Doing drain and fills that will ultimately lead to a pan drop and filter replacement on a high mileage auto, which is a more involved job. But just attempting to get the fluid freshened up in the short term, since it's very simple and relatively mess-free with a Mityvac (excellent tool). I understand that there is a partial fill formula, and each successive drain removes some % of new fluid. This is going to vary based on car and how effective a drain is, whether you have a drain plug or using a Mityvac, and how much you can extract.
This question is not car specific, more generic. When doing short interval ATF drain and fill on a high miles automobile that has visually worn looking fluid, do you shoot for a specific shade of color or an approximate % of new fluid replaced - for instance, approximately 50% or 75% or 90%, etc.?
I have one rig that I've completed 3 iterations and am currently at about 66%, and another 4 qts D&F will get me to about 76%. Fluid is currently a dark cranberry but should be a light cranberry color when new. Thereafter, around 80% on another successive. So even though I'm pulling out good fluid, I'm also eliminating dirty fluid. The question is, when do you think it's good enough?
In this case, the capacity is about 14 qts and I'm replacing about 4 qts each time, and I've worked out the math to be approximately:
1. 30% new fluid
2. 51%
3. 66%
4. 76% new, and draining out about 3/4 of the "new" fluid at this point.
5. 83%
And quickly diminished returns thereafter, draining out almost all new fluid at this point.
The fluid is not expensive, probably $20 for each iteration. Transmissions are expensive, so obviously I'd want newer fluid at a reasonable investment. I'm contemplating doing 1-2 more rounds, and then draining and doing a pan drop and filter swap when I have a full free afternoon to mess with it.
This question is not car specific, more generic. When doing short interval ATF drain and fill on a high miles automobile that has visually worn looking fluid, do you shoot for a specific shade of color or an approximate % of new fluid replaced - for instance, approximately 50% or 75% or 90%, etc.?
I have one rig that I've completed 3 iterations and am currently at about 66%, and another 4 qts D&F will get me to about 76%. Fluid is currently a dark cranberry but should be a light cranberry color when new. Thereafter, around 80% on another successive. So even though I'm pulling out good fluid, I'm also eliminating dirty fluid. The question is, when do you think it's good enough?
In this case, the capacity is about 14 qts and I'm replacing about 4 qts each time, and I've worked out the math to be approximately:
1. 30% new fluid
2. 51%
3. 66%
4. 76% new, and draining out about 3/4 of the "new" fluid at this point.
5. 83%
And quickly diminished returns thereafter, draining out almost all new fluid at this point.
The fluid is not expensive, probably $20 for each iteration. Transmissions are expensive, so obviously I'd want newer fluid at a reasonable investment. I'm contemplating doing 1-2 more rounds, and then draining and doing a pan drop and filter swap when I have a full free afternoon to mess with it.