Well in my endless probing around the internet I came across the Royal Purple oil brand. Its not a brand that I had heard much about, and definitely have no experience with. I was specifically interested in their claims relating to their Automatic Transmission Fluid and it's ability to keep the transmission 20F cooler than other oils, so I contacted them and asked them to confirm that the MAX ATF was the correct product for use in the 740iL (E38) gearbox. They responded that it was and put me in touch with the Australian distributor and their website, they had an article by one of the Australian car magazines which didn't test the ATF, but it did do an engine oil test (of sorts) which rated the Royal Purple product fairly highly. So if you are interested in reading that article visit http://www.royalpurple.com.au/articl...supplement.php
, it makes some interesting observations about some well known synthetic oils, and how poorly they performed in this particular test. I am interested in other members experience with this brand.
Now back to the ATF discussion, when I had the transmission oil changed (137000km) for the first time I suspect, it was nasty, black and smelly. The problem is that you only get roughly half of the oil out by dropping the pan, there is a lot left within the torque converter which is diluted by the fresh oil and progressively removed in subsequent changes. The Australian Royal Purple distibutor offered up this suggestion on getting more oil out of the system with each change: Before removing the auto pan, disconnect the return line to the transmission cooler and run the engine which will pump all the fluid out, then remove pan change filter and total refill from there.
This procedure will not harm anything and is the best way to get all the fluid out in one hit and as Chris advised using a flush in an auto is flirting with danger.
A couple of questions come to mind straight away,
1. What sort of pressure is the oil coming out of the oil cooler at?
2. The torque converter will eventually run out of oil, but is this a problem for a short time, given that as soon as the oil output falls, you turn off the engine?
3. How do you refill the torque converter once you have dropped the pan, changed the filter, seal & gasket? Is it simply a matter of filling the pan as per normal, then starting the engine for a minute to fill the torque converter body and ATF radiator, top up the pan and thenrestart the car a couple of times, checking the oil level to make sure that everything is as it should be?
Any thoughts on this suggestion by the RP Australian guy, who commented that they had a fleet of BMW hire cars that were using the RP engine and ATF oils without issue.