Brown Coolant

[aorizun]

I'm sorry if this has been asked before, but does anybody know what this is? This is my lower coolant reservoir. It's not exactly murky, but it's brown. Last night I got a coolant low indicator and decided to check the coolant reservoirs. The smaller one was nearly full and was green like I thought it should be. The other one was low, very low actually. So I filled it up with less than a cup of distilled water and it still wasn't full. I didn't want to risk diluting the antifreeze too much as Utah weather is starting to freeze overnight. This morning, I went out to check on it and it came out brown. It was still pretty liquidy, doesn't seem like oily or anything like that.

It's a 2021 3.0 with 43k miles. Car runs fine and temps seem normal. No codes and no low indicator anymore but still low. What are my options here and what could it be? I'm already planning on getting a new cap as it's got some crustys on it and saw some people saying those go bad. Thanks for anybodys advice!

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[Thraxbert]

Are you the first owner of the vehicle?

 

[aorizun]

Are you the first owner of the vehicle?

No, I've owned it since 27k miles and since Oct. 2023. Unsure based on the carfax if the coolants ever been changed/topped up, but with me as the owner, it's never been looked at until now.

 

[Thraxbert]

No, I've owned it since 27k miles and since Oct. 2023. Unsure based on the carfax if the coolants ever been changed/topped up, but with me as the owner, it's never been looked at until now.

Ok. I asked because I had suspected there was a previous owner that inappropriately mixed coolant types. If the wrong coolant goes into the system, it can create corrosion with bad reactions to the metallurgy of the coolant loop. The corrosion makes things look dirty and brown.

My advice is to do drain/flush on that coolant with distilled water until it runs clean and clear. Then drain the system and refill with BMW-approved coolant.

You should be okay.

Edit: Out of paranoia, I would probably do another coolant change after a few hundred miles. See if the corrosion inhibitors and engine heat cycling dislodges any other crud.

 

[aorizun]

Ok. I asked because I had suspected there was a previous owner that inappropriately mixed coolant types. If the wrong coolant goes into the system, it can create corrosion with bad reactions to the metallurgy of the coolant loop. The corrosion makes things look dirty and brown.

My advice is to do drain/flush on that coolant with distilled water until it runs clean and clear. Then drain the system and refill with BMW-approved coolant.

You should be okay.

Edit: Out of paranoia, I would probably do another coolant change after a few hundred miles. See if the corrosion inhibitors and engine heat cycling dislodges any other crud.

Thank you! This will be my next move. My only question is, what’s causing it to go low? Would it be the cap or is there a common area that it leaks from that I don’t know about?

 

[PikkaGTR]

On the BMW S55, the top mount intercooler would leak and dump small amounts of coolant into the engine and cause a low coolant over time.
I suspect the intake manifold integrated cooler in the B58 is also susceptible to a similar flaw.
Other than a leaking cap or hose somewhere, there are only 3 possibilities
It was low to begin with as previous owner never topped off
You're leaking coolant out of lower hose or rad cap.
Or the engine is burning it internally

 

[Thraxbert]

Thank you! This will be my next move. My only question is, what’s causing it to go low? Would it be the cap or is there a common area that it leaks from that I don’t know about?

I admit it is difficult for me to explain the cooling loss. My best theory is that the coolant level was already juuuuust above the trigger level for the coolant level sensor. Then, a small amount of natural-and-expected loss plus loss from bonding to the surface metals pushed it over the edge to trigger a warning. I wouldn't really be worried about the coolant level until I fixed the current coolant condition, filled it back to the right level, and drove it a few hundred miles. If it happened AGAIN, then I'd be a lot more nervous about coolant leaks or damaged head gaskets.

 

[Traxion]

Thank you! This will be my next move. My only question is, what’s causing it to go low? Would it be the cap or is there a common area that it leaks from that I don’t know about?

I do regularly see white evap around my cap area so I do think the cap is a weakpoint. It's not a ton and I only got my first warning at 30k miles and then did a drain and fill. Since then I've checked it periodically and have only done a slight top up in the last 10k miles.

 

[aorizun]

I do regularly see white evap around my cap area so I do think the cap is a weakpoint. It's not a ton and I only got my first warning at 30k miles and then did a drain and fill. Since then I've checked it periodically and have only done a slight top up in the last 10k miles.

Thank you, I’ll replace it anyways to be more sure. I’m curious how much coolant flushes are costing you guys. Living at an apartment does not make it easy to maintenance this car.

 

[Traxion]

Thank you, I’ll replace it anyways to be more sure. I’m curious how much coolant flushes are costing you guys. Living at an apartment does not make it easy to maintenance this car.

I think it was about $150 at my local indy bmw shop. I did provide the coolant and distilled water for them to use.

 

[aorizun]

I think it was about $150 at my local indy bmw shop. I did provide the coolant and distilled water for them to use.

My local indy is asking for $200 and won’t use anything other than the blue BMW coolant. Would rather stay green so I’ll be looking around. Thanks for the info!

 

[Traxion]

My local indy is asking for $200 and won’t use anything other than the blue BMW coolant. Would rather stay green so I’ll be looking around. Thanks for the info!

Did you already try telling them it uses BMW HT-12 Green? It's literally the exact same as what the Z4 service manual should say.

 

[Thraxbert]

Supra manual also specifies green HT-12, so it's baffling why they'd even want to use non-OE-rec coolant.

 

[lucky phil]

Did you already try telling them it uses BMW HT-12 Green? It's literally the exact same as what the Z4 service manual should say.

That would mean that they 1 would need to use something "different" to what they usually use ( read scary for them) and 2 they would need to source the green coolant at a cost much higher than they buy the blue coolant in bulk therefore cutting into/eliminating their profit margin on the materials. Same with owner supplied coolant, no mark up for them in that.
Phil

 

[Bananamkv]

Ok. I asked because I had suspected there was a previous owner that inappropriately mixed coolant types. If the wrong coolant goes into the system, it can create corrosion with bad reactions to the metallurgy of the coolant loop. The corrosion makes things look dirty and brown.

My advice is to do drain/flush on that coolant with distilled water until it runs clean and clear. Then drain the system and refill with BMW-approved coolant.

You should be okay.

Edit: Out of paranoia, I would probably do another coolant change after a few hundred miles. See if the corrosion inhibitors and engine heat cycling dislodges any other crud.

is this a drain/flush from radiator lower hose and fill at cap? My coolant is brownish too and was looking to just a full cleanout and refill to try and see if it is still getting contaminated or if they mixed coolants at some point.

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