M50i / N63B44TU3: Coolant loss / evap?

01-03-2024

Apologies for cross-post but the X7 community is more concerned with software problems of the new iD8.5 rather than good ole mechanical problems.

2022 X7 M50i Owner:

Since I’ve had the vehicle (29K miles), I have had the “Low Coolant” Warning come on twice. Both times occurred in cold winter/January and both times I topped it off with a minimal amount (about 100-200ml / 8-10oz maybe). The first time was at about 14k miles and exactly about 15k miles later the second time.

I do see some minimal crystallized crust around the coolant expansion tank cap. It is the tank on the right side of the N63 engine that goes low, the one in the center front of it stays super level.

The service advisor said the tank on the right is the one for the turbo cooling. He also said that such a minimal amount of coolant use is normal with these engines due to the extreme heat at the turbos.

What is everyone’s thoughts? Drive it and don’t bother, keep topping off when necessary? Or make an appointment and have the dealer chase a potentially super minimal leak that would hardly show up on a pressure test.

01-04-2024

My car has 29000km (18k miles). A low coolant warning came up at 15k miles. It appeared maybe 3 times in a span of 2 weeks, only in the mornings during a cold start.

When I finally brought it to the dealer, they topped it up and said it was normal. It sounds like I should be expecting this to happen again in due time.

01-04-2024

I'm gonna disagree that coolant loss is "normal". The cooling system is sealed, hence it's ability to not boil above 212F. That means that the coolant isn't just evaporating/boiling off. It's going somewhere outside of the system.

That said, it may be typical of a poorly tolerances o ring or something like that, but it's not "normal" in that it's designed to do that.

All that said, it may be tough to get the SA to help if they think it's normal. Ask for a technical explanation and not "because the turbos are hot". They won't be able to provide it and then maybe you can use that to convince them to have a mechanic look at it.

01-04-2024

BlkGS wrote
I'm gonna disagree that coolant loss is "normal". The cooling system is sealed, hence it's ability to not boil above 212F. That means that the coolant isn't just evaporating/boiling off. It's going somewhere outside of the system.

That said, it may be typical of a poorly tolerances o ring or something like that, but it's not "normal" in that it's designed to do that.

All that said, it may be tough to get the SA to help if they think it's normal. Ask for a technical explanation and not "because the turbos are hot". They won't be able to provide it and then maybe you can use that to convince them to have a mechanic look at it.

I believe there’s a YouTube video about this . A guy talks about the expansion tanks, and what to do type in that engine number with Coolant loss

01-04-2024

swainbmw wrote
BlkGS wrote
I'm gonna disagree that coolant loss is "normal". The cooling system is sealed, hence it's ability to not boil above 212F. That means that the coolant isn't just evaporating/boiling off. It's going somewhere outside of the system.

That said, it may be typical of a poorly tolerances o ring or something like that, but it's not "normal" in that it's designed to do that.

All that said, it may be tough to get the SA to help if they think it's normal. Ask for a technical explanation and not "because the turbos are hot". They won't be able to provide it and then maybe you can use that to convince them to have a mechanic look at it.

I believe there’s a YouTube video about this . A guy talks about the expansion tanks, and what to do type in that engine number with Coolant loss
Could you help me find it? I searched for a while and can only find previous-gen N63 related content.

01-04-2024

Tr4ckD4ys wrote
Could you help me find it? I searched for a while and can only find previous-gen N63 related content.

I would need to watch again but I believe it’s the bottle

01-04-2024

BlkGS wrote
All that said, it may be tough to get the SA to help if they think it's normal. Ask for a technical explanation and not "because the turbos are hot". They won't be able to provide it and then maybe you can use that to convince them to have a mechanic look at it.

I didn't question my SA last time but if it happens again, I'll definitely be questioning him about the coolant loss. It was my first experience, but the OP had it happen 2 times already, both around the same interval. So it's definitely a concern. :thumbdown

01-05-2024

some coolant lost definitely NOT unusual. As much as everything is sealed, nothing is perfectly seal, specially the expansion tank. All mine lost a bit in a while. And BMW, in fact all car brands, sell coolants to end user for reason.

Number here matter, 100mL is 3.4oz. A can of coke is 12oz, so 1/3 of a can of coke, this is kind of normal. Now 10oz is approach a can of coke, it is a bit much. so which one it is?

Also, beside some crystallization, which is normal, do you see coolant anywhere under you car? And if you open hood when ICE is running at operation temperature, can you smell coolant?

01-05-2024

All of my recent BMWs lost a little coolant as well, starting with a 2016 X3 and more recently a 2020 X1. As a result, I've added a reminder to check them and top-off every 15K miles. The X5 will hit 15K miles this summer, and I'll check it at that time. They've needed anywhere from 0.5 cup to 1.25 cups to bring them up to the minimum levels at that 15K interval. My 2018 GTI just needed a top-off for the first time, but at 60K miles it only needed 0.75 cup - and I was planning on doing a coolant flush soon anyway. I miss the old days when I could do a coolant flush on my BMWs every 30K miles! Now they don't recommend a coolant flush ever - preferring to wait until something like the electric water pump or thermostat fails.

