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Discussion Starter · #1 ·
Been meaning to check for ages, finally did it today, its well below minimum, you can just about see a bit of fluid in the expansion tank, ive not had a warning yet and im going to top it up this afternoon.

Had zero issues with coolant loss so far in owning the car (2 years) last time i checked was a few months back, dont know if the lid was properly secure after the last service but im hoping its as simple as that, whats the chance its something more major? And is there any chance i could have done any damage so far?

Cheers
 

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Discussion Starter · #2 ·
Used about 750ml/800ml when i topped it up to get it just above max by a smidge.
 

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did you top it up cold ?
 

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i'd have topped it it to just above min to allow for expansion
 
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Its only a guess but as the engine runs at 109-110C my guess is some coolant makes its way past the
O rings. Mine was slightly low at 13K miles and the cap was a pig to remove. There was a small amount of white crystal deposits under the cap. After topping it up I put a smear of silicon grease on the O rings and a small amount on the threads. I would think judging by previous reports that the car will cut the power in the event of the coolant getting too low and it should trigger a dashboard warning.
 

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Discussion Starter · #9 ·
Do you mean the main tank or the small tank? I have topped up the small tank once or twice but cannot remember topping up the main tank in 5 years.
Main tank buddy for the engine, cooler tank has always been fine.

Poster above i wonder if it is the cap has degraded maybe, what do you mean about the o ring which bit is that?
 

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Same issue here, lost coolant, topped up, was still losing a bit of coolant. Replaced the cap and haven't had to touch since
 
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Checked mine a few days ago ahead of a long-ish drive and noticed the main tank was at or just below minimum. Nothing seen on the iDrive to indicate a low level. Check radiators and no signs of a leak. Topped up and checked periodically over the next few days and coolant level seems to be stable just below the max marker. Mine also has the powdery white residue around the base of main tank filler cap so might need to look at changing the cap soon.
 

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Back in 2018, after about a year of ownership from new, my 140 drank about a litre of coolant. I topped it up and it has never used so much since, yes I top up maybe once a year, had a service in March and the buggers hadn't topped it up; it only took a few ml to get it to the indicator.
 

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Discussion Starter · #14 ·
Lost a small bit of coolant again with the new cap, not loads just a small amount, strange, cars running absolutely fine and no other symptoms at all dont have a clue where it could be leaking.
 

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2016 M240i
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I just think they use a bit of coolant every now and then, maybe the hot engine temps etc.

I had a new cap back in 2016 and it's never really lost much coolant since then, just a bit every 6 months. However, having been away in Spain for the past 2 weeks, and the car effectively not moving for 3-4 weeks I decided to check fluids, charge battery etc before using it again.

Both coolant tanks were above Min, but only just so I topped them both up. That's the first top up since 2016 and it could be because the car has been sat for 3 weeks, or even the recent high temps. I'll just keep an eye on mine going forward, but I don't think its anything to worry too much about at this stage.
 

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The B58 doesn’t “use” coolant - it gets past the crappy tank cap. Mainly the main coolant tank but the intercooler tank as well.
Absolutely no point changing the cap unless you’ve fubarred the O-rings.
Remove the cap and tease the O-rings off. There are three on the main cap. Use a strong cocktail stick or similar (I used a dental probe) but not anything that will cut or damage the O-ring or you’ll be worse off than before you started.
Now wash every single piece of scale deposit from the O-rings and their grooves in the cap. Even the smallest amount of scale will result in a leak.
Likewise, make sure the inside of the filler neck of the tank is scrupulously clean. Now wipe the thinnest smear of “silicone grease on the O-rings, their seats in the caps and on the inside face of the filler neck. Wipe off any remnants to leave a shiny surface and nothing more.
Both caps will now effortlessly glide on and off and your car won’t “use” coolant. You might need to repeat this process annually. 👍
Be warned - silicone grease is silicone grease and not any old axle, bearing it chassis grease you happen to have lying around. Use any of these and you will end up in a pickle as your O-rings will swell up like they’re on Viagra - umyiu’ve been warned! 🙄
 

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2016 M240i
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The B58 doesn’t “use” coolant - it gets past the crappy tank cap. Mainly the main coolant tank but the intercooler tank as well.
Absolutely no point changing the cap unless you’ve fubarred the O-rings.
Remove the cap and tease the O-rings off. There are three on the main cap. Use a strong ****tail stick or similar (I used a dental probe) but not anything that will cut or damage the O-ring or you’ll be worse off than before you started.
Now wash every single piece of scale deposit from the O-rings and their grooves in the cap. Even the smallest amount of scale will result in a leak.
Likewise, make sure the inside of the filler neck of the tank is scrupulously clean. Now wipe the thinnest smear of “silicone grease on the O-rings, their seats in the caps and on the inside face of the filler neck. Wipe off any remnants to leave a shiny surface and nothing more.
Both caps will now effortlessly glide on and off and your car won’t “use” coolant. You might need to repeat this process annually. 👍
Be warned - silicone grease is silicone grease and not any old axle, bearing it chassis grease you happen to have lying around. Use any of these and you will end up in a pickle as your O-rings will swell up like they’re on Viagra - umyiu’ve been warned! 🙄
I did that with my new cap back in 2016/17 ish and it’s still clean to this day. It works great but the caps now always feel like they’re not tight enough. :D

Maybe mine hasn’t used any, it was still above min. Maybe it just settled somewhat while I was away.
 

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I did that with my new cap back in 2016/17 ish and it’s still clean to this day. It works great but the caps now always feel like they’re not tight enough. :D
yes - exactly. The seal is made between the O-rings and the filler neck and NOT by tightening the cap down as per a traditional cap and sealing washer.
When the O-rings are dry and have a little scale mixed in for good measure, the caps can be so tight as almost impossible to remove!!!!
Both mine almost spin freely and are as loose as Katie Price’s knicker elastic !! 👍
 

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Discussion Starter · #19 ·
When people say grease the o ring are you reffering to the plastic threads on the coolant tank? I.e. can i just rub the grease on the plastic threads then screw the new cap on?
 
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