I'm having the coolant being forced out of the expansion tank by popping the cap and sometimes just coming out with the cap still on. I have been topping up with coolant and water but unsure of the mixture %. Is the 50-50 mix essential and as I'm not using it is this causing my problem?
I've looked at the articles and tried checking those I'm able to rule them out. I noticed that another reason for this is the fan not kicking in. Mine kicks in but I'm not sure of it's a stage one fan or stage 2. I used the diagnostic test to check the temp and when the fan kicks in and it comes on at 117'C. I think this maybe stage 2 as I assume it should kick in earlier to stop overheating. So at what temp should stage one kick in?
My car is a 02 Cooper.

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This post was auto-generated based upon a question asked on our tech article page here:

The fan turns on at 105°c and high speed kicks in at 115°c.

Coolant mixture will not cause this issue.

- Nick