2006 mini S 65,000 miles purchased used recently. After 1 week of driving 30 miles daily the coolant tank leaked and blowing steam. Car runs cool never hot and with no smoke. Thoughts?? Coolant tank plastic and brand new.

Did you replace the coolant cap too? If not, I’d be suspicious of its ability to hold pressure.

I too replaced my functional yet aging oem plastic tank (as a time item) with a metal one. They now can be found on ebay for around $50 +or -. Wouldn't hurt to buy a spare oem cap. They cost about $10--cheap insurance. I always keep a spare in the boot. Found out that if you keep the coolant level just above the center stand pipe, you won't have any problems. It's an easy DIY ( info online) but as Fly'n Brick mentioned it takes small hands to secure the tank to the support bracket. Good luck.

thanks for all the info. I am definitely going to upgrade to aluminum. I have been reading a lot about it. The sad truth is I noted the temp gauge began to climb today while sitting idle after driving about 10 minutes and the fan was on and it continued to climb quickly. I shut the car off before it got too hot. Small amount coolant leaking from coolant tank. I am not going to lie by this makes me very skeptical of head gasket. Love the car. It’s got soul but hopeful it’s not a huge expensive fix.

Where is the coolant leaking from?

The cap?
​​​​​​​The center seam of tank?
Hose connections?

Zsm asked if you replaced the coolant tank CAP as well. Did you? Bad caps are a very common failure point, no matter if your tank is plastic or metal. If they can’t hold the pressure, you will overheat.