I had a problem with the coolant light going on for few minutes after running the car from a cold engine and then it would turn off by itself. I took it to the mechanic and they added coolant and, while in there, I also put some premium gas from a pump that I have been so far using its 'plus' grade. Then aftewards I noticed that the engine struggles and makes a muffled noise when accelerating. The noise is more apparent when on low speeds specially on uphills; you can feel that there is an strain on the engine. Also since then the engine heat up very fast, but the coolant light hasn't come up again. The mechanic says there is probably something wrong between the engine and the exhaust but they don't know what it is and they suggested I take it to a BMW service center but that is not an option for me since there is non nearby and I can't take the car on the road in this condition for long distances.
I would really appreciate any suggestions that you might have.