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First I wanted to say thanks for all the hard work on this. I am about to undertake this on my 2001 330Ci among other things like replacing all the heater hoses (under the hood of course--not inside the cabin...I have no desire to mess with the heater core), CCV, leaking power steering pump + hoses, oil leak (definitely leaking because of the oil pan gasket, but I am going further to replace the oil filter housing gasket too), and also fuel filter.
One of my main concerns and questions lies with the transmission cooler. This is quite new to me as no car I have ever owned has one of these...well, frankly I have never owned a BMW before...so this is my first. I am wondering, if I replace the O-rings on the hose going into the transmission and also generally, if I disconnect the hoses from the cooler itself and the cooler from the radiator...what kind of fluid am I expecting to drain from both of those hoses?
I am assuming one is a intake and one is a return hose and that it is coolant that will spill from the hoses should I choose to dissemble it completely--meaning I detach it from the transmission and also from the radiator and the trans cooler itself. I noticed you described having a bucket to catch the coolant. What confuses me is the Bentley manual says transmission fluid. I think I asked one of the sales' guy at Tischer and they said they think transmission fluid will come out.
Seeing how I bought into this vehicle at 98k without knowing the history--yes I know my bad...I should have done more homework, but alas the mistake has been made and now I have to just go with it. In any case, I have read around that the transmission fluid is really a picky thing with these BMW transmissions...well that is a little bit of a misnomer, since there would either be a GM made tranny or ZF in these e46'ers. Mine is a ZF. I read somewhere on the forums and it seems logical that if a transmission was not cracked open at 30k, then just leave it alone...I wouldn't want it to die on me. I also see that the refilling procedures for it is really particular too--must be within a certain temperature.
So I am unsure and would not want to mess with the transmission fluid if I did not have to...so I was wondering when you did this DIY did you replace your O-rings? Did you disconnect the pipes from the tranny? With this big maintenance overhaul that I am doing, I am trying to replace any rubber O-ring, anything rubber, and plastic so that way I get my next 100k miles of maintenance free headaches (cept for oil, gas, and your standard fluid changes. I never want to have to go replace gaskets anymore...if it is the head gasket, I'd probably either attempt it if I had another car (which I do now, but I think I might sell it after I fully fix all the leaks in this bimmer) or I would just get another engine.
From an engineering point of view, I would have designed the transmission with an input channel and output channel for coolant to flow through; hence if detaching those hoses, I would have to say it should be coolant that flows from those hoses and the transcooler itself. Can you verify that I would have designed this correctly--and also BMW did the same?