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Just looking for a second opinion (or 10 ;) ) before I start diving into this.

Mini R50 - Old coolant was the red/pink stuff and was showing bits of crap in it. Flushed with Holts Speed Flush, and filled with 50/50 DI water and Comma G48. Spent hours bleeding the system and all seemed fine.

Now a week or two later I've noticed the expansion tank keeps dropping to the low fill mark, top it up to max, keeps dropping to min again after driving.

Went to take a closer look this morning and the top of the expansion tank lid has began to melt and there are white stains on the hood liner, I'm 95% sure the car hasn't overheated during this time because I've kept an eye on it.

Looking for some opinions? Don't want to influence anybody so I'll keep my guesses to myself for now? Thanks (y)
 

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If your still having issues replace the pressure cap, one on mine looked fine but letting the engine sit and get up to 100 degrees it would boil over before getting to the radiator fan switch on temperature of 105 degrees, only about £15 for a new cap nice easy fix!
 

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If your still having issues replace the pressure cap, one on mine looked fine but letting the engine sit and get up to 100 degrees it would boil over before getting to the radiator fan switch on temperature of 105 degrees, only about £15 for a new cap nice easy fix!
Sorry to hi Jack this thread but I have a 2005 mini where the coolant will escape from the top of the thermostat housing cap, I replaced the entire thermostat and housing but the problem stayed, is this what happened to your Ollie? I have heard that unless you use the bwm thermostat housing you can have all sorts of problems, I did get it from euro car parts so assumed it would be OK? Where did you get the cap from?

Thanks

Rob
 

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Not sure on the 05 model, is that still the tritec? Mines an 03 had the expansion tank filling up as the engine got hotter then as the engine got just over 101 degrees (checked via the obd) the tank started to boil, got a Febi (oem) cap off eBay for around £13 works a charm, just need to fix the radiator fan now! I didn’t have any leaks out of the thermostat housing cap (the bit I changed) it just wasn’t holding pressure and letting it back to the expansion tank, might now also have a small weep on the top of the thermostat housing where it mounts to the engine though 🤦‍♂️
 

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Got to post in two parts there will be an image in a second, did you replace the cap highlighted in yellow? Mine is passing water at pressure at the top of the thermostat housing circled in red
 

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No I replaced the cap circled in red, it wasn’t leaking out the top of it just past the seal inside causing the expansion tank to fill
 

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No I replaced the cap circled in red, it wasn’t leaking out the top of it just past the seal inside causing the expansion tank to fill
OK mine hasn't done that but i guess if both seals aren't doing there job I mine wouldn't fill the water bottle but just come straight out the side, think I have found the part on ebay might order it, was just about to send it to the garage I have done a compression test and the head is good so I was starting to be at a loss for ideas
 

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Interesting that you get nothing building up in the expansion tank? Possibly a blocked line to the expansion tank? Should be an easy check, otherwise I’m not sure how it would leak past both seals on the cap without filling the tank
 

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Interesting that you get nothing building up in the expansion tank? Possibly a blocked line to the expansion tank? Should be an easy check, otherwise I’m not sure how it would leak past both seals on the cap without filling the tank
Had the pipe off and it wasn't blocked, if both seals have failed I am assuming it takes the path of least resistance the housing gasket and stat itself was only £25 and I imagine £13 of that isn't spent on the cap alone, so might just buy the cap on ebay and give that a go
 

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Just had the new cap turn up and it does feel a lot better build quality, took it out for a spin and the coolant went from max to min but I expected that as it was pretty much ran out of coolant, i had topped it up before the run and bleed it, the only thing I noticed was there was some gases maybe steam escaping from the top of the thermostat housing, is that expected with these engines?
 

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As the engine cools down after a run it will pull coolant back in, I tend to top the coolant up the next morning so then I know when its stone cold thats what I should expect, sounds like your system may have had air in it that got pushed out when it was run, when you say gases/steam escaping is this with the cap removed or is it escaping from the joint of the thermostat housing to the engine block?
 

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It looked to be coming from underneath the cap but I didn't take it off as it will still under pressure, took it for a long run tonight stopped half way and it hadn't taken any coolant from the bottle, it was just above the min when I set off, when I got home it had taken a little out of the bottle so it was just below min, but I could hear running water, couldn't see a leak at all, but the noise was just like when you run a tap and only lasted for a second or 2 so to me I don't think that's a problem, if I check the bottle again in the morning do you think it might have put some of the fluid back in it? Thanks for all your help with this.
 

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Hmm thats interesting, steam would still indicate there was a leak around the cap, is the top of the thermostat housing where the seal touches nice and clean/smooth? I would expect if it had warmed up to have expanded into the tank a bit (straight after driving) if it has gone down while driving I don't know what to say as unless the coolant had cooled really quick while driving causing it to draw more in to the system I don't know how it would have gone down other than a leak, although some movement is probably fine, have you used the heater at all? that might have displaced some air if it was used which would have then left the system at the cap hopefully, I would expect the level to move around a little after bleeding until it finds it's happy place, I would top the coolant up to max when cold and monitor it over a few runs to see what is happening, no problem, happy to help as i'm sure there will be something I don't know how to do that hopefully someone will help me with!
 

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So good news I think, I can't see any new coolant sitting on top of the gearbox and the level in the bottle is going down so its been for two short runs today started at max and just went below min, so I have topped it up again to max but noticed a cut out in the top of the expansion tank, is this normal? Tried googling to see other pics but couldn't find any good quality images of the push on cap like mine.

278381
 

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The coolant is still going down? or it was just low to begin with? that slit in the top I would expect to just be an air breather to allow for slight expansion in the tank under normal conditions, saves stressing the rubber cap!
 

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Yes its still going down but not at the rate it was and it could just be I didn't fill it up enough, I am hoping anyway, its going for another run tomorrow so will see what happens after that
 

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So its been for a much longer run today and the bottle is back down to pretty much the same level after a shorter run out yesterday, I am wondering if the bottle has a crack then when it gets up to pressure its leaking, there is still no sign of a leak at the thermostat or on top of the gearbox where it likes to puddle, I will do some more digging before the f1 on Sunday see what I can find
 

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So now I am at a loss and wondering if this car just doesn't want to be saved, hopefully there will be two videos attached, just took it for a quick spin water on max before I left when I got back with the engine still running it was below min and smoking out of the top of the thermostat, when I turned it off it made a strange noise and pushed water back into the bottle so it was between min and max now, do you have any more ideas or should I just throw in the towel and send it to the BMW garage that gets good reviews on Google in Derby

Had to upload vids somewhere else so hopefully external links are allowed

noise when engine turned off

Steam escaping
 
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