Mystery coolant residue!? 2.8i Single VANOS

Kaz117

Kaz117

Regular Member
British Zeds
Joined
Oct 18, 2025
Points
23
Location
South Lanarkshire, Scotland
Model of Z
Z3 Roadster 2.8i
Hi,

M52B28 Pre TU (single VANOS)

There seems to be this odd coppery-like residue baked on to mostly the coolant exp tank cap, and a little bit of it in the expansion tank where there's no coolant touching but just air.

Is this anything to worry about? Coolant is in excellent condition and the temp keeps exceptionally well even with the aux fan not working.

Thanks.

IMG_6603.webp
 
Are you using G48 antifreeze/coolant mixed with distilled/ deionised water (or ready mixed G48)?

I know that the aluminium blocks don't like tap water or non G48 (aluminium block special, bmw approved) antifreeze/coolant but I am not sure if it would cause that
 
Smudgemanuk said:
Are you using G48 antifreeze/coolant mixed with distilled/ deionised water (or ready mixed G48)?

I know that the aluminium blocks don't like tap water or non G48 (aluminium block special, bmw approved) antifreeze/coolant but I am not sure if it would cause that
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Haha that's the fun part, I have no idea what the previous owner put in there. The cooling system was refreshed well, works excellent, but have no idea what is actually in it.
 
Is the residue slimy, or 'metally'. IE, is it dried liquid, or dried solids (metal)?

It could just be residue from previous coolant, which was either not suitable and reacted with something, had just broken down due to age, or the remnants of gunge from the previous coolant.

I would clean the residue off the cap and see if it comes back, and if so, how quickly.
 
Pond said:
Is the residue slimy, or 'metally'. IE, is it dried liquid, or dried solids (metal)?

It could just be residue from previous coolant, which was either not suitable and reacted with something, had just broken down due to age, or the remnants of gunge from the previous coolant.

I would clean the residue off the cap and see if it comes back, and if so, how quickly.
Click to expand...
its not sludge at all, just dried onto the cap. none in the coolant mixture at all. its hard to wipe off.
 
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