Next door neighbour has a '99 BMW 540i, which I reckon has about 284,000 km (177,500 miles) on the clock. It's a German gray import and he's never changed his ATF, based on the manual's referral to 'lifetime fill'. There isn't an English publication, and he speaks/reads German, so that was handy. The torque converter went out last month, and when he had it replaced, the mechanic put back his old ATF as opposed to fresh ATF.
Having a word with him today, he was asking if he could slowly replace his ATF...as in a litre every oil change. I wasn't too sure, but we decided we would replace a litre.
Went out to get some ATF, and I was told this transmission requires a 'special fluid', which nobody had. Finally, we found what they were referring to Liqui Moly ATF III. At $9.45 a litre, it was ridiculously priced but I was told it's "synthetic"...only to find out it's mineral when I check it online. Stupid thing is, there's nothing special about it at all...it's just Dexron III/Mercon. Anyhow, we replaced a litre and the transmission shifts as smooth as a baby's bottom.
Now the silly thing is, there is nothing mentioned in the manual about ATF, other than "lifetime fill". I reckon this vehicle requires an ATF meeting ZF spec? 
Secondly, considering the transmission's running much smoother after replacing just a litre, would it be a good idea to stick to his plan and replace a litre at every oil change...or perhaps perform a cooler line flush and change it all? The old ATF looked really dark red, somewhat brown...but colour doesn't really mean much. Thanks!
Secondly, considering the transmission's running much smoother after replacing just a litre, would it be a good idea to stick to his plan and replace a litre at every oil change...or perhaps perform a cooler line flush and change it all? The old ATF looked really dark red, somewhat brown...but colour doesn't really mean much. Thanks!
