Synthetic in the Differential?

[Tone]

A flush is the ONLY way to get all the fluid changed out in a tranny - all 9.1 qts. A drain and refill only gets about 3-4 qts out and leaves the majority of the old fluid in. Dropping the pan and changing the filter gets the same amount but should be done every other change IMHO and is good to do after flushing with synthetic since that fluid has a longer life. Although it is a chore, the filter will not clean itself and a clogged filter will eventually kill the tranny.

[VX4EJR]

A flush is the ONLY way to get all the fluid changed out in a tranny - all 9.1 qts. A drain and refill only gets about 3-4 qts out and leaves the majority of the old fluid in. Dropping the pan and changing the filter gets the same amount but should be done every other change IMHO and is good to do after flushing with synthetic since that fluid has a longer life. Although it is a chore, the filter will not clean itself and a clogged filter will eventually kill the tranny.

So I went to an Isuzu dealer/service shop and they drained the trans and hooked up to the trans cooling line to flush it, and then filled the trans fluid back in to the tune of 12 quarts (I supplied the 12 quarts with Mobil 1 ATF).
I showed the shop guy my owners manual that said the capacity is 9.1 quarts for the tranny, he just said....well that doesn't include fluid in the lines, etc.
Does this sound right?? Can you really put 12 quarts into our trannys???
Seems to drive OK, maybe a little bit clunkier now when the auto trans down shifts, weird. Any thoughts from the group?

[Joe_Black]

Tranny capacity is 9.1 quarts for our flavor of the 4L30E, which does not include the torque converter, lines or cooler. So 12 should be about right.