the radiator and fill the
    trans with the same amount you collected in the

    Start engine, run trans thu all gears, and check level and
    for leaks, and your done.

    Anybody have an easier way?
    Skweezieweezie, Jan 23, 2004
  4. Thats the basics, but a couple comments. Drain as much ATF as you can
    first. This will get the mud out of the bottom of the tranny (do it while
    the ATF is hot). Measure how much you removed. Replace the plug. Add two
    quarts of fresh ATF and start the car. Leave it in Park and watch the ATF
    get pumped into your container. As soon as you see air bubbles, turn off
    the car. Measure how much you pumped out. Add two more quarts and start
    the car again. Keep repeating this process until the fluid getting pumped
    out is nice and clean. Keep track of how much you've added and how much you
    drained/pumped out. Reconnect the cooler hoses and add as much ATF as is
    necessary to equal what you removed.

    You will use 4-6 extra quarts of ATF this way, but it will be clean.

    Fred Flintstone, Jan 23, 2004
  5. How good can it be to run the tranny with little or no fluid?
    David Henderson, Jan 24, 2004
  6. Dan Chirica

    Edward Hayes Guest

    I drain and refill mine 3X times (drain plug) to achieve ~ 95 % new fluid, I
    drive several miles between each of the 3X changes so the new gets mixed. I
    hesitate to remove hoses and clamps for a flush as it can introduce leaks
    later on. I use a new sealing washer on the final drain/refill. Eddie
    Edward Hayes, Jan 24, 2004
  7. I tend to agree with Eddie's philosophy and use this approach on 97 Legacy,
    but now I am planning to switch to synthetic ATF on WRX and mixing new
    synth and old dino does not seem right. On other hand, wasting 4-6 quarts of
    synthetic at $8/quart by pumping it until 100% new is excessive!
    Any suggestions about switching to synthetic ATF without cross-contamination
    and wasting 4-6 quarts?
    David Spektor, Jan 24, 2004
  8. Two things:

    1. What is the millage? If this is the first change and the
    tranny has a large amount of miles on it (being a 97, I'm guessing
    that it's pushing 100K if not past it already), then you may wish to
    think twice about changing/flushing your transmission. A problem that
    is sometimes encountered in performing the first drain/flush on a
    transmission with high millage is that crud that has natrually built
    up in the transmission will be dislodged from a semi-harmless place in
    the transmission and proceed to travel to where it can impeed fluid
    flow and/or cause wear or other issues with various AT parts. You can
    search around on Google for cases of this and warnings of this and
    determine if the proceedure is worth it to you.

    2. Automatic transmission fluid does much more than any other
    fluid in your vehicle. The fluid serves three purposes: Hydraulic
    drive/shift control, general lubrication, and cooling. Thus allowing
    the transmission to run with low fluid or without fluid is akin to
    running your engine without oil, coolant, and your power steering
    without fluid all at the same time. Needless to say, in that
    situation, more damage will be done than any good you were trying to
    do. Most synthetics are compatible with dino fluids, so the first
    suggestion of drain, add, drive, and start the whole process over
    again is a safe suggestion. Synthetic typically has a "cleaning
    power" above and beyond normal dino fluid. So in doing the
    drain/fill/drive routine over the course of a couple of weeks or so
    will give you a chance to get some of the crud and other things that
    may have been "cleaned" off of parts out of the transmission in the
    process. If you must use the flushing method, then use this process.
    Take TWO buckets. Make sure one of them is clean enough to eat off
    of. Fill the clean one with the new fluid you are wanting in your
    transmission. Be sure to put more in the bucket than your
    transmission will need (two extra quarts is a good saftey measure.
    Disconnect the fluid ouput hose (the line that carries the fluid from
    your tranny to the cooler) from your transmission cooler input and
    place it into the empty bucket for the old fluid. Disconnect the
    return line from the transmission cooler (the line that carries the
    fluid back to the transmission) and rig a piece of hose long enough to
    reach the bottom of your bucket with new fluid. How you rig this
    isn't important, but make sure it's a tight fit and will allow a
    consistant flow of new fluid into the tranny. By now you can probably
    see that it's a two person job. Once you have things set up and have
    checked everything, have the second person make sure the car is in
    neutral (wheels blocked of course for saftey). Then have them start
    the car. Allow the old fluid to be pumped out and the new fluid
    pumped in to replace it. Stop the car when you are about out of new
    fluid in the bucket. Reconnect the hoses. Check the fluid level and
    top off as needed. Start the engine up and let it idle while you
    check for leaks. Drive it slowly to check the opperation of the
    tranny and re-check for leaks. Then take it out for a normal drive
    (including some hi-way time) to make sure all is ok, and re-check for
    leaks. That should get you as near a complete fluid change as you can
    get while not sacrificing the tranny while you are doing it. As
    always YMMV.

    Good luck,
    Jeramy and Melissa Ross, Jan 27, 2004
  9. <SNIP>

    One more thing.. If you find that you are pumping fluid out, but
    nothing is getting pumped back in, then the proceedure that I gave
    isn't going to work. I ran into situations where it would work, and
    had one where it wouldn't. I should have mentioned that in my first
    post. :) Another note, I hate ATs.. as a personal pref. So I drive
    own and drive vehicles with MTs, and haven't had the misfortune to
    have to work on a AT in a while (last AT I worked on was a '97 tercel
    in 97). As always, take advice on here (including mine) with a grain
    (or a metric ton) of salt, and do what you feel comfortable with. In
    the end, that will result in you feeling better about your vehicle
    and cause you to enjoy it more. That's all that really matters.
    (This can be applied to pretty much all threads in auto groups like
    "which brand of oil is best?" or
    "which brand of filter works better?" etc.) I am sure some really
    anal people will disagree with me, but that's life. YMMV (your
    millage may vary)

    Best wishes,
    Jeramy and Melissa Ross, Jan 27, 2004
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