01-05-2024

Same persistent problem with my 2020 X6 M50i
Decided to move on from it rather than possibly have to deal with a major unwarranted engine issue

01-05-2024

eelnoraa wrote
some coolant lost definitely NOT unusual. As much as everything is sealed, nothing is perfectly seal, specially the expansion tank. All mine lost a bit in a while. And BMW, in fact all car brands, sell coolants to end user for reason.

Number here matter, 100mL is 3.4oz. A can of coke is 12oz, so 1/3 of a can of coke, this is kind of normal. Now 10oz is approach a can of coke, it is a bit much. so which one it is?

Also, beside some crystallization, which is normal, do you see coolant anywhere under you car? And if you open hood when ICE is running at operation temperature, can you smell coolant?

Agreed 100%. A little seepage out of the expansion tank is normal, most of the time that's just a hose to a barb connection. A lot of expansion tanks aren't totally sealed either, or have a run off to an overflow tank, etc.

A little coolant over the years, sure. 100mL in a year is higher than I've experienced on America cars, but different brands have their strong and weak points. American cars typically focus a lot on not leaking fluids, whereas German cars appear to prioritize other things.

10oz in under a year on the other hand is kind of a lot, and I'd be looking for the problem. It could be something as simple as a loose hose clamp on the expansion tank. Maybe a pinhole in a hose that only opens up when it gets hot enough. Either way, it's enough to warrant checking into.

03-06-2024

I think there could be some misinformation here. To my knowledge the center cap is the one that provides coolant to the turbos. I believe this reservoir gets replenished by the main tank which is on the right.

I got the low coolant warning last November - it was intermittant but I bought a jug of coolant from BMW ($65 by the way), and I topped off the fluid, taking 5 plastic cups to fill (estimated at a quart). Yesterday morning I measured again (since I was taking it for service) and it was quite low once again. When I took in my 2021 M50i, they pressure checked (finding no leaks) and topped it off again. So loss of a quart last November and another quart down since then.

I was told this was considered normal but I have a hard time believing that could be true (unless the turbos are actually buring up this coolant). Still it's alarming to be sure.

My M50i is nearly three years old now with about 23K miles and I never had this coolant loss before last November. So I feel it could be a long term problem. I plan to send a letter to BMW to document my findings on what seems like an extreme loss of coolant.

05-21-2025

JimVR4 wrote
I plan to send a letter to BMW to document my findings on what seems like an extreme loss of coolant.

As someone who had experience with multiple BMW dealers and BMW North America, I couldn't resist laughing at this intention. BMW NA doesn't care at all, they sell cars to dealers and their interest ends there. BMW dealers never invest time into time consuming labor that doesn't show up as a check engine light, because BMW NA has lower labor rate for warranty repairs and dealers won't make money by spending hours inspecting every inch of the engine bay. They usually say "works as expected", "not able to reproduce".

Having said that, it is normal to have a minor coolant loss over a year, same as the oil. Dealers top everything once a year. Coolant may evaporate through the expansion tank cap. Some models have 1.4 bar cap with 140 on the cap which means 140 kPa, others have 2 bar or 200kPa. BMW turbo engines are very hot. The permissible coolant temperature can go as high as 108°C/226°F in Economy mode, this allows the metal to expand as much as possible to reduce friction. It may go even up to 117°C/242°F until protection kicks in. At this temperature the diluted water may evaporate and if the internal pressure reaches the cap pressure limit the excessive pressure will go out through the cap. They even have pressure equalization system that prevents negative pressure in the cooling system.

Second factor is the rest of the parts and o-rings in the cooling system, but only during extreme load they may have a very minor leak because of the wear and rubber degradation over years of use.

If you search online, there are dozens if not hundreds topics asking this very question - "minor coolant loss, no leak found, pressure test passed"

I would advise to do this. First measure precisely the coolant loss in the middle of the service interval and right before the service. Compare the mileage, think about the outside temperature and driving style. If you consider it a major loss and it will bother you, the only way to find it is to clean thoroughly the engine bay and add coolant UV dye into the coolant. Drive aggressively 100-200 miles in warm/hot weather, after that drive with the economy mode to allow highest possible temperature and immediately inspect every part of the cooling system with UV light.

Also as a note, coolant must be replaced every 4 years or 40k miles. It has corrosion inhibitors that that have limited lifespan. FYI, BMW "lifetime" word means life of warranty.

