? about drain and fill for ATF...

[RobPatt 93 525ia]

in the 93 w/o dipstick, though not 'lifetime fluid' Bentley gives an elaborate procedure to get the ATF to temp, then drain, then fill, bring to temp, check level, repeat until level is correct......

If all the ATF is at the same temp, (ATF in the tranny and new ATF in the bottle) why can't I just drain x amount and refill w/new ATF of the same quantity? I could do this first thing in the a.m. when all fluid temps are equal, ideally making the drain and fill process much simplier.

Am I missing something, or is this an acceptable method?
Thanks, Rob sends....

[Dick Schneiders]

The only difference is that both of my cars are 1991's and they do have the dipstick/fill tube which makes the refill and checking of fluid a whole bunch easier.

I drain when cold, measure amount and refill with the same amount of Dexron III. I do check the dipstick level several times under different fluid temperatures over the next few days to make sure that the level is in the normal range. There is a small difference on the dipstick depending on the temperature of the fluid, but I think the primary reason is simply that when the fluid is at the prescribed temperature, then the measurement is most accurate. While you don't want to overfill, just like on engine oil, there is a range that is acceptable and the amount doesn't have to be "spot on", just close. I agree, but I am no expert, that if you put back the same amount that is taken out and it is the same temperature it should be ok. This only works, though, if the fluid level *before* draining is at the acceptable level. I would think it unlikely that the level before draining would be too much fluid, so the more likely situation is that the fluid level is either correct or a bit low. If you replace what you take out you shouldn't have a situation of too much fluid, but might have a bit less than is recommended. That is why I do the checks of my fluid level with the fluid warmed up, after I do the refill. I want to be certain that there is enough fluid in the system. It is easy because I have a dipstick.

Don't know if this helps, but I am agreeing with what you said.

in the 93 w/o dipstick, though not 'lifetime fluid' Bentley gives an elaborate procedure to get the ATF to temp, then drain, then fill, bring to temp, check level, repeat until level is correct......

If all the ATF is at the same temp, (ATF in the tranny and new ATF in the bottle) why can't I just drain x amount and refill w/new ATF of the same quantity? I could do this first thing in the a.m. when all fluid temps are equal, ideally making the drain and fill process much simplier.

Am I missing something, or is this an acceptable method?
Thanks, Rob sends....

[RobPatt]

The only difference is that both of my cars are 1991's and they do have the dipstick/fill tube which makes the refill and checking of fluid a whole bunch easier.

I drain when cold, measure amount and refill with the same amount of Dexron III. I do check the dipstick level several times under different fluid temperatures over the next few days to make sure that the level is in the normal range. There is a small difference on the dipstick depending on the temperature of the fluid, but I think the primary reason is simply that when the fluid is at the prescribed temperature, then the measurement is most accurate. While you don't want to overfill, just like on engine oil, there is a range that is acceptable and the amount doesn't have to be "spot on", just close. I agree, but I am no expert, that if you put back the same amount that is taken out and it is the same temperature it should be ok. This only works, though, if the fluid level *before* draining is at the acceptable level. I would think it unlikely that the level before draining would be too much fluid, so the more likely situation is that the fluid level is either correct or a bit low. If you replace what you take out you shouldn't have a situation of too much fluid, but might have a bit less than is recommended. That is why I do the checks of my fluid level with the fluid warmed up, after I do the refill. I want to be certain that there is enough fluid in the system. It is easy because I have a dipstick.

Don't know if this helps, but I am agreeing with what you said.