[lllRazorlll]

Bumping this thread in case anyone else noticed this or has any reasoning for why this happens

[Ed CT]

Even though I've only had this F32 since Oct2025, the issue has alredy gotten my attention. First, with 2 low coolant warnings followed by 2 top ups. Then a drain & refill and a water pump replacement. Then a few puddles under the engine.

So far, I'm seeing two symptoms: gradual coolant loss with no leak seen, and coolant spews with puddles on the ground (outlets yet to be found). The sudden coolant spews have both been when temps were down in the teens and single digits (F) and after a drive. After the last three drives, I'd loosened the exp tank cap shortly after parking to relieve the pressure, and then put the cap back on. So far, no puddles.

Both of these symptoms could be from the same root cause - maybe a weak seal that weeps & evaporates in cool or warm temps, but gives up totally due to contraction when very cold.

It's been so cold here in the northeast that I'm not inclined to work on the car, even in the garage. But I'm subscribed to your thread here, and will be keeping up on this issue and will report any findings.

[lllRazorlll]

Originally Posted by Ed CT

Even though I've only had this F32 since Oct2025, the issue has alredy gotten my attention. First, with 2 low coolant warnings followed by 2 top ups. Then a drain & refill and a water pump replacement. Then a few puddles under the engine.

So far, I'm seeing two symptoms: gradual coolant loss with no leak seen, and coolant spews with puddles on the ground (outlets yet to be found). The sudden coolant spews have both been when temps were down in the teens and single digits (F) and after a drive. After the last three drives, I'd loosened the exp tank cap shortly after parking to relieve the pressure, and then put the cap back on. So far, no puddles.

Both of these symptoms could be from the same root cause - maybe a weak seal that weeps & evaporates in cool or warm temps, but gives up totally due to contraction when very cold.

It's been so cold here in the northeast that I'm not inclined to work on the car, even in the garage. But I'm subscribed to your thread here, and will be keeping up on this issue and will report any findings.

Where is the coolant spilling on the ground? If it's on the left side it could be your oil filter housing as it is a known failure point on this engine

[Ed CT]

Two of the three puddles were pretty much in the center, the other was off to the right and front, which surprises me (altho it could have been the way I parked). I suspect that the coolant spilled onto the engine shield and exited to the ground thru the oil plug hatch.

My next move is to remove the underbelly shield, take a good look for leak evidence, clean things up, go for a ride, and then up on ramps to take a look again for leaks.

[lllRazorlll]

Originally Posted by Ed CT

Two of the three puddles were pretty much in the center, the other was off to the right and front, which surprises me (altho it could have been the way I parked). I suspect that the coolant spilled onto the engine shield and exited to the ground thru the oil plug hatch.

My next move is to remove the underbelly shield, take a good look for leak evidence, clean things up, go for a ride, and then up on ramps to take a look again for leaks.

I would do a pressure test and look for the leak

[darkfires102]

Every German car I've owned with this sort of expansion tank system does this. The cap is the main culprit for evaporative losses + the high norm operating temp of 230F. I always just top off a couple ounces every oil change. Replacing the cap helps but it's just going to happen again in a year.

I would also replace the plastic bleeder screw with a brass one.

[lllRazorlll]

Originally Posted by darkfires102

Every German car I've owned with this sort of expansion tank system does this. The cap is the main culprit for evaporative losses + the high norm operating temp of 230F. I always just top off a couple ounces every oil change. Replacing the cap helps but it's just going to happen again in a year.

I would also replace the plastic bleeder screw with a brass one.

I replaced the expansion tank cap and bleeder screw with new genuine parts. I haven't noticed any residue around the filler neck or threads. Someone even suggested coating the filler neck, threads, and o rings with silicone grease to prolong the cap.

I haven't noticed any coolant loss of this kind on my 435i when I owned it.

[gantona]

Originally Posted by Ed CT

Even though I've only had this F32 since Oct2025, the issue has alredy gotten my attention. First, with 2 low coolant warnings followed by 2 top ups. Then a drain & refill and a water pump replacement. Then a few puddles under the engine.

So far, I'm seeing two symptoms: gradual coolant loss with no leak seen, and coolant spews with puddles on the ground (outlets yet to be found). The sudden coolant spews have both been when temps were down in the teens and single digits (F) and after a drive. After the last three drives, I'd loosened the exp tank cap shortly after parking to relieve the pressure, and then put the cap back on. So far, no puddles.

Both of these symptoms could be from the same root cause - maybe a weak seal that weeps & evaporates in cool or warm temps, but gives up totally due to contraction when very cold.

It's been so cold here in the northeast that I'm not inclined to work on the car, even in the garage. But I'm subscribed to your thread here, and will be keeping up on this issue and will report any findings.

