[=C=]

So I've had the unfortunate incident for my coolant expansion tank exploding open at the seam towards the windscreen side.

This luckily happened a minute or two after the car was turned off and parked in the garage so I wasn't stranded and car wasn't running.

At the time the temps were below the usual middle point, so I am unsure if the engine started to overheat after it was turned off.


- Is it possible that the thermostat failed closed at this point and caused overheating and higher pressure build up which blew the coolant expansion tank?

- I've checked for error codes with the COBB AP v3 and there was nothing relating to thermostat.

So could the thermostat fail closed without triggering any error code?


- Doesn't the coolant expansion tank have an overflow / safety mechanism to relieve any excess pressure in such an event?

[MightyMouseTech]

They fail all the time. Just replace the tank and keep driving.

[tisdrew]

The plastics get brittle and crack over time, same with hoses. Very common on older BMWs and cars generally.

Hopefully this doesn't confuse the issue further, but the electric water pumps in these cars continue to circulate coolant for 90 secs or so after the engine is switched off to help everything cool down. I doubt you had a thermostat failure. As MightyMouseTech said, you should be fine to simply replace the tank, refill/bleed, and keep going. Depending on age of adjacent parts, might be worth looking at the plastic piping and other coolant hoses as well as expansion tank level sensor.

[Jklad]

Originally Posted by tisdrew

The plastics get brittle and crack over time, same with hoses. Very common on older BMWs and cars generally.

Hopefully this doesn't confuse the issue further, but the electric water pumps in these cars continue to circulate coolant for 90 secs or so after the engine is switched off to help everything cool down. I doubt you had a thermostat failure. As MightyMouseTech said, you should be fine to simply replace the tank, refill/bleed, and keep going. Depending on age of adjacent parts, might be worth looking at the plastic piping and other coolant hoses as well as expansion tank level sensor.

How old was your expansion tank? Mine started seeping at the seam last winter after 145k miles, caught it before any explosions lol. Just replace and move on.

If you're up there in miles, good opportunity to replace other hoses including the hose that exits the bottom of the expansion tank, the upper radiator hose on the driver side that the skinny overflow connects to, and also the skinny overflow hose itself.

[=C=]

I'm 170,000~ Km's.
The water pump was replaced approx 15,000 km's ago but the thermostat wasn't replaced by the mechanic. This thermostat could possibly be the original unit on the car as I wont know since I bought this 2nd hand import from Japan to NZ 8+ years ago.

I am still concerned if it's possible for the thermostat to fail closed and I have no error codes showing up.


I've ordered a new expansion tank which includes the level sensor from FCP and also a thermostat with 3 aluminium bolts for the water pump.

I am thinking of replacing the thermostat as a precaution but would love to confirm if the thermostat is bung or if it's still Okay.

The piping all seems to be in OK shape.

[mweisdorfer]

Originally Posted by =C=

I'm 170,000~ Km's.
The water pump was replaced approx 15,000 km's ago but the thermostat wasn't replaced by the mechanic. This thermostat could possibly be the original unit on the car as I wont know since I bought this 2nd hand import from Japan to NZ 8+ years ago.

I am still concerned if it's possible for the thermostat to fail closed and I have no error codes showing up.


I've ordered a new expansion tank which includes the level sensor from FCP and also a thermostat with 3 aluminium bolts for the water pump.

I am thinking of replacing the thermostat as a precaution but would love to confirm if the thermostat is bung or if it's still Okay.

The piping all seems to be in OK shape.

Get the U shaped pipe that connects the thermostat & the water pump.

Remember where it's located. Next to two very hot turbos! Yep, I know it has a heat shield, but....

[Boland01]

Heat and cold cycles. Our 2007 335i had 94K miles when it cracked at the seam about a year ago. Replace the crossover pipe that connect to it too. They get very brittle.

[=C=]

Thanks everyone, will re-check the U-shaped hose and for now will replace just the expansion tank and re-bleed the system.

Since no codes are showing for the thermostat it must be OK.

I will run the car stationery to warm up and re-test if temp is at appropriate levels before deciding if I must replace the thermostat as well.

[roadkillrob]

I always do the cap on the expansion tank also (some come with it, oem doesn't) the tank gets brittle over time and the cap may increase pressure when failing and contribute to the problem, so i always do them as a pair as the cap is cheap.

[=C=]

Still waiting for the parts to arrive but noticed another problem.

