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I have an automatic transmission whose total capacity is X quarts of ATF.
With every drain/refill operation, I drain Y quarts out and refill with Y quarts of new ATF.
Then I drive a few miles to mix the old and new transmission fluids.
I then repeat the process, draining Y quarts out and refilling with Y quarts new.
The question:
How many quarts of the original ATF remain in the transmission after n drains and refills?
To use real numbers, I have a Honda whose automatic transmission holds 6.9 quarts of ATF.
With each drain I get 3 quarts from the transmission, and I add 3 fresh quarts of ATF.
Thus after one ATF drain and refill, the transmission ATF is a mixture of 3 quarts new and 3.9 quarts old.
If I do this 3 times, how many quarts of the old ATF remain in the transmission?
How many drains/refills would it take to get less than 1 quart of old ATF remaining?
To win the apple you must come up with an equation of the form:
I would suggest you post this in the education forum, but gear heads may be the best suited to give you an answer. In high schools autotech counts as a math credit.
How many quarts of the original ATF remain in the transmission after n drains and refills?
To use real numbers, I have a Honda whose automatic transmission holds 6.9 quarts of ATF.
With each drain I get 3 quarts from the transmission, and I add 3 fresh quarts of ATF.
Thus after one ATF drain and refill, the transmission ATF is a mixture of 3 quarts new and 3.9 quarts old.
If I do this 3 times, how many quarts of the old ATF remain in the transmission?
How many drains/refills would it take to get less than 1 quart of old ATF remaining?
You will always have 6.9 qts of old ATF since the fresh 3 qts is immediately contaminated by the remaining old ATF.
A machine flush is the closest you'll come to completely new fluid.
I have an automatic transmission whose total capacity is X quarts of ATF.
With every drain/refill operation, I drain Y quarts out and refill with Y quarts of new ATF.
Then I drive a few miles to mix the old and new transmission fluids.
I then repeat the process, draining Y quarts out and refilling with Y quarts new.
The question:
How many quarts of the original ATF remain in the transmission after n drains and refills?
To use real numbers, I have a Honda whose automatic transmission holds 6.9 quarts of ATF.
With each drain I get 3 quarts from the transmission, and I add 3 fresh quarts of ATF.
Thus after one ATF drain and refill, the transmission ATF is a mixture of 3 quarts new and 3.9 quarts old.
If I do this 3 times, how many quarts of the old ATF remain in the transmission?
How many drains/refills would it take to get less than 1 quart of old ATF remaining?
To win the apple you must come up with an equation of the form:
Quarts of old ATF remaining = f(X, Y, n)
I don't know how to put it into an equation form, but after three changes you'd have .9 quarts of old, and 6 of new fluid in there.
EDIT: Hmm. That's not correct either. It's close, but I was assuming a 50/50 drain of old and new since the capacity is 6.9 and each change removes almost half of it.
I don't know how to put it into an equation form, but after three changes you'd have .9 quarts of old, and 6 of new fluid in there.
EDIT: Hmm. That's not correct either. It's close, but I was assuming a 50/50 drain of old and new since the capacity is 6.9 and each change removes almost half of it.
You're close; you get the apple. After three changes there would be 1.25 quarts of the old transmission fluid remaining in the mixture.
The equation is:
# quarts of old ATF remaining in an X-quart capacity transmission when swapping Y-quarts n times
= X*(1-Y/X)^n
The reason this came up was that it's been some time since my last ATF replacement (like never!) and, being lazy, I took my car to the Honda dealer to see what he would charge. It was $91 for a single drain/refill. I was shocked, Shocked I'd say! Doing an ATF drain/refill is easier than doing an oil change. He also wanted about $10 a quart for Honda ATF DW-1. Wow, just wow!
Needless to say, I'll be doing the job myself. Honda DW-1 can be bought online for about $6/qt plus shipping.
See, for example, http://www.handa-accessories.com/
The job should be done after recently driving the car, when the ATF is hot. I'd recommend workman's gloves. Also, leave the fill port closed when starting to drain; this keeps the fluid from gushing out at the start of the operation. Otherwise, it's ducks soup.
Yes you can work out dilution ratios or you can do it the easy way. Use the cooler lines. Take the output line and redirect it into a container, start car, allow 3 quarts to pump out, shut off, refill with fresh, repeat cycle. There will be intermixing, but I would estimate that if you performed this cycle 3 times with 9 quarts of fresh fluid you should end up with about 95% new fluid. The fluid circuit is fairly linear inside the transmission. Go down to the parts store and pick up a bottle of Lubeguard Red or Lucas Conditioner (not the leak fix garbage). The Lubeguard is more highly recommended.
If you want to do it the long, messy, labor intensive way of dropping the pan each time then your ratios will work like this:
1st 3 quarts -> 43% new fluid.
2nd 3 quarts -> 68% new fluid.
3rd 3 quarts -> 82% new fluid.
4th 3 quarts -> 90% new fluid.
You will always have 6.9 qts of old ATF since the fresh 3 qts is immediately contaminated by the remaining old ATF.
A machine flush is the closest you'll come to completely new fluid.
I initially agreed with this until I reread the OP. They are asking how much of the original fluid is remaining. That eliminates all fluids put in after the first change.
I don't know if you can come up with an equation that effectively works for this, unless you can accurately anticipate the amount of mixture between the old fluid and the new fluid. Honestly, you'll have no new fluid after you've driven around a bit and mixed the old and new fluid together. By the way, does the filter change as well?
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