David Spektor said:
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?
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