In researching about how to service my own transmission on my 2002 Toyota Sienna I naturally came across the drain and refill method. And what I noticed from some of the post was that people would drain their transmission then fill it then drive it for x amount of time and drain and refill again and they may do this two or three or four times. Obviously the idea being to get as much fresh tranny fluid in there as possible.
But what I haven't heard anybody point out, maybe because it's so obvious that it's not necessary, then again maybe it's not so obvious, is the waste of good transmission fluid using this method. Let me just give an example to show what I mean.
For the sake of argument let's say your transmission holds 4 quarts. So you drain out 1 quart and then you put in 1 quarter of fresh. Your transmission fluid now has 25% fresh fluid in it. Now you drive your car around for a couple of days to mix up the old with the new fluid and then you drain off another quart. Unfortunately you're not just draining off old transmission fluid now. 25% of that fluid you are draining off is the new fluid you put in there. So when you add your new quart back in you're not adding a full quart of new fluid to the old, for now a total of 2 new quarts in your system, you are replacing that 25% of of a quart of the new fluid you just drained. And now only 75% of that from quart is new fluid in your system.
Therefore your transmission does not have 2 new quarts in it for 50% new in this 4 quart system after this second drain and fill, it has 1.75 new quarts. And I think that give you 37% new.
Then you repeat the procedure for a third time and now you're draining off yet more new (37%) transmission fluid from the last two days procedures and the one quart you now put in has to replace that 37% and then the 63% that is old.
And it goes on and on like that to where each time the precent of the new transmission oil you are draining out, and throwing away, is a greater and greater percentage.
My own car holds about 8 quarts total. The math I did for it told me that if I wanted to achieve a 75% freshness rate of my transmission fluid using the multiple drain and refill method, assuming I did 2 quarts at a time, I would have to do that 10 times. In other words I would have to use about 20 quarts to get 6 quarts worth freshness in the system.
And I use 2 quarts for my example because the suction pump I got is only able to get out 2 quarts at a time. But the math carries out, Each time you drain and refill you're taking out X% of the fresh fluid you put in from the prior procedure(s).
And drain and refill once every 30000 miles?
That means that at 30,000 miles X percent of your fluid will be fresh and x percent have 30,000 miles on it.
Then you do that again at 60,000 miles you have X percent that is fresh, X percent with 30,000 miles on it and X percent with 60,000 miles on it and so on and so forth. That all doesn't sound good to me.
Of course a lot of this falls under the better than nothing category, especially if you do not have the luxury of owning the car from new and starting a proper service schedule and method. And then it seems that draining as much as you can in one sitting is the better way to go. Like from the cooling lines.
Ok. Just putting this out there as a bit of consciousness raising. If my theory is wrong please tell me. I would very much like it to be.
But what I haven't heard anybody point out, maybe because it's so obvious that it's not necessary, then again maybe it's not so obvious, is the waste of good transmission fluid using this method. Let me just give an example to show what I mean.
For the sake of argument let's say your transmission holds 4 quarts. So you drain out 1 quart and then you put in 1 quarter of fresh. Your transmission fluid now has 25% fresh fluid in it. Now you drive your car around for a couple of days to mix up the old with the new fluid and then you drain off another quart. Unfortunately you're not just draining off old transmission fluid now. 25% of that fluid you are draining off is the new fluid you put in there. So when you add your new quart back in you're not adding a full quart of new fluid to the old, for now a total of 2 new quarts in your system, you are replacing that 25% of of a quart of the new fluid you just drained. And now only 75% of that from quart is new fluid in your system.
Therefore your transmission does not have 2 new quarts in it for 50% new in this 4 quart system after this second drain and fill, it has 1.75 new quarts. And I think that give you 37% new.
Then you repeat the procedure for a third time and now you're draining off yet more new (37%) transmission fluid from the last two days procedures and the one quart you now put in has to replace that 37% and then the 63% that is old.
And it goes on and on like that to where each time the precent of the new transmission oil you are draining out, and throwing away, is a greater and greater percentage.
My own car holds about 8 quarts total. The math I did for it told me that if I wanted to achieve a 75% freshness rate of my transmission fluid using the multiple drain and refill method, assuming I did 2 quarts at a time, I would have to do that 10 times. In other words I would have to use about 20 quarts to get 6 quarts worth freshness in the system.
And I use 2 quarts for my example because the suction pump I got is only able to get out 2 quarts at a time. But the math carries out, Each time you drain and refill you're taking out X% of the fresh fluid you put in from the prior procedure(s).
And drain and refill once every 30000 miles?
That means that at 30,000 miles X percent of your fluid will be fresh and x percent have 30,000 miles on it.
Then you do that again at 60,000 miles you have X percent that is fresh, X percent with 30,000 miles on it and X percent with 60,000 miles on it and so on and so forth. That all doesn't sound good to me.
Of course a lot of this falls under the better than nothing category, especially if you do not have the luxury of owning the car from new and starting a proper service schedule and method. And then it seems that draining as much as you can in one sitting is the better way to go. Like from the cooling lines.
Ok. Just putting this out there as a bit of consciousness raising. If my theory is wrong please tell me. I would very much like it to be.
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