Re: Audi 4.2 V8 big fuel consumption, other questions.

bad coolant sensor on back of right cylinder head will cause bad gas mileage. Use uses this sensor to enrich fuel during cold start up. If the ecu thinks the car is still cold due to faulty sensor, is will continue to enrich fuel even while warm. This is what cause poor mileage. I always change this sensor when I do the o2 sensor. Allan