· Drove home slightly different route (via motorway)
· Stuck in traffic but not much more than usual
· Car suddenly started steaming from under bonnet with violent bubbling sounds
· Car temp gauge was still reading normal (middle)
· Opened bonnet & saw coolant coming from Expansion tank cap
· Let it cool down & opened cap – level was below minimum
· Filled up with only water (no antifreeze available at time)
· Drove home perfectly well
· Re-checked coolant level / topped up with water only again
· Checked for leaks – all ok as far as I could tell (in low light)
· I haven’t bled the system yet
· Researched way to check real-time engine temp via OBD menu
· Ensured rad cap was super tight
· Set display to show live engine temp
· Drove normal route (mixed town / b-roads)
· Again, drove perfectly – no noises, misfires or smells
· Was getting heat from heaters fine
· Average speed was 45mph – temp stayed between 83-86
· Got to work – let car idle for 5-6 mins – temp rose to 91-92
· Car temp gauge still showing normal (middle)
· Turned on aircon to see if fan operated & if temp reduced
· Fan didn’t operate / temp stayed the same (should i have left the aircon on longer?)
· Shut off engine & checked rad cap for leaks – all ok
· After a few moments, a slow trickle appeared from the rad cap
Today, I noticed that the engine temp would rise (86-88) when I increased the engine speed but would reduce again(83-85) when I slowed down or at traffic lights etc even though no/reduced airflow through radiator? – is this normal?
On boxing day, the car suddenly lost all its coolant while driving & had to be recovered. Green Flag confirmed that a hose pipe by the thermostat housing hadn’t been secured properly & blew off resulting in the leak. That was secured properly & the car has been fi>
On boxing day, the car suddenly lost all its coolant while driving & had to be recovered. Green Flag confirmed that a hose pipe by the thermostat housing hadn’t been secured properly & blew off resulting in the leak. That was secured properly & the car has been fine since – I bled the cooling system myself at the time once re-filled with 50/50 coolant.
I only bought the car in May & have kept an eye on the coolant as have had to top it up probably every 6 wks or so. I replaced the expansion tank cap in August as the original one looked poor. Also, According to the service book – the car has had a new water pump at approx 76000 miles – literally just before I bought it. From what i can tell having read up – the first stage fan doesn’t seem to work but the second stage definitely does as it came on often during the summer in traffic as well as last night when it broke down.
Getting a coolant pressure test done today but does anyone have any input please?
Hope that helps & isn’t insulting anyone’s intelligence haha
Hi Hollywood, the coolant pressure test is a good idea, as if you have a weeping head gasket (or some other internal leak), the pressure test should pick that up.
Took a look in my Bentleys manual, here is what it said about the electric cooling fan:
"The cooling fan operates on low speed when the A/C is switched on and the A/C system pressure reaches 8 bar. The fan switches to high speed should the A/C system rise above 18 bar. For the engine cooling system, the fan operates on low speed at 105 degrees C (221 degrees F). When the temperature drops to 101degrees C (214 degrees F) the fan will switch off. The fan switches to high speed at 112 degrees C (234 degrees F) and remains on high until the system coolant temperature drops by 4 degrees C (7 degrees F) at which the system reverts to low speed."
Hope this helps explain a bit about how your fan "should" operate according to the manual I've got here.
I know you say you've bled the air out of the system, but would it be worth checking for air again in case there's a bit more still trapped inside?
Thank you JJ - much appreciated. Got the car back this evening. The garage did a pressure test and reported all was well but the only thing they couldn't check was the rad cap itself so they assume it's that not sealing properly?
Again, I went into the OBD menu and got it to show the coolant temp while driving home. I gotta say, it stayed pretty stable to be honest - average speed was 35mph with a little stop/start and the temp range was between 84-88 while cruising and rose to a maximum of 92 in stop/start traffic in town. There was a smell of coolant when standing at lights so clearly something was escaping somewhere?
Got home and checked it out, re-tightened the rad cap as there was evidence of leakage.
However - there is now also seeping from the tank seam. This wasn't there before today so could the pressure test have now also caused the tank to split a bit?
Gonna change the tank/cap now anyway - should I just buy the BMW tank (assuming the design has improved) or is there a better alternative? Don't want to spend more than I already have on this motor tbh...
I had the exact same problem and symptoms a few months back. It turned out that the cool ant cap hadn't been tightened fully which lead to the cool an escaping. I first noticed when the engine fan came on when the car was switched off.
I have a feeling it was Mini as it had gone for a service only 3 days before the problem occurred.
Cheers for the advice! Just drive it to work via the motorway as normal route flooded. Properly ******** myself expecting it to boil over again. It didn't! Drove like a champ...
Could only travel at around 50mph for most of it at the temp more or less was 84-86 occasionally rising to 88 when going uphill.
I have no idea what the normal running temp range should be when warmed up so is the above figures ok or should i be worried? Also, how can i tell if the thermostat is working as it should be? I assume the temp should get to a certain point and then cool by a good few degrees?
Back again. Drove home just now - all was going well until I hit traffic at which point temp went from a stable 86c up to 90c quickly and I started seeing steam from the bonnet. The temp was showing at 98c when I managed to pull over and switch it off. Popped bonnet, coolant streaming from the rad cap.
Didn't loose too much coolant - if anything when I took off the rad cap a load more just poured out and the level was MUCH higher then the 'max' mark????
I'm now thinking the expansion tank itself isn't knackered at the seam as perviously thought - it was just the coolant running from the cap into the seam making it look like a leak was there?
After all, the pressure test done yesterday would've shown the tank leak if it was dodgy right?
