Transmission fluid change question .DIY

[Reeeeeeee]

2015 bmw sDrive

Is it possible to get a suction tube from the fill plug to drain a few QTs out of the transmission without dropping the pan. I want a fluid refresh not a whole trans job i have 4 Qts left over fluid so why not....

33k miles on car no need to change the filter fluid is old doe.

[Reeeeeeee]

one more question does the trans pan have a drain hole ? if i recall it doesn't but aftermarket versions do ?

[maxwmiller]

Originally Posted by Reeeeeeee

2015 bmw sDrive

Is it possible to get a suction tube from the fill plug to drain a few QTs out of the transmission without dropping the pan. I want a fluid refresh not a whole trans job i have 4 Qts left over fluid so why not....

33k miles on car no need to change the filter fluid is old doe.

Is it possible: yes. The trans pan should have a drain plug that you COULD remove some fluid from and pump in new fluid through the fill plug.

Should you do it: IMO, no. Unless you drop the pan, there's gonna be quite a bit of fluid left up there. Keeping old, dirty fluid in your trans isn't worth the very small amount of money you'll save by not doing the job properly. Also, that filter needs to be replaced eventually.

Also, four quarts probably won't be enough to replace what drains out. Your transmission (I'm assuming you have the ZF8) has a capacity of around 8 liters.

[Gamb1t]

It's not a challenging job to do the drain, pan replacement and refill. Just have to keep in mind of the refill process that requires specific temp range.

Do the whole thing and be happy with the knowledge that you completed the work in a fulsome way.

[bosstones]

Sorry if this is thread jacking but it's somewhat related. I heard somewhere that, short of a full flush, a drain/fill (incl pan drop) only changes out 60-70% of the trans fluid . Thus a 2nd drain/fill is needed to get closer to a full swap (al beit still not at 100% but close enough).

Is that real or fake news? I never figured it was 100% for a single change but figured it was in the 80% (-ish) range. 60% would be pretty dismal but still worthwhile if it's never been touched at all.

Asking since Ive been meaning to do my trans fluid since I'm at 85k on the clock but was also going to do the sleeves, solenoids, etc... Ive got spare drain and fill plugs and fluid for a 2nd fluid change if needed but it wouldn't be worth doing the pan et all first should I do 2 fluid changes.

[Gamb1t]

I think there will always be some left inside the tranny itself and along the cooling lines. I wouldn't worry about it.
Just like engine coolant and oil, you don't really swap out fully. Besides how can you tell the ratio of new or old oil with 2nd round draining?

[maxwmiller]

Originally Posted by bosstones

Sorry if this is thread jacking but it's somewhat related. I heard somewhere that, short of a full flush, a drain/fill (incl pan drop) only changes out 60-70% of the trans fluid . Thus a 2nd drain/fill is needed to get closer to a full swap (al beit still not at 100% but close enough).

Is that real or fake news? I never figured it was 100% for a single change but figured it was in the 80% (-ish) range. 60% would be pretty dismal but still worthwhile if it's never been touched at all.

Asking since Ive been meaning to do my trans fluid since I'm at 85k on the clock but was also going to do the sleeves, solenoids, etc... Ive got spare drain and fill plugs and fluid for a 2nd fluid change if needed but it wouldn't be worth doing the pan et all first should I do 2 fluid changes.

The capacity for the BMW ZF8's is officially 8 liters. Unless you take the whole transmission out, you won't get more than ~5 liters to drain. Just refill what you got out and you should be fine. If you care about the math, 5/8 = ~63%. Do it twice, you get 86% out. Either way, don't forget to replace the pan or else you'll still have your old filter.

I changed my fluid twice, two weeks apart. Fluid was pretty dirty on first drain (93k!). On the second drain, it was noticeably less dirty, but still not fresh. The job is only takes an hour and isn't that expensive, so IMO probably worth to just do it twice, especially if you're getting up there in miles and it hasn't been done before.