How To Remove and Replace Coolant Expansion Tank on BMW 335i

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The radiator overflow tank serves as the reservoir for engine coolant that is heated to its boiling point and would otherwise rise up and out of the radiator. Working in conjunction with a thermally activated spring built into the cap, the overflow tank creates a closed cooling system that is much more reliable and practical than previous designs. As the temperature and pressure rise to the coolant's boiling point under pressure, the cap spring activates and allows the heated liquid to flow up and into the overflow tank. The fact that the system is under pressure means that the liquid reaches a higher temperature before boiling, further increasing the effectiveness of the system.

If you had a low coolant warning light , the expansion tank may be one of the parts of the cooling system to blame.

If you work on any cooling parts, including the expansion tank, you must bleed the system/purge. Bleeding the cooling system involves removing trapped air that can clogg the radiator, water pump and so on. Trapped air can cause hoses to burst and also fail the expansion tank or blow head gasket . Reasons that a low coolant warning needs immediate attention.

Work notes:
Trapped air will have heater core blow cool air when temp is set at high. If you notice this repeat steps. Wait for engine to cool and "bleed the system"
1. fan on low heat on high
2. Add coolant to indicated marks never over fill
3. you can leave cap off or bleeder off to watch for bubbles purging
4 place cap back on start the vehicle
5 if you still have bleeder on ...release it and let the air out( you may lose a little coolant)////if you released bleeder before starting , wait for bubbles to go away...you may still lose a little coolant doing it this way....both ways work the goal is to remove trapped air out the system.

There is also an electronic way to bleed the system activating the electronic water pump so it can run itself to purge the cooling system of trapped air. This will allow you to bleed the system with out spilling any coolant. A battery charge would also help. The reason for the battery charger is to prevent the battery from draining while the water pump is activated. there would be no need to start vehicle with this method. ...I may do a video on this in the future.

6. Good idea to watch coolant temp in hidden service menu but not really required when the goal is to remove trapped air. You will know when your vehicle reached normal operating temp when fan is on. Hidden service menu ...coolant temp access:

7. Drive vehicle and make sure you heater works and you should be all set. If its blowing cold air then air is trapped in cooling system. At that point bleed system again.

8. Good idea to bleed system on an incline rather flat surface ....30degree jack stands or a slope really does help, but not required.

Use Bmw coolant with distilled water 50/50 mix
Good idea to use a coolant funnel even tho I did not in this video...this will prevent overspray of coolant.

Thank you for watching #bimmajoc #bimmergurus #Raoul #Jacques

[Bmwguy]

Thanks for being so detail oriented and methodical. So many on here leave out critical steps assuming that the viewership knows everything. If we did, well, we wouldn’t be watching.

[rodneystewart]

My man, thanks so much for this video. I did this job yesterday on my 2006 330i. Two issues I ran into. Upper hose didn't fit snug on new tank (purchased from BMW) resulting in coolant spraying everywhere when I started the engine. So I used some plumbers tape around the tank threads and that solved that problem. Second was with the bleeder. Was hard to tell when bleeding was fulling complete as still had some coolant coming out through the bleeder after the bubbling stopped. I closed the bleeder, checked the heater and it was working and blowing hot air so figured I was straight. Coolant level was fine when I checked later. By the way, I have an electric water pump and didn't do the other procedure with the car off and external battery attached, etc. I hope that doing it your way in this video is fine since car is blowing hot air 🤷🏾‍♂. Thanks again.

[sridharmd]

Just installed a new tank today on a 2007 BMW 335i. Shop quoted $350, I bought the tank off eBay for $38 so saved $312. Dealer cost is probably much higher.. Thanks Bimma for this post !!!

[kciracheta]

Awesome I followed your steps, and I was able to replace it with no problem, I have zero experience working with cars but you made it very easy by this video!!! Thank you!!

[guestwho]

Best n55 diy video on coolant tank replacement. Better than all the others that popped up on my search.

[marckodiak]

Excellent video, great job of breaking it down Barney style, knocked this out in 15mins

[moniquea]

This was really helpful! Had to empty out my coolant expansion so this was really easy to follow along with and the detailed instructions and shot made it so easy. Thanks heaps!

[twodutch]

Much Respect I did this Job in 45 Min including testing Thanks

[AD]

I just swapped mine. You have way more room because I have the 2 vacuum boosters in the way. Getting the bottom hose off and on was a little tricky. Thanks for the video. You helped a lot. God bless #N54 #E93 #BMW #335i #SanDiego

[BLackPEsa]

You were a big help for me today man. I was stuck and you can through man. Keep posting more videos. New subscriber

[MIGUELZGA]

Good job bro on explaining the steps.. really helpful, really needed that👌🏻👍🏻!

[ale.sativadivaa]

Where did you purchase your new coolant expansion tank?

[angle]

ok so I did this no leaking anymore but now a engine malfunction popped up, how do I fix that it was just the expansion tank nothing else was touched

[startingtech]

thought this was an electric bleeding procedure where you hold pedal for 10 seconds and it activates the electronic bleeding

[umufella]

Thank you for this vid. Helped a whole bunch

[kingly]

Good video I'll be using this next week when my parts come in. Got a similar leak, right along that seam. I still have pressure in the system though when i uncap, and the coolant level isn't down much (haven't had a low coolant light). You think it's ok to drive? Assume I've been driving for a minute already with it like this...

[othmanounekal]

Hello there,
Thanks for the video it’s really helpful just one question pls after changing it did you have any smoke coming out of the engine while you driving cos I changed my one and after 2 days I took it for drive I put my foot down and I realised it was smoke coming out from the engine when I open the bonnet it was around the coolant tank area but it wasn’t leaking at all, do you think it’s the excess anti frizz that spilled while I was changing it and bleeding it or something else? Thanks

[marcosantana]

Excellent video question if am installing a new radiator and a new expansion tank can I bleed the system once after installing the two parts?

[Minhlacey]

Just did mine. Thanks for the video bro.

[johnvigil]

do you know if you can replace the coolant level sensor without draining and removing the expansion tank itself? I have looked and I can't seem to find any details on replacing just the level sensor