From my perspective you should not bleed the pressure when engine is hot (opening the cap). It will allow water to boil, creating air pockets everywhere on the coolant circuit.
Then, next time hot, you will lose coolant by the pressure cap doing its job.

That’s being said, I had to fill up one time, recently at 150k km.
I did full coolant flush at 120k km.

I have no idea where it leaks, if it is…

[Ed CT]

Originally Posted by gantona

From my perspective you should not bleed the pressure when engine is hot (opening the cap). It will allow water to boil, creating air pockets everywhere on the coolant circuit.
Then, next time hot, you will lose coolant by the pressure cap doing its job.

That’s being said, I had to fill up one time, recently at 150k km.
I did full coolant flush at 120k km.

I have no idea where it leaks, if it is…

Yes, sound advice. I waited about 20 minutes before pulling the cap. It was really an experiment to see if relieving any residual pressure would prevent the coolant spew under the car when we got frigid temps - so far, 3 for 3 on no spews.

[lllRazorlll]

Originally Posted by gantona

From my perspective you should not bleed the pressure when engine is hot (opening the cap). It will allow water to boil, creating air pockets everywhere on the coolant circuit.
Then, next time hot, you will lose coolant by the pressure cap doing its job.

That’s being said, I had to fill up one time, recently at 150k km.
I did full coolant flush at 120k km.

I have no idea where it leaks, if it is…

Originally Posted by Ed CT

Yes, sound advice. I waited about 20 minutes before pulling the cap. It was really an experiment to see if relieving any residual pressure would prevent the coolant spew under the car when we got frigid temps - so far, 3 for 3 on no spews.

Have you guys also noticed this behavior where coolant top off is just normal?

[freakystyly]

I hadn't checked my main reservoir in months due to winter and forgetting...

Last night I added about 125ml (1/4 of a water bottle) to get back to minimum. Small reservoir still holding the same. Approx 115k kms on the clock.

Side note, about a year ago I had replaced the caps and lubed the thread with silicone. They're much easier to unscrew vs un-lubed.

[Ed CT]

Originally Posted by lllRazorlll

Have you guys also noticed this behavior where coolant top off is just normal?

Not enough data points for me, since I've only had the car since Oct 2025. But one of the first things I did was check the coolant level, and it was maybe 1/2" to 1" below the min marker, so, I left it as-is, since I normally keep expansion tanks slightly below min. A few hundred miles later, I got the "Low Coolant" warning, with no signs of a leak at that point. This saga is ongoing, though, with having replaced the water pump and then a few coolant spews to the ground. I'm determined to find the cause - when our good old fashioned New England winter ends.

[lllRazorlll]

Originally Posted by Ed CT

Not enough data points for me, since I've only had the car since Oct 2025. But one of the first things I did was check the coolant level, and it was maybe 1/2" to 1" below the min marker, so, I left it as-is, since I normally keep expansion tanks slightly below min. A few hundred miles later, I got the "Low Coolant" warning, with no signs of a leak at that point. This saga is ongoing, though, with having replaced the water pump and then a few coolant spews to the ground. I'm determined to find the cause - when our good old fashioned New England winter ends.

I had the same thought process as you. Keep the level halfway between min and max because I felt like at max, the pressure would be too high. I looked inside the tank last week and saw the height to where the fluid level rises to, denoted by the walls of the tank being wet, being quite a ways from the cap. It then clicked for me that the cap acts as a venting mechanism. I topped off to the max line and am now just monitoring it. At the end of the day, I'm not an engineer and it's me vs. an entire company with millions/billions of dollars of R&D

[lllRazorlll]

I just did an oil change 500 miles ago and I topped off the high temperature circuit reservoir. I have been using the climate control from time to time and noticed that my level is now 70% of the way between the min and max marks on the level inside the tank.

Before the oil change, I topped off the tank and put about 1700-1800 miles and seldomly used the climate control and noticed a slower rate of coolant consumption.

I definitely think there is something related to running the climate control and the coolant leaving the high temperature reservoir

[freakystyly]

Mine still needs topping off during winter (no AC) and heater on... in theory it should be colder on that circuit? I also rarely use the AC in the summer and just run windows down. Nearly the same consumption.

For me it's just a slow losing battle and I have a jug of coolant ready. I've never been asked for coolant yet, even when below min.

[Lu Bu]

For my circumstance, the issue ended up being the water pump. I also decided to replace the reservoir caps at the same time.

https://f30.bimmerpost.com/forums/sh...6&postcount=71

I've been monitoring the coolant levels skeptically since, and so far, they have resided just under the maximum line. I decided to fill up a glass bottle with coolant and store it in the trunk, just in case.