That skinny plastic line that sits above the radiator and connects the coolant tank is actually snapped (probably when I was taking the coolant tank connector off and bent the rubber hose. That plastic piece above the radiator is so brittle that is immediately snapped off into multiple pieces as I tried to remove it form its mounting point. I am shocked that BMW used such plastic parts.

Anyway... NOW I need to replace that skinny plastic piece as well. I don't want to replace it with another plastic piece as over time the same issue will occur.
Item 14 on the diagram.
https://www.realoem.com/bmw/enUS/sho...diagId=17_0706


I'm thinking of using a straight copper brake line or fuel line instead of that OEM plastic piece to connect both ends. Any suggestions?

[=C=]

Not sure what others have done since I didn't get any reply, but I went ahead and ordered a 5/16 aluminium tube as a replacement piece, will be cutting and installing it tonight.

Still waiting for my coolant expansion tank to arrive, zzzz...

[oilcrankinject]

Pics?

[roadkillrob]

Originally Posted by =C=

Not sure what others have done since I didn't get any reply, but I went ahead and ordered a 5/16 aluminium tube as a replacement piece, will be cutting and installing it tonight.

Still waiting for my coolant expansion tank to arrive, zzzz...

If you search around others have done the same, some with stainless brake line, aluminum should work also.

[=C=]

Just an update in case anyone else comes across this. The 5/16 Aluminium piece was a perfect fix and should be a permanent solution to the original brittle plastic above the radiator.

Just did a simple barb flare on each end and the 2 original metal retaining clips grip the line tightly as if it was the original piece. Perfect!

New coolant tank arrived and installed without any problems. Also replaced the coolant cap as a precaution.

[feuer]

Originally Posted by =C=

..to the original brittle plastic above the radiator...

Line isn't plastic by the way, is aluminum coated with plastic

[=C=]

Originally Posted by feuer

Line isn't plastic by the way, is aluminum coated with plastic

No it's definitely plastic or brittle rubber hardened as plastic 90% of it.

Both ends at approx half an inch length where the metal clips hold the connection is aluminum... which seems odd why they didn't just use the entire piece as aluminium instead of the 2 ends. Crazy.

Sorry gents I didn't take any photos while doing this messy repair.

[feuer]

Originally Posted by =C=

No it's definitely plastic or brittle rubber hardened as plastic 90% of it.

Both ends at approx half an inch length where the metal clips hold the connection is aluminum... which seems odd why they didn't just use the entire piece as aluminium instead of the 2 ends. Crazy.

Sorry gents I didn't take any photos while doing this messy repair.

I have replaced many and seen that they are aluminum. Show us photo from where it broke off.

[techwhiz]

Originally Posted by feuer

I have replaced many and seen that they are aluminum. Show us photo from where it broke off.

Line #14 in his picture has been plastic for multiple cars I've replaced.
Just swapped one on my nephew's car and it was plastic. I replaced mine last year and it was plastic like the one I removed.

[=C=]

Originally Posted by feuer

I have replaced many and seen that they are aluminum. Show us photo from where it broke off.

14 Venting line radiator top 1 17127565094

consisting of black plastic tube and
rubber hose

https://www.realoem.com/bmw/enUS/sho...diagId=17_0706

[feuer]

Originally Posted by techwhiz

Line #14 in his picture has been plastic for multiple cars I've replaced.
Just swapped one on my nephew's car and it was plastic. I replaced mine last year and it was plastic like the one I removed.

I can't count how many I have replaced and have seen aluminum lining and could not bee only on the ends as =C= commented because these usually brake in the middle length

[=C=]

Reviving this old thread instead of starting another one.

I am hoping someone on this forum has the expertise and knowledge to be able to explain to me why my coolant expansion tank is constantly leaking coolant via the overflow port under the coolant expansion tank cap?

I can literally see coolant dripping through the overflow port out of the expansion tank and running down the tank when the car is at running oil temp and parked.
A few weeks ago I even replaced the cap again with another new BMW OEM cap and I am still seeing coolant leaking out of the overflow in the tank...
Last resort is to buy another new BMW OEM coolant expansion tank from FCP (again) and see if the issue repeats (again)...

I don't like wasting money replacing new parts with again new parts, so I would really appreciate the experts with knowledge to be able to explain to me why this is happening or if there is another problem in the cooling system I need to look at.


HELP!

[=C=]

Bump