Baby BMW Forum banner
1 - 6 of 6 Posts

·
Registered
Joined
·
107 Posts
Discussion Starter · #1 · (Edited)
I thought I would post this as a guide to how to fix the issue with coolant "consumption" on the B58. Please note - this is not an official recommendation but is merely how I perceive the issue and how I chose to fix it on my car.
Conventional coolant bottles ordinarily incorporate a standard cap design where the screw cap is simply tightened down against a sealing washer in the lid of the cap, much like any container with a screw cap lid. For some reason best known to BMW, they chose to redesign the wheel and produce the seal by virtue of a series of O-rings which are an interference fit with the neck of the reservoir tanks. This means that neither cap needs to be tightened down to produce the seal - the lid for the main tank merely clicks into its final postion. The intercooler tank lid does come to a hard stop but there is no point tightening it down hard because this isn't what makes the seal - in the case of this tank, it is made by a single O-ring housed in the cap and which fits on the inside neck of the bottle - the main cap has three O-rings, two smaller and one larger.
The problem is caused by the O-rings drying out and resulting in significant friction between the contact faces of the O-ring seals, the cap and the filler neck. This can be so significant as to ruck up the O-rings, tear, score and damage them. This is made worse by the presence of powdery limescale deposits which will reduce further the quality of the seal and add to the damage to the O-rings. This can happen to such an extent that the caps can actually be difficult to remove from the reservoir tanks.
Thus . . the solution is to remove the caps, remove the O-rings and then scrupulously clean all deposits from around the inside neck of both tanks and whilst not so important for producing a seal, I also cleaned up the threads on the caps and the bottles. A soft cloth soaked in vinegar will help remove the limescale deposits or indeed a little Harpic Power Plus Max lavatory cleaner which is quite acidic and will make short work of the deposits. Use it to dampen a cloth only as it is corrosive and so wipe away fully after cleaning.
The main problem you will face is how to remove the O-rings. You need something pointy to get underneath them and lever them off - such as a co"cktail stick but . . . I found a co"cktail stick wasn't really strong enough. DO NOT USE A BLADE . . .it would be very tempting to stick the point of a knife or a stanley blade under the O-ring to lever it off but if you do, you will almost certainly cut into it and your seals will be worse than if you hadn't ever bothered - be warned. I used a dental probe - pointy but not sharp. A very small flat bladed screw driver with a "rounded" smooth tip might work or better still, a lollipop stick cut to a "chisel point" but slimmed down to maybe 3-4mm wide - this would enable you to get under the O-rings and tease them out but without cutting into them. Don't forget . . . it is equally important NOT to scratch the plastic face of the cap, against which the O-rings seal and this is the main reason NOT to use anything metal if at all possible - lollipop stick is likely to be the best option.
Once removed, scrupulously clean their recesses of any limescale and the O-rings themselves before again, wiping down with fresh water and getting rid of any acid if using vinegar or lavatory cleaner.
now lube the O-ring recesses with Silicone grease and the O-rings themselves. The idea is to leave nothing more than a shiny surface and so wipe off any residue or excess - you're not interested in leaving dollops of grease hanging off the things . . . just a shiny surface - nothing more. You can always repeat this exercise, indeed - I have done it about 3 times in 6 years!! No need to put grease on any of the threads; just make sure they're clean so they don't grate and grind.
Mineral grease WILL, WILL, WILL damage the O-rings. By mineral grease I mean pretty much any grease out there be it chassis grease, bearing grease, brake grease, lithium grease etc etc etc. You absolutely must use Silicone grease. If it doesn't say silicone on the tube then it isn't silicone - don't risk it. I used Dow Corning Molykote. One other alternative is red rubber grease which is not mineral based, can be used in the same way but I would suspect wouln't be quite so water resistant as silicone - see pictures.
I have made a very short video of how easily your caps should come off and be replaced - those of you losing coolant will immediately recognise the difference between mine and yours - easy fix if you're interested.
Photos and video links below . . . .


(1) IMG 7268 - YouTube






Automotive tire Hood Finger Rim Automotive design
Wheel Automotive tire Automotive lighting Motor vehicle Tire
Hand Camera accessory Camera lens Cameras & optics Finger
Font Material property Electric blue Tints and shades Fashion accessory
 

·
Registered
Joined
·
285 Posts
Thank you Javaman. I do personally think that BMW are more than aware of this,as to why they have not made their customers and maybe service agents aware would be pure speculation and I’m not going there!
Once again Javaman well done for your insight and explanation of the issue.
I recon this will be on the FAQ list on all bmw b58 forums within a year.
 

·
Registered
Joined
·
261 Posts
Laughing at that video. I checked mine before a recent trip and for the big cap I had 2 hands gripped onto it as tight as I could and wrestling it round about 1cm at a time.

Thanks for putting this together. Hopefully mine will be like in the video soon.
 

·
Registered
Joined
·
107 Posts
Discussion Starter · #4 ·
Laughing at that video. I checked mine before a recent trip and for the big cap I had 2 hands gripped onto it as tight as I could and wrestling it round about 1cm at a time.

Thanks for putting this together. Hopefully mine will be like in the video soon.
Fear not . . . mine was exactly the same. It was so hard to get undone, I thought I must be doing something wrong and went and checked the manual to find out how to take the cap off!!!! It literally got tighter and tighter the more I turned it. I got away with it though and kept the same O-rings.
 

·
Registered
M140i
Joined
·
114 Posts
Laughing at that video. I checked mine before a recent trip and for the big cap I had 2 hands gripped onto it as tight as I could and wrestling it round about 1cm at a time.

Thanks for putting this together. Hopefully mine will be like in the video soon.
Mine is like this as well. Need to get around to sorting it out this week. Just ordered some supplied off Amazon.
 

·
Registered
Joined
·
816 Posts
I've never had a limescale issue but years ago a thin smear of silicone grease on the o rings solved my steady coolant loss.
I found a thin smear on the plastic thread made a world of difference and removed any tightness.
 
1 - 6 of 6 Posts
Top