Going to BMW in the morning to pick up yet another rad cap to see how it goes... I'm guessing the seal on the cap is shot so possibly not being able to handle the pressure at 90c plus?
- just out of curiosity - does anyone else have to really really tighten their caps? Mine has to be done so tight I have to use one of those rubber strap things to tighten/loosen!!!
I'm worried that even when I get the stage one fan fixed, it'll still overheat before the low speed fan would've kicked in.
The R53 coolant tank was known for leaking around the seam and were later improved in quality......if the seam or the pressure cap leak under pressure the temperature will rise and therefore coolant boils. This is because the boiling point of a liquid is raised when held under pressure.....thats why the cooling system is pressurised.....if the pressure leaks away then the boiling point drops. When you release the pressure cap there should be a 'hiss' as pressure is released....however don't release the cap when hot or at least take precautions against steam/hot coolant spraying out.
"The radiator/expansion tank cap actually increases the boiling point of your coolant by about 45 F (25 C). How does this simple cap do this? The same way a pressure cooker increases the boiling temperature of water. The cap is actually a pressure release valve, and on cars it is usually set to 15 psi. The boiling point of water increases when the water is placed under pressure." HowStuffWorks "How Car Cooling Systems Work"
The engine temperature seems about right.....modern car temperature gauges like the Mini's are 'dumbed down' to show 'normal' over a wide temperature range in order to not worry the driver unless things get extreme.
people are saying when the car starts overheating that I should turn on the aircon as the fan will activate. I reckon my air con fan ain't working. The fan doesn't seem to come on at all. When I press the button, I can hear what sounds like the compressor going and the car it does blow out much colder air but even after a good 10 mins no fan.
All I managed to do in order to get back home was crank up the heating to 'HI' on full blast - that seemed to keep the temp at about 88c (even in mild stop start traffic)
Is there an easy way for me to check it out step by step?
Right, I picked up the new cap from BMW just now. This is now the second rad cap since I bought the car in May as the first one's seal looked well roped. Got a right result, turns out the parts manager is an old mate so got it free haha...noticed the old cap has a chip on it (see pics)
Could this simple chip cause the boil over?
As I say, the car drives a dream and the pressure test done confirmed everything else checks out - the cap was the only thing they could check. Coincidence?
Slightly concerned at what could've caused the chip, though!
Really hope this sorts out the leak so can then focus on the stage one fan fix...
As long as you have coolant in the heater it adds to engine cooling when on full with the blower fan as you are taking more heat out the system.
In old classic Mini's this was always a way of getting excess engine temperature down in traffic even on a summers day...as your passengers roasted!
However if your heater ever goes cold while set on hot stop driving as it means there is no coolant in the heater matrix so there is a leak!
The cap's pressure release valve may be chipped and faulty/broken from new and therefore not maintaining pressurised system....this would cause overheating and as a bonus be a cheap and easy fix.......fingers crossed!
Quotes from the NAM thread:
"The cooling fan first stage speed is like a base point to provide a constant regulation of temperature while 2nd stage fan is for peak temperatures reached when car is stationery or under load, it quickly brings the temperature back to the regulation zone.
At 105C the low speed should be on
At 112C the low and high speed should be on together
OR if the refrigerant pressure from the A/C compressor is good and Air Con is on then the fan should also be on."
"In a perfect Mini cooling system, the low-speed fan will come on (and stay on) when you turn on the A/Con - always. If the fan does not come on (low-speed) when you turn on the A/C, but then comes on at high-speed after a few minutes (you'll know it's on high - very loud), those are the symptoms of a burned-out resistor."
"I decided to spend some time observing the fan in my garage and after a while of having the car on and the fan still, I decided to turn on the A/C and the fan did turn on. I turned the A/C off and the fan remained on. Waited some time and it stayed on at the same speed. So I got back in the car, turned the A/C back on and rev'd it for a while and then... high speed came in.
So in short, I was able to determine that my fan does indeed work at low speed and high speed."
Ok! Put the new rad cap on - been driving it since Saturday in various conditions. Deliberately drove the identical route i broke down on last week to replicate similar temperatures etc. glad to report that it didn't boil over. According to OBD temp gauge, the heat rose to a peak of 105c in traffic before i managed to start moving and it then steadily dropped back to 86c all the way home. Thought i better check the tank for leaks - none!
However, after about 20 seconds, i could hear a very faint whistling/hissing sound coming from the tank area.
I definitely bled the system properly over the last three days so it cant be trapped air - what you guys reckon?
Hi, do you mean you could hear the sound after the car was swiched off ?
The pressure cap will let out pressure when its over 16psi (I think its 16) so as your car cools down it needs to draw the air back in which it pushed out. It will be a very faint hissing sound, the cap is designed in a way that it holds the pressure in the system but draws the air back in easily like a kind of valve. I hope I explained that clear enough. My R53 does this
Thanks, mate! I was thinking along those lines myself but was paranoid. Yeah, it was a really faint whistling noise after id turned off the engine.
There was definitely no evidence of a leak and also, when in was previously leaking i'd be able to smell the coolant which i couldn't last night (thats what made me think it was the cap sucking air back into the tank)
I have the alloy coolant tank with standard cap & if I go for a good blast round the next time I open my bonnet I have pink coolant marks down my nicely polished tank because as it blows the pressure out it obviously contains steam & that does my head in, even though it does this I have only had to top the tank up twice in 7000 miles & that was only around 100ml each time. I have been looking around at the different tanks with normal radiator caps & an overflow pipe as I have a thing (ocd ?) About a nice shiny engine
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