Am I playing with fire?
 

Guys and girls...

Every month, for the past few months, have been replacing just over 900ml of old ATF with new ATF, without resetting the computer etc. The rationale is that slowly rejuvenating the ATF will give the computer more than enough time to adjust to the changes.

Is this sound, or am I pushing my luck?

Just get it done properly ! why are you diluting new clean oil with dirty old oil? :-)

I assume that a full drain of an auto box including the torque converter would need workshop equipment. I suppose that for DIY on the front drive it is probably easier to just dump what isn't in the torque converter and replace it and over a period of time the old oil gets less and less dirty. Possibly better than doing nothing if you cannot afford to pay a garage to do the job. Or is there a pitfall that I have missed?

Firstly, you wont cause any damage by not resetting the TCM adaptations, but you might not get the best results.

If you want to do partial changes rather than a full flush (which is a perfectly acceptable approach) assuming it's a TF80 you would normally drop as much as would come out (3~3.5 L) and then replace exactly the same amount in new fluid. Drive 50-100 miles, repeat twice, then you will have fluid that is ~90% new.

It's best practice to reset the TCM adaptations and that does give the best results but if you don't have the diagnostics to do that or the funds to get a garage to do that - I would still do the fluid changes as it will extend the life of your gearbox.

And oh boy is it dirty!

Unfortunately money is tight hence my current method. I've assumed the "adaptations" will adapt to the (slowly) changing fluid even though I haven't reset anything, but it's just an assumption, so I may be (very) wrong. I'm only dropping ~900ml at a time because I'm only removing the little torx screw.

You'd be better dropping as much as possible as per Tannaton's advice. 900 ml is never going to get you to the tipping point:teeth_smile:

I've done this sort of thing loads of times in the past - I can't see a problem - even if the level is a bit out I don't see a problem - and the transmission is adaptive - it'll adapt! I do something similar with my XC90 T8. I bought it at 60K miles it's coming up to 90K the fluid looks better now than when I bought it with 10K interval partial drain and top-ups (I do the partial drain and top-up with each (10K) oil change - even though I've never done a multi-flush. I've been using the AS.1 spec Comma fluid - not the official Volvo stuff. I'll probably be lynched by the Volvorati at some point for the sacrilege! :regular_smile: I will probably do a multi-flush at 90K miles and then drop to 20K intervals for refreshes thereafter. The fluid was pitch black when I bought the car - it has a hint of red now.

That's always the case - the transmission holds about 12 litres you can only get about 4 litres out with a sump drain.

Unless you're driving the car really hard, I suspect 900ml of fresh fluid monthly will be a net-benefit to the health of the fluid - ie it'll remove more suspended crap from the fluid than gets accumulated in a month. Go for it - it's certainly going to do no harm.