Got me a 540i wagon—to TCT or not to TCT?

[chowza]

Minor note - general forum practice is to reply below the quote as it reads a bit easier for people to see who/what you're responding to (opposite to an email reply w. the prior convo listed below)

Flush will be a pain at this time in our neck of the woods. To really change properly you need to drain as much as possible, fill w/ water, run that for a few minutes or so, then drain again. Best done outside in warm weather needless to say. Otherwise you end up with pockets of the old stuff. To do a reasonably full drain, you need these points...
1. Remove the tranny cooler line from the drivers side bottom corner of the radiator. That's where manuals have a nice drain plug. Auto's connect the tranny cooler there instead. Its a twist-and-pull type of a scenario for that fitting (imagine you're removing a twist-plug instead, uses exact same radiator/fitting).
2. On the lower sides of the block, there are big plugs on either side that are what allow you to drain most of the rest. They are fairly easy to spot but less easy to get the wrench on. In theory you have fresh new crush washers ready to put on the plugs when they go back on. Guys here will take both sides of whether thats required or not. Crush washers are cheap if you have time to pick them up tho.

There will be a few little pockets that can't completely drain (bottom of valley pan, heater core) but that's what the refill-with-water-and-repeat trick is for, to dilute those pockets as much as possible before you put the good new clean stuff in.

Alternatively you can A. just try draining at the radiator, but then run multiple water refills (giant pain, will take much longer for water to be clear), or, B. use the old Prestone 'flush kit' to cut a hose and continuously run water through the motor until its clear... personally I woudln't do that unless I had an old used discard coolant hose to cut up... I'd basically stick with the factory method honestly, the PITA of those block plugs is probably less than either of the other 2 things.

Anecdotally, mixing the green and VW/Audi coolants (i.e. the G11-G12 pinks & purples since the mid-90's) makes an ugly awful brown sludge that stains the expansion tanks and sometimes creates sticky gooey residue, and I've been through that multiple times, buying new exp tanks multiple times. I've spend hours doing a 'proper flush' and $$$ on proper OEM coolant only to pickup the car from a mech a month or two later and find he's thrown it all away and put in cheap green crap. Oh I've had that happen more than once. F___ing a-hoelz.

You shouldn't have that problem with green and blue I don't think, my understanding is the BMW/Pento blue stuff is much more forgiving than the VW/Audi G11 was... however if the mystery green they put in there does NOT play nice with the factory blue, that could explain some of the little bits of sludgey residue you're seeing.

Thanks for the advice, etiquette-wise and coolant-wise! Email habits die hard.

I decided to just do a fill/bleed for now. Topped it off and bled it, then took it for a short drive this morning. Going to wait for the engine to cool then check the level again. FWIW, re the "is my reservoir completely empty" question from the other day—when I loosened the bleeder screw some air seeped out, and the fill level stick in the fill hole popped right up to about a 1/4" above the top.

Oh, and I've spent more time than I'd like the past two days wading into the holy war of coolant preferences. Puts the oil-choice controversy to shame. Good grief.

[CPHES]

In the end - during a cold winter - blue or green is ok - even mixed. Do not use dexcool - orange in color as a general rule, or Japanese - pink from what I have. I have 3 kinds of coolant in the garage. Flush and go Bmw 100% before the heat of summer

[geargrinder]

fill level stick in the fill hole popped right up to about a 1/4" above the top.

Don't overfill! The stick should be level w/ the top, not maxed out. A teeny overfill like that is fine but significant overfill will start to significantly raise your system pressure and increase chances of blowing things up. Lots of n00berz blow their cooling systems up prematurely because they think its supposed to be filled to the rim.

[chowza]

Late to respond here due to travel, but thanks and noted. Was trying to sort the coolant levels before I left, but now the car's sitting back on the East Coast for a couple weeks so I'll report back in January!