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Discussion Starter #1
Hi all,

Does anyone happen to know what size the O ring is in the bottom of the radiator expansion tank? 22 x 3.5 keeps cropping up on forums, but I'm sure there was two in there but can't remember for sure? Ever since I replaced the tank a few years ago it has given me grief from time to time, its an aftermarket one from ECP, forget which brand. Last year it was leaking and so I removed it and noticed the O ring appeared a poor fit. They didn't sit slightly proud of the grove so weren't biting onto the spigot to form a seal. Anyhow I took them to a local engineering supplier and they said it looked an odd size. He gave me one with a slightly thicker cross section, but I would say they were a bit too thick. Any ideas? Also, is it worth stick a bit of RTV sealant in there as well, or does anyone have any other tricks up their sleeve? I've been tempted just to buy a new bloody tank but an original coz I'm sick of draining and pissing about with the sodding thing!!

Any help much appreciated.

Andy
 

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I had loads of bother with the o-rings in mine until someone on here told me to grease them. White lithium is best but anything will do, it helps the o-ring into place and to seal properly.
 

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Discussion Starter #3
Just got home and noticed some hissing and dripping. Popped bonnets and bloody expansion tank has cracked. It's not that old either, just over couple of years. Sod it, I'm going to pay through the nose and get a BMW one. ECP do a Hella one (this mine is an EIS) but there's plenty on forums complaining about those as well. At £86 its more than double price but worth it if it finally puts this to bed, that driveway is getting colder by the day!!
 

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Discussion Starter #5
Job done, new BMW expansion tank. Noticed a bit of play on the water pump bearings so I've forked out for one of those too, albeit a ECP one. New aux belts for good measure. I can see why people have issues with aftermarket expansion tanks leaking from the bottom, the o ring cross section ain't thick enough, they barely sit proud of the groove they sit in. BMW don't sell them separately either and they are an odd size. The local engineering supplier I went to had boxes full of o rings but couldn't find the exact size. If you are buying an aftermarket expansion tank, have a look at the o rings, if they don't sit nice and proud of the groove they won't bite onto the pipes and will very likely leak so i'd hand it back. I used a bit of vaseline to assist fitment (vaseline is the girlfriends property btw, just though i'd mention that small fact). Bled system up which was a pain free task surprisingly. Hopefully all set for winter now. Just the 335d to sort which is getting new thermostats (can't get past 82 degrees) new glow plugs and controller. Now officially skint

20161103_122801_resized.jpg
 
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It just not only o rings also where o ring is placed : is too deep or too big.
Even you think is not leaking, under driving hoses will move a little bit.
Then it will leaking again, after this issue I have swore to myself no more aftermarket cooling tanks.
 
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