8HP70 8 Speed Automatic Transmission

[HarryH]

8HP70 8 Speed Automatic Transmission capacity is 8.8 quarts. While perforating the service, only 5 quarts were drained! I'm assuming the other 3.8 quarts a in the torque converter and some residual in the transmission cooler.
Another assumption is the Mopar 68218925AB is in fact repackaged ZF Life Guard 8. The bottle says "Shake Well" before using! Anyone know why?

 

[tidefan1967]

Yes the additional fluid is in the torque converter mostly. As far as shaking the fluid goes some of the additives can fall out of suspension if it has been sitting around for a long time so shaking the bottle kind of mixes it back up again.

 

[c3k]

8HP70 8 Speed Automatic Transmission capacity is 8.8 quarts. While perforating the service, only 5 quarts were drained! I'm assuming the other 3.8 quarts a in the torque converter and some residual in the transmission cooler.
Another assumption is the Mopar 68218925AB is in fact repackaged ZF Life Guard 8. The bottle says "Shake Well" before using! Anyone know why?

FWIW, my Honda Pilot ( '03, 300k miles and going strong) has a similar transmission fluid retention. It specifies NOT to flush it: only drain and fill. Repeat 4 more times.

Given your numbers, 5 quarts drain out of 8.8 quart capacity, that means 3.8 quarts of "bad" fluid remains. So, 3.8/8.8 means you've got .43 (43%) "bad" fluid. If you drain, refill, drive (to mix it up), and then repeat for a TOTAL of 4 drain/refill cycles, you'd get 96.5% "new" fluid. (0.43^4 = .035 "bad". Therefore, 1 - 0.035 = .965 "good").

Were you to do this one more time, you'd only get to 98.5%, a 2% improvement. (One less time would be 92%.)

Choose what level of fresh fluid you want.

 

[SpeedyV]

FWIW, my Honda Pilot ( '03, 300k miles and going strong) has a similar transmission fluid retention. It specifies NOT to flush it: only drain and fill. Repeat 4 more times.

Given your numbers, 5 quarts drain out of 8.8 quart capacity, that means 3.8 quarts of "bad" fluid remains. So, 3.8/8.8 means you've got .43 (43%) "bad" fluid. If you drain, refill, drive (to mix it up), and then repeat for a TOTAL of 4 drain/refill cycles, you'd get 96.5% "new" fluid. (0.43^4 = .035 "bad". Therefore, 1 - 0.035 = .965 "good").

Were you to do this one more time, you'd only get to 98.5%, a 2% improvement. (One less time would be 92%.)

Choose what level of fresh fluid you want.

When I had GM HD trucks, both with transmission coolers, we used the so-called “Hoot method” to get around this (if the filter didn’t need replacement). We would simply remove the return line from the cooler and drain a measured amount while adding the same amount through the fill hole, running the truck as needed to allow the transmission to pump itself clear. When the fluid coming out matched the fluid going in, you knew you were done. I wish everything were that easy!

 

[c3k]

When I had GM HD trucks, both with transmission coolers, we used the so-called “Hoot method” to get around this (if the filter didn’t need replacement). We would simply remove the return line from the cooler and drain a measured amount while adding the same amount through the fill hole, running the truck as needed to allow the transmission to pump itself clear. When the fluid coming out matched the fluid going in, you knew you were done. I wish everything were that easy!

That's a great method. It uses the normal transmission pump pressure and rate of flow.

(For ZF transmissions, part of the fluid change includes dropping the pan and replacing it. The pan as an integral filter and magnets. I'd only drop the pan the once...)