Proper use of the Tranny Oil Change Calculator

[azsynthetic]

First, I would like to say that the Transmission Oil Change Calculator (TOCC) is a very fine tool. But, there is more than just straight dump and refill estimate that you can do with the calculator. The example I am giving below is of my Chevy K1500 with a TH700R auto. The total transmission capacity is 10 qt with about 4.5 qt in the torque converter, about 0.5 qt in the line, and 5.0 qt in the pan.

If I pull the cooler line and do a complete flush then I need about 11 qt to do it right (i.e 100% clean oil). If I do a dump and refill twice of 5 qt each time then I will ended up with 75% clean oil. What if instead of a dump and a 5 qt refill twice I do a dump and refill of only 3 qt each time for three times?

Plugging this into the TOCC with 8 for the Total Volume of Transmission and 3 for the Volume changed I get 76% clean oil after 3 oil change. But, since my transmission now only has 8 qt instead of 10 qt I need to top it off with 2 qt for a total of 11 qt used. The 24% of old oil in the final 8 qt is now actually only 19% of the 10 qt full capacity. So, the final number is 81% clean oil with just 11 qt used.

The time it takes me to do an extra oil dump is less than 5 minutes but I ended up with more clean oil in the transmission. The saving is even greater if you are shooting for a higher percentage of clean oi. For example, a 99% clean oil would require 35 qt doing a 5 qt dump/refill instead of only 29 qt for a 3 qt dump/refill.

 

[Donald]

So the first time you are dumping 5 qt but only adding back 3 qt, so running the AT 2 qt low? You then assume this 2 qt low condition will mean the next dump and refill will dump only 3 qt out? (Is this true, maybe the torque converter will also be low, I do not know?). Most people would not want to run the vehicle 2 qt low to get to the next dump & refill.

I still say if you only want to freshen up the fluid still in good condition, then go with dump and refill (once or twice). If you have old dark brown/black fluid, then a drain, filter replacement and flush is what is needed.

 

[Gary Allan]

The stuff in the converter won't be a FIFO (first in:first out) ..it will be a mixture that will eventually get "clean enough". You've got a washing machine in there that's getting clean fluid introduced ..but expelling a blend.

 

[azsynthetic]

Quote:

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So the first time you are dumping 5 qt but only adding back 3 qt, so running the AT 2 qt low? You then assume this 2 qt low condition will mean the next dump and refill will dump only 3 qt out? (Is this true, maybe the torque converter will also be low, I do not know?). Most people would not want to run the vehicle 2 qt low to get to the next dump & refill.

I still say if you only want to freshen up the fluid still in good condition, then go with dump and refill (once or twice). If you have old dark brown/black fluid, then a drain, filter replacement and flush is what is needed.

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You do not drive the car between dump and refill. You only need a couple of minutes of idling to mix the new with the oil fluid. Since the vehicle is not in motion, you only need enough fluid in the pan for the pump to pickup so one quart is borderline, three quarts is more than enough. The torque converter is always full unless the engine is running when the pan is empty.

You will get more clean fluid by doing a partial fill with the same amount of ATF. The result is even better with my F350 transmission, 20 quarts capacity with 10 quarts in the pan.