Personally I would give it at least 100 miles or more and a few weeks normal use between multiple changes.Stickyfinger wrote:reports have it a certain make of truck uses it, and up the road is a truck mechanic who "happens to have" 12ltrs in his workshop.
How much driving does it need between drains ?
Not only do you have to allow a short time for the old fluid (still in the torque converter) and new fluid to mix so that the new stuff has fully diluted and mixed with the old stuff before you drain any back out again, you also want to give time for the fresh detergent agents in the new fluid to work their magic on any deposited gunk, so that it is released into suspension in the fluid and then drained out during the next change. (Or at least half of it will be...)
If you just drove around the block between each change and did them all in one day the detergents wouldn't have time to work which means that after you'd finished all three changes the detergent would start dislodging buildups which would then float around in suspension for eternity...or at least until they get deposited again. The oil would be clean, at least initially, but the box would not be, and the oil would probably get dirty again quickly from all the deposits loosened up by the detergents being held in suspension.