What did I undo by mistake in Cooper engine bay

[JAM35F]

In a moment of stupidity I unscrewed the cap marked in the image, then realised that the cap diagram seemed to indicate it shouldn't be opened (hand icon with a cross through it) and two pressures quoted in bar and lbs.

It was full to the brim with a green/blueish tinged liquid, some of which went on the drive and left a slightly oily mark.

What did I unscrew and is it a problem? I've done it up tight but not to a specific pressure.

[DEANO87]

It's a pressurized coolant cap. Just make sure you have screwed it back down properly and the level is ok in the bottle and it will be fine. It's there to fill the coolant system when it has been completely drained.

[JAM35F]

Thanks for the reply, It's done up as tight as I could do it, it was full to the brim literally so as the cap was replaced some came out but only a splash. Level in bottle is spot on still.

Should I try and get it put back on to a certain pressure at next service?
I assume if coolant level stays the same and car doesn't overheat I've got away with it?

[JAM35F]

Is it just a pressurised coolant cap like most other cars have? The mini being odd in having an extra non pressurised expansion tank.

If so I think there is nothing to worry about as long as it's on tight as you would do it on most other cars. The symbol showing as hand with a cross through it over worried me I think.

[DEANO87]

JAM35F said:

Should I try and get it put back on to a certain pressure at next service?
I assume if coolant level stays the same and car doesn't overheat I've got away with it?

It will pressurize itself when you next drive it and the car gets up to temperature, just put the heater on full blast and make sure it blows hot air, that will confirm the coolant is circulating properly and the system is ok.
The level on the expansion bottle may drop as the system sucks coolant in from there as/when it needs it.

[Defcon5]

JAM35F said:

The mini being odd in having an extra non pressurised expansion tank.

.

I'm fairly sure the main expansion tank is pressurised, they tend to split and spray coolant everywhere

[mrmr96]

JAM35F said:

The symbol showing as hand with a cross through it over worried me I think.

I think that's a warning not to open it unless you know what you're doing - because if you undid it whilst the engine was hot (or running) then severe injury could result from the hot pressurised coolant.

Sounds like you didn't hurt yourself, so I guess the engine was cold. In which case, you've averted the worst thing that could happen. So yeah, put the lid back on tight (hand tight, not tools) and you'll be fine.

[ging84]

the mini has no radiator cap so this is sort of in stead of it you are meant to fill it through this cap then bleed, then top up the expansion bottle, not really sure what the point is though, the S doesn't have one so you have to fill it all though the expansion bottle, but then it is difficult to bleed

[JAM35F]

the engine was very cold so no pressurised hot coolant burnt me, symbol probably is a warning about burns to hand with hindsight.

Car has been run and temp is midway on gauge, coolant level is on max line and interior fan runs hot so all all seems ok. Thanks to all for your help and advice.