Hello Gents! I'm new here but I moderate on a non-BMW car forum so I'm excited to get started here! I'm the proud new owner of a 2000 Carbonschwarz M5. It is replacing my E46 that burned down courtesy of a buggered LCM. The 3 series was fun and very easy to work on but didn't quite have the fun factor that I have with some of the other cars. The fire was a blessing is disguise!
The car had SES codes for the SAI system and low coolant temp. Some computer work fixed the SAI and the low coolant code was the same one I had on the E46 when I got it. I'm posting in this thread because it was the one I found first when googling the E39 thermostat info and I had some issues with the O-Rings I wanted to share.
This first photo is what the the new ring on the tube should look like. It should be tight and you should not be able to push it from side to side in its groove.
This is what it shouldn't look like. See how it bulges out on one side when it is pushed from the other side?
I am not squeezing it hard at all in this photo - just holding it snug on one side while the ring bulges out on the other side.
I split 4 of these (I bought 8 instead of the minimum of 4) trying to install the thermostat before I went to the local BMW dealer and got the correct size shown in the first photo. Here is a 'wrong' O-Ring next to one of the OEM BMW rings I picked up at the dealer:
Once I had a correct fitting O-Ring, it popped in the first time and sealed perfectly. I bought the first set of parts from one of the vendors mentioned a lot on this site. I don't want to mention who because they were extremely responsive when I contacted them. They say they only receive Genuine BMW parts also and are researching a potential lot problems. They refunded my purchase and reimbursed me for the Blue BMW Cool-Aid lost during the failed attempts. In short, mistakes happen and they handled it perfectly.
The moral of the story is if the O-Rings are loose (popping out the side) when you try to install the thermostat side, you have zero chance of getting the engine side in without at least one of them popping out and splitting.
Another top tip is to buy or rent a radiator pressure tester. Because of how far into the engine these go, you can't tell they are leaking until you do a heat cycle which means you have lost a bunch of coolant and spent a bunch of time on R&R for the VANOS lines and intake. It is much nicer to pump up the system with air and make sure it holds before you finish reassembly and pour in your $25/gal magic juice.
I am almost done with the first layer of triage on the car. SES light is out and emissions have been passed. I've done some simple things like replacing a broken window regulator, a broken fog lamp and the struts for the trunk lid. I'm tracking down the mystery of the stability/ABS/Brake triad currently and then will move forward on some more somewhat elective maintenance items. I also need to install my AL Priority/9500ci... soon. As you all know, this car would much prefer to gallop along at twice the legal speed limit.
I've read Alex Roy's book and I don't carry bail money in cash like he did. Better get the other countermeasures set up!