Description Reviews MINI Cooper S Aluminum Expansion Tank! We all know that the expansion tank is the weak point in the MINI cooper S's Cooling system. Buy this aluminum tank and never have it fail again! It uses the OEM cap so you know that it will pressurize correctly! All needed hardware is included for a quick install. You will need to top off the coolant so it might be a good idea to do a flush at the same time. Also this unit doesn't come with expansion tank cap, so you might want to replace that at the same time to make sure everything in that area is working correctly. 1 Review 5 A High Quality Improvement Over the Stock Plastic Reservoir Posted by Stuart Rothstein on 18th Jun 2018 Ordered online, shipped, and received extremely fast. This aluminum reservoir is very impressive with a high quality fit and finish, and cost little more than the stock plastic unit. My only complaint is that the allen head screws (as supplied with washers) can be a bit of a pain to get screwed in all the way, I think hex heads might be easier. Just make sure to run the screws in and out a few times before trying to install the unit, so you can just use your fingers. So far, Detroit Tuned has delivered high quality products at a fair price.