I just got my clutch replaced in my 2007 mini cooper and now it gets about 90 miles less per tank every time I drive it. I took it back to the garage and they said there's nothing wrong with it. Why is my car performing worse with a new clutch?

That is a good question. The clutch should have no correlation to you fuel consumption, provided you are driving it in the same manner as before. However, your master cylinder is used by both your clutch and braking system. If the shop did not get the air bubbles out of the system with the proper tool, perhaps your brakes are hanging up/not-fully releasing. I would ask the question. Is the shop experienced in Mini repairs?

Michael is correct a clutch should not effect your fuel economy. The brake hang up may be your best issue to check for. An experienced mini technician doesn't have to remove the clutch slave causing air into the brake system. Also make sure you also watch your driving habits with the new clutch those have the biggest affect on fuel economy.

I'll definitely ask my guy about it. The clutch is also acting weird because it lost it's sensitivity after a month and there is no longer a 'sweet spot' in the clutch and I can push it in anywhere and the car will shift. And it won't fully shift into second sometimes or it'll pop out and make a grinding noise. Basically, it's acting the way it was before I got the clutch replaced. Would this be symptoms of the brake hang up you two mentioned?

No what you are saying has nothing to do with brake hang up. What your describing is either a transmission issue or a shift cable problem. I would talk to your guy about these issues your having. Why did you replace your clutch? Was this happening before replacment?

Oh goodness. I replaced my clutch because the car was giving me a lot of those problems and my guy said that replacing the clutch would help/fix those problems (the popping out/grinding noise/no-longer-sensitive clutch). Transmission or shift cable? Hm, okay. Also thank you for all of your answers. This has been really helpful so far.

Those diagnosis are just off what your saying and what I have seen of course its not a proper one. You should have it checked out by a Mini shop to make sure your not having issues with the transmission. Also what type of clutch did you replace it with OEM or aftermarket? Glad I could be of any help to you if you have an more question feel free to message me.