Coolant level after new sensor and MPG

[JetMech]

Hey guys, sorry if this is redundant but I couldn't find anything to encompass everything. I recently got a new radiator and put in a new coolant level sensor because my level indicator light was coming on at start up. It goes away when I start driving. Anyway, the new sensor didn't work and it still warns me every time I start and shut off the engine. What else in the system could make it think coolant is low? The reservoir is filled correctly but over time I do lose coolant. Not enough for a puddle on the ground but very gradually.

Also, my MPG is way down, probably 6 miles. I just put in a new K&N and that helped a little bit but still. I used to get 29 or so highway and 25ish city but now it's about 19 city. I don't drive like an idiot either, flooring it to every stoplight. I've heard O2 sensors can affect it or vacuums could but I don't know where to start with that. Any help for a novice car mechanic would be hugely appreciated. Thanks.

The car is a 1995 525i, m50 engine

[Russell]

Coolant sensor light may be due to bad wiring. Had the same issue and my indy repaired the wiring after I cleaned it a couple times. Believe it was the connector from the wiring harness.

MPG can be due to so many things. Air leak, tuneup, poor gas, weather. Also, I just cannot see how a K&N can help anything. Just my opinion.

[russiankid]

Try cleaning the connector. Mine was dirty and after cleaning it the problem went away.