05-21-2025

This thread sort of got resurrected, but one thing anyone can do that might be worthwhile if they notice a loss of coolant is that on the next oil change, have the oil analyzed. Any coolant in the lubrication system is problematic, but it could easily be a little leakage out of a hose connection. A cracked expansion tank is maybe the next bigger source of an issue, but there are lots of places a very small seep could lose some coolant.

I did that on some of my previous vehicles, and once, it did catch a slow leak into the oil that was fairly easily fixed before it became a much larger issue...oil can't hold much coolant before it gets too contaminated to become useful anymore and starts to cause wear problems.

06-10-2025

jad03060 wrote
This thread sort of got resurrected, but one thing anyone can do that might be worthwhile if they notice a loss of coolant is that on the next oil change, have the oil analyzed. Any coolant in the lubrication system is problematic, but it could easily be a little leakage out of a hose connection. A cracked expansion tank is maybe the next bigger source of an issue, but there are lots of places a very small seep could lose some coolant.

I did that on some of my previous vehicles, and once, it did catch a slow leak into the oil that was fairly easily fixed before it became a much larger issue...oil can't hold much coolant before it gets too contaminated to become useful anymore and starts to cause wear problems.

good advice. I've checked and toped mine off at least once since I wrote this. I also went in for routine service and asked them to check. Of course the reply was "it's in the normal range." I never wrote that letter.

06-11-2025

OP, have you pulled the plastic top off the engine and checked the turbo coolant lines? Very common area for leaks

An image attached to this post, provided by the poster

08-08-2025

JimVR4 wrote
I think there could be some misinformation here. To my knowledge the center cap is the one that provides coolant to the turbos. I believe this reservoir gets replenished by the main tank which is on the right.

I got the low coolant warning last November - it was intermittant but I bought a jug of coolant from BMW ($65 by the way), and I topped off the fluid, taking 5 plastic cups to fill (estimated at a quart). Yesterday morning I measured again (since I was taking it for service) and it was quite low once again. When I took in my 2021 M50i, they pressure checked (finding no leaks) and topped it off again. So loss of a quart last November and another quart down since then.

I was told this was considered normal but I have a hard time believing that could be true (unless the turbos are actually buring up this coolant). Still it's alarming to be sure.

My M50i is nearly three years old now with about 23K miles and I never had this coolant loss before last November. So I feel it could be a long term problem. I plan to send a letter to BMW to document my findings on what seems like an extreme loss of coolant.

Hi friends,
‘21 X7 M50i. Can anyone clarify if the main reservoir tank for the engine on the right does in fact feed into and fill the turbo coolant tank in the center? Or are they two separate lines/loops?
I had the low coolant message about six months ago and topped it off and it has been fine since. However, I just had my car serviced today and they noticed that not only does the turbo coolant tank not have a cap on it at all, the tank is entirely bone dry. I have absolutely no idea how long it has been this way and I’ve never seen anything pool up under the car or smelled any coolant. If the main tank led to that turbo tank and filled it that way, I would think I would have a low coolant message again if it flowed to the turbo tank and then leaked out somewhere, but I don’t so I am confused.

08-08-2025

The smaller coolant reservoir is strictly to cool the turbos. There is no sensor in this reservoir to notify when it's low on coolant.
The main larger engine coolant reservoir does indeed have a low level sensor.

08-08-2025

BobsM3Coupe wrote
The smaller coolant reservoir is strictly to cool the turbos. There is no sensor in this reservoir to notify when it's low on coolant.
The main larger engine coolant reservoir does indeed have a low level sensor.

Got it, that is what my shop was saying as well. Not that I can do anything about it because the turbo coolant cap doesn’t get here till Monday, but I have no idea how long I have been driving the car with no turbo coolant…literally might be for 5,000 or worst case scenario 15,000 miles ago when I bought the car in 11/24….and I push it. I guess all is fine though? Car feels strong as ever. Whats your two cents?

08-08-2025

I topped mine off in May....1st time was in Sept of the previous year
It was basically close to the MIN mark if I recall.
About 16 oz each time

Fast forward to scheduled oil change. Reported this to dealer.
Cooling System checks out fine per their diag.

I get home and my tank is over-filled. I can't even make out where the max line is as I cannot even see it. I'm going to check it out come fall....to see if whatever extra has made its way out of the cap by just driving . If not, I might siphon it back out to the max line

08-08-2025

If. you suspect there is a leak, the dealer will perform pressure test for the coolant. Normally charged around $150, to detect leaks.

08-08-2025

Yes, presuming they did a pressure test.
Even dropped it off a day earlier so the tech would have a ~cold engine~ to work off.

I know we are discussing a V8 that drinks the green kool aid.....but 32oz just doesn't disappear on its own. Note, I have never checked the tank prior to Year 2. After initially topping up 16oz to get to the max line, 9 months later, I would not expected to be topping off 16 oz

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M50i / N63B44TU3: Coolant loss / evap?