[DavidXJ]

Happy New Year folks. Can I take advantage of your collective expertise, and reach out particularly to those who've been unfortunate enough to encounter the infamous coolant tank leakage issue... I realise this is one of the F90's few Achilles' heels. And having done my weekly wash today and while wiping out under the hood, I encountered this residue around the top of the coolant tank (see pics). I've not had a low coolant warning on the iDrive and the level of the fluid itself inside seems fine. But I'm worried that this might be evidence of a crack emerging of some kind, and I've heard reports that at its worst the coolant then leaks down into the injectors. So, I'd appreciate any gen. I'm going to try and get the car seen by the workshop as soon as poss, but I also have a week of commenting coming up so will need to use it!

[JayDD007]

Not all that uncommon of a problem as the tank sits in a very hot area of the engine bay. It’s one of the highest points in the cooling system so as long as you keep it topped off and don’t have the low coolant message the car won’t be starved of coolant. Definitely needs to be taken care of sooner rather than later due to it leaking onto all the bank 2 coils and plugs. I’ve seen multiple vehicles leaking bad enough to require replacement of these components.

[DavidXJ]

Originally Posted by JayDD007

Not all that uncommon of a problem as the tank sits in a very hot area of the engine bay. It’s one of the highest points in the cooling system so as long as you keep it topped off and don’t have the low coolant message the car won’t be starved of coolant. Definitely needs to be taken care of sooner rather than later due to it leaking onto all the bank 2 coils and plugs. I’ve seen multiple vehicles leaking bad enough to require replacement of these components.

Thank you. So, do you think the tank itself has a crack around the seam? To me, it looks like it's almost expanding and contracting--not really leaking too much, but maybe secreting residue or vapour (hence the crystallised spray/misting effect captured in one of my images).

D

[JayDD007]

Originally Posted by DavidXJ

Thank you. So, do you think the tank itself has a crack around the seam? To me, it looks like it's almost expanding and contracting—not really leaking too much, but maybe secreting residue or vapour (hence the crystallised spray/misting effect captured in one of my images).

D

Yes. The tank itself is leaking between the top and bottom halves, whole tank needs to be replaced.

[AHall]

Originally Posted by DavidXJ

Thank you. So, do you think the tank itself has a crack around the seam? To me, it looks like it's almost expanding and contracting—not really leaking too much, but maybe secreting residue or vapour (hence the crystallised spray/misting effect captured in one of my images).

D

Do you go for long drives or run the car hard? How long since the last time you checked the tank prior to finding this? What year is your car?

[DavidXJ]

Mine is a Feb 2020 build. I commute 120 miles twice a week, though haven't done that for a couple of months (and did mainly short drives till the New Year). But it has been cold here in the UK for the past fortnight, and the last time it was freezing I had a low coolant warning and needed to top up—but in that instance, didn't spot any signs of leakage. And no, I don't run it hard or rev it particularly aggressively, aside from the occasional spirited back road drive.

[pbonsalb]

There is not a consensus on the cause. The BMW TSB says the cause is “Chemical/thermal reaction with the plastic material of the expansion tank and coolant.” Subsequent to the 9/22/2022 TSB, BMW released an identical looking tank with a new part number that supersedes the old tank, but reports are that these new tanks have failed also.

Some of us think the problem is heat or pressure related. Either could cause the top and bottom halves of the tank to leak or the cap to leak. Some have bought the aftermarket billet tank that won’t fail at the seam due to chemical reaction, pressure or heat, but uses the stock pressure cap. I am curious to read longer term reports about cap leakage, if any, that would show that pressure is a problem.

There is also a replication kit that moves the tank off the top of the motor above the turbo and cat, but I think the purpose is to limit damage if the tank fails rather than to reduce heat or pressure. If the relocated tanks do well, it could be due to less heat or less pressure or a better design of the tank, which comes from a different BMW model.

I took steps to reduce heat in 2022, but have still noticed some white residue in the cap area. I will try to study the tank more closely in 2024. I may run the level on the low end of the range to see if that allows more room for expansion due to pressure. Pressure usually comes from heat so I am not sure I will make any headway. I have toyed with the idea of converting to Evans coolant, which I ran on my E90 M3 and which I run in my E36 M3, since it operates at a lower pressure, but it tends to expand a little more so it is recommended to run the level on the low side. It might also help with the chemical reaction explanation, assuming there really is something to it.

