Expansion Tank And Holder - Please Help

[Jay Kay]

Having just been recovered from the M1 after my expansion tank splitting itself in half, I have got home and removed it. I noticed (and I may have done it during removal) that there is what looks like a spring loaded sensor in the hodler underneath it. Unfortunately the tabs that hold the sensor in place have snapped and it is now hanging out on the spring. I am going to order a new tank but does anyone know if I will also need a new holder? Replacing it looks a far bigger job as power steering cooler etc also seems to sit on it.

I wonder if it matters that the thing isn't held in as once the new tank is sitting on top of it, i assume it cant move. I do know that some car parts are held in place purely to make fitting other parts easier. I know that sounds daft...

Anyway if anyone knows I would appreciate the help.

Many thanks

[Guest DazH]

Yes, seems to be quite a common fault on the E46s with the all in one rads. I usually don't use the phrase "Common fault" but damn, have i had to change alot of those...

the sensor you are refuring to is the coolant temp sensor. Try not to break it as it's pretty pricey. If the clips holding it to the tank are shot then you need to replace the tank as you have already discovered.

Not 100% sure, as in i can't picture in my mind, what you mean by this spring thingy. Get the new tank in and post a pic up here if need be

Daz

[Jay Kay]

Thanks Daz

I did some reading and it transpires that it is the transmission cooler thermostat which sits between the expansion tank and its holder. The manual cars dont have them just the autos. supposedly they are a good idea as the thermostat opens to allow warm coolant to circulate the box, getting it up to termp quicker and then closing it off once at temp to keep it there rather than just getting hotter and hotter. While in theory its clever, in practice BMW made the tank virtually imossible to remove without snapping the plastic holder at the bottom. I googled it and there are countless threads from numerous countries all saying the same.

I have ordered a new expansion tank and thermostat from BMW, coming in at £79 - each. I did consider ditching the thermostat, as again there are numerous threads on the net about how they are not needed as long as you're not doing redline gear changes from cold, however I swear by the mantra that it must be there for a reason.

Parts come tomorrow so i'll get on it after work. Just need to do a bit more reading about how to bleed the system when I'm filling it up.

[Jay Kay]

In case it helps anyone, ignore all the videos on youtube about how to bleed the system, they are virtually all wrong. People running the car with the cap off, constantly opening and closing the bleed screw etc. All they are doing is introducing air into the system. Its actually far easier than I thought to fill up the system from scratch. Just take out the bleed screw and with the heater on max temp but engine not running, slowly fill up the system until coolant comes out of the bleed screw with no air bubbles in it. Put the bleed screw back in, put the cap back on the tank and away you go. None of this bleeding air our while its running rubbish. After a 5 min drive, check coolant and top up in needed and your done.

[Guest DazH]

In case it helps anyone, ignore all the videos on youtube about how to bleed the system, they are virtually all wrong. People running the car with the cap off, constantly opening and closing the bleed screw etc. All they are doing is introducing air into the system. Its actually far easier than I thought to fill up the system from scratch. Just take out the bleed screw and with the heater on max temp but engine not running, slowly fill up the system until coolant comes out of the bleed screw with no air bubbles in it. Put the bleed screw back in, put the cap back on the tank and away you go. None of this bleeding air our while its running rubbish. After a 5 min drive, check coolant and top up in needed and your done.

The bleeding process of a 6 cylinder bmw is much debated over within the community.

With the bleed screw CLOSED, running the engine will push air trapped in the system up into the expansion tank and out of the engine. If it's a fully flushed system (not only from the rad but from the block screw under ex mani) you will see air bubbles. LEaving the bleed screw OPEN whilst doing this, will potentially drag air in.

Been doing it this way for many many moons.