BMW Repair: Fuel consumption & FM radio, rear windshield, poor mileage

Question
Tino,

You had advised me these issues before. This is an update & more questions after doing what you had advised.

I have a 1996 528i (136000 km) which gives very poor mileage (16
lt/100km in city) & (10 lt/100km on highway) . I have recently put in new spark plugs, changed air filter
& engine oil (5w 40) & got the fuel system cleaned (what they call
carbon cleaning). You had earlier advised me to try air pressure 32
(front) & 35 (rear) & premium fuel. The idling RPM is approx 650-750. No
errors shown in the computer check. The mileage for city driving is way
below what the technical manual specifies (11.8 lt/ 100km for city
driving. Any suggestions how it can be improved OR what might be wrong? I got
the compression checked, it comes up fine. The car still gives low mileage. Any idea what might be other problem areas to look for?

My FM radio had stopped working, you had suggested it might be due to
after market tinting which I had got removed from the rear wind shield.
The rear wind shield coil is working fine (defroster works). When I
clean the rear wind shield from inside with a glass cleaner, the FM radio
comes on & sometimes it stays on for a few days & other times for few
hours. But comes on whenever I clean the rear windshield. Any idea whats
happening here & how it can be fixed?

Thanks,

JM.


Answer
Hello Janak,
I am intrigued by your highway driving mileage. This is not a bad figure for a six cylinder car or even an old four cylinder car. 2.5 gallons (10 liters) reaching 100 kilometers equals
40 km./gallon divided by 1.6 equals 25 mpg. What more can you ask?
Your city driving may simply be on routes that are heavy in traffic and stops which result in frequent downshifts and braking. Naturally, this would be low.
Regarding your FM radio, even if you removed the tinting,
the damage had already been done. The damage I am referring to is the possible cutting of the wires of the ribbon antenna in your rear windshield. Proof is your statement that when you clean the area with glass cleaner (which has ammonia and most probably a little acid, contact is established). There is no BMW recommended cure for this situation.
Tino