[Tiz113]

This is what mine looked like

Post i made about it along with a video from BMW tech below. There was a pinhole leak, most likley what happened with yours. BMW will replace under warranty

https://f90.bimmerpost.com/forums/sh...&postcount=235

[DavidXJ]

Originally Posted by Tiz113

This is what mine looked like

Post i made about it along with a video from BMW tech below. There was a pinhole leak, most likley what happened with yours. BMW will replace under warranty

https://f90.bimmerpost.com/forums/sh...&postcount=235

Looking at your video, and having looked at the place on the tank which seems to be secreting coolant again today, mine too appears to be a pin-prick hole, rather than a mid seam/join rupture which I originally thought was the culprit (given the way the coolant residue had run around and dried on the rim). And it's exactly the same place as yours, by the looks of it!

[Maxlude]

Originally Posted by DavidXJ

Looking at your video, and having looked at the place on the tank which seems to be secreting coolant again today, mine too appears to be a pin-prick hole, rather than a mid seam/join rupture which I originally thought was the culprit (given the way the coolant residue had run around and dried on the rim). And it's exactly the same place as yours, by the looks of it!

This is bad news to me
I was hoping that an unmodified S63TU4 in the UKs cool climate would be relatively immune from this.
Hope you get it sorted.
Do you have extended warranty?

[DavidXJ]

Originally Posted by Maxlude

This is bad news to me
I was hoping that an unmodified S63TU4 in the UKs cool climate would be relatively immune from this.
Hope you get it sorted.
Do you have extended warranty?

I'm hoping I caught it early enough before it got so bad as to cause any damage to the coils/injectors underneath. But yes, I've got third party extended warranty, but may not bother trying to reclaim through them if the parts plus labour isn't too hefty, since it'll speed up the process (extended warranty requires proof of diagnosis and a quote that then approve *before* any work is started) and I need the car back on the road by the end of the week.

[Maxlude]

Originally Posted by DavidXJ

I'm hoping I caught it early enough before it got so bad as to cause any damage to the coils/injectors underneath. But yes, I've got third party extended warranty, but may not bother trying to reclaim through them if the parts plus labour isn't too hefty, since it'll speed up the process (extended warranty requires proof of diagnosis and a quote that then approve *before* any work is started) and I need the car back on the road by the end of the week.

Ah yes the proof of diagnosis. I have occasional rear diff dust seal squeal when it's hovering around zero Celsius. It's a known fault .I took a video of it and you can hear it but they want the car to hear it themselves but it doesn't do it all the time, so I can't be bothered. It goes away after a couple of miles anyway.
I would have thought yours is clear cut with the residue visible?

[REF90]

Hello everyone - a very common question but was hoping to also get some input from the group. I ordered my M5 in 2019, love everything about this car and planning to continue keeping it for a while. I'm about to turn 40k miles. A few months back at 37,500 I asked the dealer to inspect the coolant tank (no visible residue) and they replaced it, saying it was starting to leak, with expansion tank 17-13-7-889-450. Tonight I parked in the garage, went back out an hour later and thought I could faintly smell coolant. I checked the tank and saw what might be coolant residue at the seams. Looks to be very slight compared to others, but curious if this needs to go back in and be replaced again already? Seems odd to only get ~2.5k miles out of the new tank. Appreciate the insight.

[fun2drv]

Yes, you may want to take it back and have them do a pressure check.

Good luck!

[AHall]

I would take it back in for sure. I wonder if BMW has contacted the manufacturer of the tank, Heyco Germany, to inform them of this issue. Heyco may have an opinion on the failures many owners are experiencing. Unfortunately it does not appear BMW is going to do anything to solve this problem.

[REF90]

Just following up on the above - went in for service today. They replaced the cap, pressure tested the system, and said everything was good to go. They also left the coolant residue that was on the tank and said it was traced back to the cap. Needless to say I'm a little skeptical of this. I'll clean the tank and keep an eye on it to see if any new residue shows up, but curious if there could still be an issue despite the pressure test?

[pbonsalb]

I think coolant released from the cap goes down the cap drain channel and onto and into the horizontal tank seam and travels around. While some have reported pinhole leaks in the tank, others may just be seeing residue from a cap release. REF90 wrote that the tank was pressure tested, so it is not leaking, at least not at the test pressure. I presume the test was at or beyond the cap pressure — 200kpa or 2 bar or 29 psi. So why are the caps leaking? Are they defective? Is coolant pressure sometimes exceeding the cap release rating?