DIY Transmission Fluid Change?

[miccris93]

I want to do a transmission fluid change on my 2000 I30 relatively soon, as it hasn't been changed and the car sits with ~35k miles. My friend checked it for me (took auto classes for 4 years) and the fluid looked like it wasn't so red any more, so I think a change is in order, especially with hard shifts after the car sits cold overnight, but is seamless after a few minutes of driving. I had posted in the Maxima/I30 forums and Towncivilian gave me these steps:
"You will need:
12 to 15 quarts of automatic transmission fluid, preferably Nissan Matic D
A clear gallon jug, something like an empty milk jug
Another large container to store used fluid for disposal

1. Disconnect the transmission cooler return line and secure it in a collection bucket such as a clear gallon milk jug. This will be the hose on the driver side of the vehicle; disconnect the end leading towards the transmission.
2. Have a helper start the car while you watch the bucket - once it's half full (2 quarts), yell for the helper to stop the engine.
3. Add 2 quarts of ATF through the transmission dipstick.
4. Drain collection jug into larger jug (i.e. a Disposoil - these only hold 10 quarts though in my experience, so have something else to hold the last 5 quarts).
5. Repeat steps 2-4 until you're out of ATF.
6. Check fluid for proper level (see the next question and answer for details), and recycle the old ATF. Any place that takes used oil will likely recycle ATF."

I was telling my dad this (I'm 18, so I always ask him anything before I do anything major) and he said that wasn't the best thing since as you refill the transmission eery 2 quarts, you would be mixing new fluid with old fluid. He suggested taking not only the return line off, but also the feed line. That way, as the old fluid goes out, the new goes in. Would this be a better way, or should I stick to the empty-fill every 2 quart way? (I'd think that by the time it gets circulated, the new fluid wouldn't really get mixed with the old) Thanks for any advice!

[Towncivilian]

I'm not sure whether using both lines will provide the necessary suction to suck the fluid out of the container, I've never tried doing so. If you're quick enough, you can perform the method suggested in the newer Nissan FSMs. Basically, instead of draining 2 quarts at a time, shutting the engine off and refilling and repeating, you disconnect the cooler return line into a suitably large jug to hold the entire transmission capacity + 30 - 50% and as the fluid drains with the engine idling, continually add fluid through the transmission fluid dipstick.

Either method should exchange all of the fluid without leaving a significant amount of old ATF behind - this is why 30 to 50% more fluid than the transmission's total capacity is recommended. I've used the method I described and after 12 quarts the fluid exiting the cooler line was bright cherry red, indicating new fluid.

[miccris93]

Thanks for the additional input town'! I was also wondering, would just draining the trans dry even just in Park cause damage (and then to just add the fluid back back once no more comes out)? Although probably whatever anyone says, I wouldn't want to risk anything. Or I guess it would be like you said and to just keep adding fluid as it drains. Probably doing the two quarts at a time is safest so that the transmission always has lubrication.

[Towncivilian]

Even if you drain the trans "dry", there's still a film of oil present to prevent any significant damage for a short period of time, that and the transmission isn't under any load at all - and even then, when you see the cooler line flow starting to spurt and die and/or you see bubbles in the fluid exiting the trans, you're supposed to yell for your helper to turn off the engine. If I recall correctly, some manufacturers actually recommend to just disconnect the line and drain until the fluid flow starts slowing and then refill.

[Q451990]

I tried your dad's idea on my Q45 years ago. Although I don't know for sure that the I30 transmission is set up the same way - on the Q, the line returning to the transmission from the radiator does not have suction. The pump only pushes the fluid out to the radiator, but it doesn't suck it in from the radiator... it just relies on the pressure from the other side to push it back into the pan.

Heath