Calculating % of new fluid in system ?

[KGMtech]

Hi, 30 years ago I would know where to look, but that ship sailed... but the experts here should know !

Last month I did a partial change on the CVT fluid in my Maxima, I purchased 6 quarts (5.68L) of Pennzoil CVT 2 and managed to drain only 4.3 Litres from the CVT. The advertised capacity of this Jatco CVT is 10.2 Litres.

So I ended up with a mixture of 5.9 L of the old NS2 and 4.3 L of the new Pennzoil. 42% is new and 58% old fluid.

If I dump the fluid again in 1 year, and get 4.3L out, what calculation is used to determine the % of the original fluid is left in CVT?

And no, I have no issues with my CVT, it works perfectly with only 78,700km on it, so the partial change is just good preventative maintenance.

Thanks for your assistance,
Ken

 

[Sluggo0018]

If you remove another 4.3 liters at the next drain and fill, 58% (4.3 liters X .58 = 2.494 liters) of that fluid will be old fluid and 42% (4.3 liters X .42 = 1.806 liters) will be new fluid. The total amount of old fluid removed will be the original 4.3 liters, plus 2.494 liters, for a total of 6.794 liters of new fluid. This means that 66% of the fluid in the transmission will be "new".

Hope this helps.

 

[JLTD]

With the same amount going in you'd have 42% new again, which would leave 58% old. Of that 58%, 29% would be what you just added, the other 29% wouod be the original fluid.

 

[VeryNoisyPoet]

Here is an old thread I found with a download of a spreadsheet that does the calculations for you: https://bobistheoilguy.com/forums/ubbthreads.php/topics/3332159/Transmission_Partial_Drain_CAL

Just put in your system capacity and how much drains out each time and see what you get. Should have been a sticky but I guess the mods missed it.

 

[Number_35]

As you've said, you've presently got 58% old fluid left.

Each drain and fill cycle will leave you with 58% of the previous amount of fluid - it becomes a declining-balance calculation:

% of original fluid after 1st drain & fill = 58% (0.58^1)

% of original fluid after 2nd drain & fill = 34% (0.58^2 = 0.58 x 0.58 = 0.34)

% of original fluid after 3rd drain & fill = 20% (0.58^3 = 0.58 x 0.58 x 0.58 = 0.20)

% of original fluid after 4th drain & fill = 11% (0.58^4 = 0.58 x 0.58 x 0.58 x 0.58 = 0.11)

% of original fluid after 5th drain & fill = 7% (0.58^5 = 0.58 x 0.58 x 0.58 x 0.58 x 0.58 = 0.07)

And so on ... The numbers are rounded, but you get the idea. Less bang for your buck with each subsequent drain & fill.

 

[raytseng]

whenever people bring this up it seems like a banal answer to calculate old vs new.

the real value you want to know is the performance of ypur fluid as a dimension, and not a binary value.
it makes no sense to me to consider the old oil as 0% useful. similarly your new fluid is bot 100% until some magical point in time.

In 1 year it is degraded so you can't consider it as 100%.

if thr binary thinking were the case, what does it mean about your fluid the 100miles prior to your change. youre driving on bad fluid ack!!

you are better off thinking your fluid is perhaps at 90% of new performance replacing a portion of the 90% fluid improves you to 95% for example, and perhaps the fluid degrades by 1 or 2% per year. this more accurate perspective will keep you in better maintenance rather than yoyoing between extremes and striving for a meaningless 100%

 

[pbm]

Originally Posted By: raytseng
whenever people bring this up it seems like a banal answer to calculate old vs new.

the real value you want to know is the performance of ypur fluid as a dimension, and not a binary value.
it makes no sense to me to consider the old oil as 0% useful. similarly your new fluid is bot 100% until some magical point in time.

In 1 year it is degraded so you can't consider it as 100%.

if thr binary thinking were the case, what does it mean about your fluid the 100miles prior to your change. youre driving on bad fluid ack!!

you are better off thinking your fluid is perhaps at 90% of new performance replacing a portion of the 90% fluid improves you to 95% for example, and perhaps the fluid degrades by 1 or 2% per year. this more accurate perspective will keep you in better maintenance rather than yoyoing between extremes and striving for a meaningless 100%



I agree.
D & R your fluid every year or two should insure that your CVT will last a long time....

 

[Hall]

I have a copy of one of these spreadsheets. They're nice from a theoretical standpoint and they make you feel good but if you think about it, it's just doing math and it's not 100% applicable. That said, once it tells me that I've reached 75% "new", I'll feel "better" !

Funny part from a mathematical standpoint is, you'll never reach 100%. Sure, you'll get 99.99999-and so on, but it will never get there.

 

[mx5miata]

okay - you'll have a 50/50 mix of whatever doesn't drain out

 

[Rand]

how crusty is the old fluid?

I do yearly on the 2010 hyundai but it never really gets that bad so I'm ok with changing out 40% per year.

You might consider doing 2 or even 3 to start it then once a year.

The hyundai even with only 10-12k miles a year goes from fresh deep red to faded pink/brown.. and I've been doing the transmission drain and fills for 7 years now.

of course that is overkill but fluid is pretty cheap.

 

[Number_35]

Originally Posted By: raytseng
whenever people bring this up it seems like a banal answer to calculate old vs new.

the real value you want to know is the performance of ypur fluid as a dimension, and not a binary value.
it makes no sense to me to consider the old oil as 0% useful. similarly your new fluid is bot 100% until some magical point in time.

In 1 year it is degraded so you can't consider it as 100%.

if thr binary thinking were the case, what does it mean about your fluid the 100miles prior to your change. youre driving on bad fluid ack!!

you are better off thinking your fluid is perhaps at 90% of new performance replacing a portion of the 90% fluid improves you to 95% for example, and perhaps the fluid degrades by 1 or 2% per year. this more accurate perspective will keep you in better maintenance rather than yoyoing between extremes and striving for a meaningless 100%
Agreed, but some of us have done a drain and fill followed by a short drive followed by another drain and fill the same day. For all practical purposes the fluid added first will not have measurably degraded vs. the fluid added later in the day.